AWS C5.5-2003 RP for Gas Tungsten Arc Welding

AWS C5.5/C5.5M:2003
An American National Standard
Recommended
Practices for
Gas Tungsten
Arc Welding
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
An American National Standard
Key Words —Gas tungsten arc welding, GTAW,
TIG, training, process, qualification,
equipment, quality, safe practices,
WIG, Heliarc®
Approved by
American National Standards Institute
June 4, 2003
Recommended Practices for
Gas Tungsten Arc Welding
Supersedes AWS C5.5-80
Prepared by
AWS C5 Committee on Arc Welding and Arc Cutting
Under the Direction of
AWS Technical Activities Committee
Approved by
AWS Board of Directors
Abstract
This document is designed to assist anyone who is associated with gas tungsten arc welding (GTAW). This includes
welders, welding technicians, welding engineers, quality control personnel, welding supervisors, purchasing personnel,
educators, and students.
This document discusses welding principles, equipment, gas shielding, and techniques for manual and automatic
GTAW. Welding safety, troubleshooting, and related items are included for understanding by all types of personnel in
establishing better production welding operations.
Educators will find this publication a handy reference for teaching all aspects of gas tungsten arc welding. It can
become a quick reference for students after their graduation or during their employment.
550 N.W. LeJeune Road, Miami, Florida 33126
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Statement on Use of AWS American National Standards
All standards (codes, specifications, recommended practices, methods, classifications, and guides) of the American
Welding Society (AWS) are voluntary consensus standards that have been developed in accordance with the rules of the
American National Standards Institute (ANSI). When AWS standards are either incorporated in, or made part of,
documents that are included in federal or state laws and regulations, or the regulations of other governmental bodies,
their provisions carry the full legal authority of the statute. In such cases, any changes in those AWS standards must be
approved by the governmental body having statutory jurisdiction before they can become a part of those laws and
regulations. In all cases, these standards carry the full legal authority of the contract or other document that invokes the
AWS standards. Where this contractual relationship exists, changes in or deviations from requirements of an AWS
standard must be by agreement between the contracting parties.
International Standard Book Number: 0-87171-715-8
American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126
© 2003 by American Welding Society. All rights reserved
Printed in the United States of America
AWS American National Standards are developed through a consensus standards development process that brings
together volunteers representing varied viewpoints and interests to achieve consensus. While AWS administers the process
and establishes rules to promote fairness in the development of consensus, it does not independently test, evaluate, or
verify the accuracy of any information or the soundness of any judgments contained in its standards.
AWS disclaims liability for any injury to persons or to property, or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this
standard. AWS also makes no guaranty or warranty as to the accuracy or completeness of any information published herein.
In issuing and making this standard available, AWS is not undertaking to render professional or other services for or on
behalf of any person or entity. Nor is AWS undertaking to perform any duty owed by any person or entity to someone
else. Anyone using these documents should rely on his or her own independent judgment or, as appropriate, seek the advice
of a competent professional in determining the exercise of reasonable care in any given circumstances.
This standard may be superseded by the issuance of new editions. Users should ensure that they have the latest edition.
Publication of this standard does not authorize infringement of any patent. AWS disclaims liability for the infringement
of any patent resulting from the use or reliance on this standard.
Finally, AWS does not monitor, police, or enforce compliance with this standard, nor does it have the power to do so.
On occasion, text, tables, or figures are printed incorrectly, constituting errata. Such errata, when discovered, are posted
on the AWS web page (www.aws.org).
Official interpretations of any of the technical requirements of this standard may be obtained by sending a request, in writing,
to the Managing Director, Technical Services Division, American Welding Society, 550 N.W. LeJeune Road, Miami, FL
33126 (see Annex A). With regard to technical inquiries made concerning AWS standards, oral opinions on AWS standards
may be rendered. However, such opinions represent only the personal opinions of the particular individuals giving them.
These individuals do not speak on behalf of AWS, nor do these oral opinions constitute official or unofficial opinions or interpretations of AWS. In addition, oral opinions are informal and should not be used as a substitute for an official interpretation.
This standard is subject to revision at any time by the AWS C5 Committee on Arc Welding and Arc Cutting. It must be
reviewed every five years, and if not revised, it must be either reapproved or withdrawn. Comments (recommendations,
additions, or deletions) and any pertinent data that may be of use in improving this standard are required and should be
addressed to AWS Headquarters. Such comments will receive careful consideration by the AWS C5 Committee on Arc
Welding and Arc Cutting and the author of the comments will be informed of the Committee’s response to the comments. Guests are invited to attend all meetings of the AWS C5 Committee on Arc Welding and Arc Cutting to express
their comments verbally. Procedures for appeal of an adverse decision concerning all such comments are provided in the
Rules of Operation of the Technical Activities Committee. A copy of these Rules can be obtained from the American
Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.
Photocopy Rights
Authorization to photocopy items for internal, personal, or educational classroom use only, or the internal, personal, or
educational classroom use only of specific clients, is granted by the American Welding Society (AWS) provided that the
appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, Tel: 978-750-8400;
online: http://www.copyright.com.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Personnel
AWS C5 Committee on Arc Welding and Arc Cutting
J. R. Hannahs, Chair
N. A. Sanders, 1st Vice Chair
D. B. Holliday, 2nd Vice Chair
P. Howe, Secretary
*E. R. Bohnart
H. A. Chambers
C. Connelly
J. DeVito
R. M. Dull
D. A. Fink
I. D. Harris
*R. T. Hemzacek
G. K. Hicken
K. Y. Lee
R. P. Munz
S. R. Potter
*B. L. Shultz
R. L. Strohl
*E. G. Yevick
L. Yost
Edison Community College
Hypertherm, Incorporated
Northrop Grumman Corporation
American Welding Society
Welding Education and Consulting
TRW Nelson Stud Welding Division
Poly-Weld, Incorporated
ESAB Welding and Cutting Products
Edison Welding Institute
The Lincoln Electric Company
Edison Welding Institute
Consultant
Sandia National Laboratory, Retired
The Lincoln Electric Company
The Lincoln Electric Company
SRP Consulting Services
The Taylor-Winfield Corporation
Tweco-Arcair Corporation
Weld-Met International Group
The Lincoln Electric Company
AWS C5C Subcommittee on Gas Tungsten Arc Welding
G. K. Hicken, Chair
R. D. Campbell, Vice Chair
P. Howe, Secretary
E. A. Benway
*E. R. Bohnart
*C. Connelly
D. E. Destefan
R. W. Diesner
J. C. Downey
T. W. Edwards
*J. R. Hannahs
*L. M. Hellemann
E. J. LaCoursiere
P. C. McClay
D. E. Spragg
*J. S. Thrower
D. A. Wright
*B. Young
Sandia National Laboratories, Retired
Purity Systems, Incorporated
American Welding Society
Swagelok Company
Welding and Education Consulting
Poly-Weld, Incorporated
High Current Technologies, Incorporated
Retired
Retired
American Welding and Engineering, Incorporated
Edison Community College
General Electric Aircraft Engines
EJL & Associates
Pratt and Whitney
Pratt and Whitney
Optimum Engineering Manufacturing, Incorporated
Zephyr Products, Incorporated
Westinghouse Savannah River Company, Retired
*Advisor
iii
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
This page is intentionally blank.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Foreword
(This Foreword is not a part of AWS C5.5/C5.5M:2003, Recommended Practices for
Gas Tungsten Arc Welding, but is included for informational purposes only.)
Gas tungsten arc welding (GTAW) was introduced as a practical fabricating process in the 1940s. In the decades since
then, advances have been made in the equipment and in the development of techniques for automatic applications.
GTAW is now accepted as the only practical joining method in some metal joining applications.
These recommended practices were first prepared by the AWS C5 Committee on Arc Welding and Arc Cutting and
the AWS C5C Subcommittee on Gas Tungsten Arc Welding in 1980. The 1980 edition was reaffirmed in 1989. The
current AWS C5 Committee on Arc Welding and Arc Cutting and the current C5C Subcommittee on GTAW have
prepared these recommended practices to present the basic practices and methods of GTAW and to expand the
document to include the latest advancements in this process. These recommended practices are based on present uses of
GTAW in the metal fabricating industry, along with research and development and new applications of the process.
We should all encourage our younger generation to consider welding and welding related fields as places to become
involved with the high rewards and challenges to be encountered in the future. We should also be willing and pleased to
share our prior experiences and knowledge that could help new members excel in this occupation.
The description of GTAW and its features are presented here as clearly and concisely as possible. The Committee has
developed these guidelines in the hope that they would lead to further development of the GTAW process and, thus, to
higher quality and performance standards.
Comments and suggestions for the improvement of this standard are welcomed. They should be sent to the Secretary,
AWS C5 Committee on Arc Welding and Arc Cutting, American Welding Society, 550 N.W. LeJeune Road, Miami, FL
33126.
Official interpretations of any of the technical requirements of this standard may be obtained by sending a request,
in writing, to the Managing Director, Technical Services Division, American Welding Society. A formal reply will be
issued after it has been reviewed by the appropriate personnel following established procedures. Guidelines for technical
inquiries regarding AWS standards are shown in Annex A.
This document will be reviewed periodically to assure its success in serving all parties concerned with its provisions.
Revisions will be issued when warranted.
v
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
This page is intentionally blank.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Table of Contents
Page No.
Personnel .................................................................................................................................................................... iii
Foreword.......................................................................................................................................................................v
List of Tables.................................................................................................................................................................x
List of Figures..............................................................................................................................................................xi
1. Scope and Introduction ........................................................................................................................................1
1.1 Scope .........................................................................................................................................................1
1.2 Introduction to the Gas Tungsten Arc Welding (GTAW) Process.............................................................1
1.3 History.......................................................................................................................................................1
2. Normative References ..........................................................................................................................................4
2.1 American Conference of Governmental Industrial Hygienists Standards ................................................5
2.2 AWS Standards..........................................................................................................................................5
2.3 ISO Standards............................................................................................................................................6
2.4 OSHA Standards .......................................................................................................................................6
3. Definitions .............................................................................................................................................................6
4. GTAW Principles .................................................................................................................................................9
4.1 Process Description ...................................................................................................................................9
4.2 Process Advantages...................................................................................................................................9
4.3 Process Limitations .................................................................................................................................11
4.4 Process Variables.....................................................................................................................................12
4.5 Related Variables.....................................................................................................................................17
5. Equipment and Supplies.....................................................................................................................................18
5.1 Welding Power Sources (Used for GTAW)—Introduction .....................................................................18
5.2 Controllers...............................................................................................................................................20
5.3 Pulse Controllers .....................................................................................................................................22
5.4 Weld Sequence Controllers .....................................................................................................................22
5.5 Arc Welding Torches...............................................................................................................................23
5.6 Wire Feeders............................................................................................................................................30
5.7 Arc and Torch Oscillators........................................................................................................................31
5.8 Arc Initiation Equipment.........................................................................................................................32
6. Tungsten Electrodes ...........................................................................................................................................33
6.1 General ....................................................................................................................................................33
6.2 Classifications of Electrodes ...................................................................................................................34
6.3 Surface Finishes ......................................................................................................................................37
6.4 Electrode Sizes and Current Capacities ..................................................................................................37
6.5 Electrode Tip Configurations ..................................................................................................................38
6.6 Electrode Cutting.....................................................................................................................................41
6.7 Factors Affecting Electrode Life .............................................................................................................41
6.8 Removing Contamination .......................................................................................................................42
6.9 Grinding Dust..........................................................................................................................................42
6.10 Storage.....................................................................................................................................................43
7. Gas Shielding, Purging, and Backing ................................................................................................................43
7.1 Torch Shielding Gas ................................................................................................................................43
vii
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Page No.
7.2
7.3
7.4
7.5
7.6
Purging ....................................................................................................................................................50
Shielding and Purging Gas Purity ...........................................................................................................62
Shielding and Purging Gas Economics ...................................................................................................65
Purifiers ...................................................................................................................................................65
Purging Gas Safety..................................................................................................................................67
8. Fixturing and Tooling.........................................................................................................................................68
8.1 Material Selection ...................................................................................................................................68
8.2 Tooling/Fixturing Considerations............................................................................................................68
8.3 Temporary (Soft)/Permanent (Hard) Tooling..........................................................................................69
9. Welding Techniques ...........................................................................................................................................71
9.1 General ....................................................................................................................................................71
9.2 Manual and Semiautomatic Welding ......................................................................................................71
9.3 Mechanized Welding...............................................................................................................................80
9.4 Automated Welding.................................................................................................................................83
10. Joint Design, Preparation, and Welding Positions .............................................................................................85
10.1 Introduction .............................................................................................................................................85
10.2 Basic Joint Configurations and Welding Positions .................................................................................85
10.3 Edge Preparation and Surface Cleaning..................................................................................................85
11. Welding Characteristics of Selected Alloys .......................................................................................................85
11.1 Introduction .............................................................................................................................................85
11.2 Carbon and Alloy Steels..........................................................................................................................89
11.3 Stainless Steels and Iron-Based Superalloys...........................................................................................89
11.4 Aluminum Alloys ....................................................................................................................................90
11.5 Magnesium Alloys ..................................................................................................................................91
11.6 Beryllium.................................................................................................................................................91
11.7 Copper Alloys .........................................................................................................................................91
11.8 Nickel Alloys...........................................................................................................................................92
11.9 Cobalt Alloys...........................................................................................................................................92
11.10 Refractory and Reactive Metals ..............................................................................................................92
11.11 Cast Irons.................................................................................................................................................92
11.12 Welding Dissimilar Materials..................................................................................................................92
11.13 Filler Metals ............................................................................................................................................92
12. Qualification of Procedures, Welders, and Welding Operators..........................................................................94
12.1 Introduction .............................................................................................................................................94
12.2 Welding Program.....................................................................................................................................95
12.3 Establishing Welding Requirements .......................................................................................................95
12.4 Welding Procedure Specifications (WPS)...............................................................................................95
12.5 Procedure Qualification Records (PQR) .................................................................................................95
12.6 Welder and Welding Operator Qualification Tests..................................................................................95
13. Quality Control ..................................................................................................................................................96
13.1 Introduction .............................................................................................................................................96
13.2 Weldment Quality....................................................................................................................................96
13.3 Specifications ..........................................................................................................................................96
14. Troubleshooting .................................................................................................................................................97
14.1 General ....................................................................................................................................................97
14.2 Electrical..................................................................................................................................................97
14.3 Inert Shielding Gas Troubleshooting ....................................................................................................102
14.4 Water Cooling Systems .........................................................................................................................105
14.5 Tools and Fixtures .................................................................................................................................106
viii
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Page No.
14.6 Filler Material........................................................................................................................................106
14.7 Design of Welded Assemblies...............................................................................................................106
14.8 Weld Joint Fit-up ...................................................................................................................................108
15. Safety ...............................................................................................................................................................108
15.1 Hazards..................................................................................................................................................108
15.2 Electrical Shock.....................................................................................................................................108
15.3 Arc Radiation and Burns .......................................................................................................................108
15.4 Welding Environment............................................................................................................................109
15.5 Oxygen Deficiency................................................................................................................................110
15.6 Noise......................................................................................................................................................110
15.7 Safe Handling of Cylinders ...................................................................................................................110
15.8 Fires And Explosions ............................................................................................................................110
15.9 Common Sense......................................................................................................................................110
15.10 Grinding Dust........................................................................................................................................110
Nonmandatory Annexes............................................................................................................................................113
Annex A—Guidelines for Preparation of Technical Inquiries for AWS Technical Committees................................113
Annex B—Suggested Reading List and Other References ........................................................................................115
List of AWS Documents on Arc Welding and Arc Cutting ........................................................................................117
ix
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
List of Tables
Table
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Page No.
Welding Process Comparison Based on Quality and Economics ................................................................11
Comparison of Typical Current Ratings for Gas-Cooled and Water-Cooled GTAW Torches.....................25
Typical Welding Cable Capacities ...............................................................................................................29
Guide for Selecting the Size of Cable Based on the Welding Current.........................................................30
Chemical Composition Requirements for Tungsten Electrodes ..................................................................34
Typical Current Ranges for Tungsten Electrodes and Recommended Gas Cup Sizes ................................35
Comparison of Surface Finish Designations................................................................................................37
Recommended Types of Current, Tungsten Electrodes, and Shielding Gases for Welding of
Various Metals and Alloys ...........................................................................................................................39
Tungsten Electrode Tip Shapes and Examples of Current Ranges ..............................................................39
General Properties of Gases .........................................................................................................................44
Thermodynamic Properties of Gases ...........................................................................................................44
Dew Point Conversions ................................................................................................................................45
Advantages of Shielding Gases....................................................................................................................46
Typical Argon Flow Rates............................................................................................................................50
Gas Purity Specification by Industrial Grade...............................................................................................62
Purity Requirements for Gaseous Argon .....................................................................................................62
Purity Requirements for Gaseous Helium ...................................................................................................63
Purity Requirements for Gaseous Hydrogen ...............................................................................................63
Welding Equipment or Components ............................................................................................................72
AWS Specifications Related to Gas Tungsten Arc Welding........................................................................88
Troubleshooting ...........................................................................................................................................98
Guide for Shade Numbers..........................................................................................................................109
x
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
List of Figures
Figure
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Page No.
Early Gas Tungsten Arc Welding Torches and Accessories, Circa 1943, with a Torch Body
and an Early Flowmeter .................................................................................................................................2
Early Gas Tungsten Arc Welding Torches .....................................................................................................2
SMAW Power Source Used for Early Gas Tungsten Arc Welding ...............................................................3
Motor-Generator SMAW Power Source Used for Early Gas Tungsten Arc Welding ...................................3
Gas Tungsten Arc Welding Power Source—Pulsed ......................................................................................4
Gas Tungsten Arc Welding Power Source .....................................................................................................4
Stylized Representation of the Gas Tungsten Arc Welding Process..............................................................9
Gas-Cooled GTAW Torch and Stylized Representation of Typical Gas Tungsten Arc Welding
Equipment ....................................................................................................................................................10
Clean Weld Beads Typical of Properly Shielded GTAW Welds ..................................................................11
Characteristics of Current Types Used for Gas Tungsten Arc Welding.......................................................13
Relationship Between Arc Pressure and Pulse Frequency...........................................................................14
Programmed (Modulated) Current without Polarity Reversal .....................................................................15
Characteristics of Variable Polarity (Programmed) Weld Current...............................................................16
Arc Shape and Fusion Zone Profiles as a Function of Electrode Tip Geometry in Pure Argon
Shielding Gas ...............................................................................................................................................17
Typical Volt-Amp Characteristic Curves for GTAW Power Sources...........................................................18
Typical Inverter Power Source Components................................................................................................20
Typical Wire Feeder .....................................................................................................................................22
Typical GTAW Sequence for Non-Pulsed DC Welding...............................................................................23
Typical GTAW Sequence for Pulsed DC Current and Pulsed Wire Feed ....................................................24
Typical Water-Cooled GTAW Torch (Cross-Sectional View)......................................................................25
Examples of GTAW Torches........................................................................................................................26
Orbital Weld Head with Wire Feeder...........................................................................................................27
Components of a Typical GTAW Torch, Including Gas Nozzle/Cup, Gas Lens, Collet Body,
Torch Body, Collet, and Electrode ...............................................................................................................27
GTAW Torch Without a Gas Lens (Left) and with a Gas Lens (Right) .......................................................28
GTAW Torch with Cold Wire Feed..............................................................................................................31
Schematic of GTAW with Hot Wire Feed....................................................................................................31
Magnetically Deflected Arc Laying a Stringer Bead in a Deep Groove Weld ............................................32
Cross Sections of Welds Made in 1/2 in. [13 mm] Thick Stainless Steel; (A) with Magnetic Arc
Oscillation, and (B) without Magnetic Arc Oscillation ...............................................................................32
High-Frequency Arc Starting.......................................................................................................................33
Balled Tip on the End of a Pure Tungsten Electrode Used for AC Welding ...............................................36
Ground Tapered Tip on End of Doped Tungsten Electrodes .......................................................................38
Ground Electrode Tip Geometry..................................................................................................................39
Typical Preparation Method of Tungsten Electrodes Used for GTA Welding, Including
Tip Truncation, Grinding, and Cutting.........................................................................................................40
The Desired Surface Finish of a Ground Electrode .....................................................................................41
Proper Cutting of Tungsten Electrodes with a Diamond Cut-Off Blade .....................................................42
GTA Weld Bead Shape as a Function of Shielding Gas Composition and Electrode
Tip Geometry (on 304 Stainless Steel) ........................................................................................................47
GTA Voltage—Current Relationships with Argon and Helium Shielding Gases for
Different Arc Lengths ..................................................................................................................................48
xi
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Figure
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
Page No.
Monel®1
Improved Surface Cleanliness on
Welds Produced with the 5% Hydrogen Mixture
in Argon Shielding Gas with GTAW ...........................................................................................................49
The Effects of Shielding Gas Contamination on Titanium Weldments (Color Chart for
Titanium Welding Acceptance)....................................................................................................................51
GTAW Weld Underbead Contamination with Various Levels of Oxygen Contents in the Purging Gas.........52
Purging Times for Various Pipe Sizes..........................................................................................................54
Purging a Piping System with Open Ends Blanked .....................................................................................55
Purging of a Piping System with Appropriate Venting to Eliminate Dead Air Pockets ..............................55
Purging with Removable Plugs ....................................................................................................................56
Purging with Removable Chamber ..............................................................................................................56
Purge Distributor Ring .................................................................................................................................56
Purging with Water Soluble Paper Dams .....................................................................................................57
Purging with a Backing Channel..................................................................................................................57
Purging with a Gas Distributor (Diffuser)....................................................................................................58
Typical Inert Gas Glove Box Chamber ........................................................................................................58
Flexible Plastic Purge Bag ...........................................................................................................................59
Trailing Shields—Bottom View of Inert Gas Trailing Shield Fabricated Using Stainless Porous
(100 micron) Tubing (Shown with High Temperature Tape)......................................................................60
Trailing Shields—Inert Gas Trailing Shield Fabricated Using Stainless Porous (100 micron) Tubing
(Shown with High Temperature Tape) .........................................................................................................60
Trailing Shields—Inert Gas Trailing Shield Fabricated Using Stainless Porous (40–100 micron)
Sheet Metal ..................................................................................................................................................61
Shielding with the Use of a Backing Tape ...................................................................................................61
Point-of-Use (POU) Purifiers (Waferpure®2 Reactive Resin Type) Below a Welding Fixture....................66
Point-of-Use Gas Purifier (Heated Metal Getter Type) ...............................................................................67
Cylinder Status Tag (The Use of a Simple Tagging System Can Be Very Helpful) ....................................68
Weld Distortion in Ti-6Al-V Bead-on-Plate (Sheet) Weld ..........................................................................69
Tooling for GTAW of Fuel Cell Components to Control Distortion of Weldment......................................70
Run-On/Run-Off Tabs Used for Welding Ends of Strip Material................................................................70
Walking-the-Cup Technique ........................................................................................................................74
Dragging-the-Finger Technique ...................................................................................................................74
Folding Fingerstall Technique......................................................................................................................75
Brace Technique Showing Wrist in Contact with Workpiece to Stabilize the Torch...................................75
Small Rotary Positioner Used for Workpiece Manipulation........................................................................76
Mechanical Manipulation in a Mechanized Welder.....................................................................................76
Gas Tungsten Arc Welding Torch with Wire Feeders [(A) and (B)] for Spooled Wire...............................78
Cross Sections of Typical Consumable Inserts ............................................................................................79
Lathe-Type Welding Setup...........................................................................................................................81
Orbital GTAW Weld Head ...........................................................................................................................84
Basic Joint Types..........................................................................................................................................86
Weld Joint Edge Preparation (U-Groove, J-Groove, and V-Groove) ...........................................................87
Effects of Sulfur Content on Bead-on-Plate Weld Bead Shape in 304L Made with the
Same Parameters ..........................................................................................................................................90
GTAW in 6061-0 Aluminum Showing the Surface Contours with Pulsed Direct Current
Straight Polarity (DCEN).............................................................................................................................91
High Quality Welds in Inconel®1 718, Original Scale 5X ...........................................................................93
High Quality Welds in Cobalt Alloy HS188, Original Scale 5X .................................................................93
Manual GTAW of Titanium in an Inert Gas Chamber (Glove Box) ............................................................94
Criteria for Acceptable GTAW in Titanium via Tack Welds Only ............................................................104
1. Monel and Inconel are registered trademarks of Special Metals Corporation.
2. Waferpure is a registered trademark of Mykrolis Corporation.
xii
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Recommended Practices for
Gas Tungsten Arc Welding
1. Scope and Introduction
ples of this would be certain welded metal sculptures
and/or a “perfectly” welded part or assembly. The
“science” end of the spectrum would include recent
developments such as fully automated robotic welding
cells that could include through-the-torch vision that
allows real-time viewing of the weld as well as real-time
weld joint tracking. Also, weld parameter data acquisition and feedback control are routinely accomplished in
real-time.
1.1 Scope. This document presents recommended practices for the gas tungsten arc welding (GTAW) process.1
Its purpose is to provide a fundamental explanation of
the process, describe basic practices and concepts, and
outline some advanced methods and applications of
GTAW. These should enable welding personnel to determine the best applications of this process and evaluate its
use compared with other joining processes.
The section covering principles of operation will help
the reader understand how the process works, the general
types of equipment needed, and the advantages and limitations of the gas tungsten arc welding process. The basic
concepts and practices include both general and specific
recommendations and technical data for equipment, consumables, procedures, variables, applications, and safety
considerations.
This standard makes use of U.S. Customary Units.
Approximate mathematical equivalents in the International System of Units (SI) are provided for comparison in brackets [ ] or in appropriate columns in tables and
figures.
1.3 History. Although arc welding was first developed in
the 1880s, its commercial use in the United States did not
commence until the first decade of the 1900s. The years
of the First World War brought the initial large-scale
commercial use of arc welding, when shielded metal arc
welding (SMAW) began to replace riveting as the means
of joining in the manufacture of ships.
During the 1920s, H. M. Hobart and P. K. Devers performed preliminary work on using inert gases to shield
the carbon or metallic electrode’s welding arc and molten
weld pool. In 1926 they applied for patents2 on the use of
an electric welding arc in which an inert gas was independently supplied around the arc, thus replacing flux as
the shielding method. Other investigators experimented
with both helium and argon as shielding gases, but because of the high costs associated with these inert gases,
very little commercial use was made of them at that time.
1.2 Introduction to the Gas Tungsten Arc Welding
(GTAW) Process. Welding as an occupation and a career is a very “special” and rewarding choice to pursue. It
is one of the most interesting manufacturing disciplines
as it involves both art and science. This is illustrated by
manual gas tungsten arc welding (GTAW) because a person’s manual dexterity, hand-eye coordination, and selfdiscipline in combination with the correct welding procedure(s) are paramount to its success. The “art” portion is
most evident when an individual welder expresses their
unique signature to the manually applied welds. Exam-
By the onset of the Second World War, shielded metal
arc welding had become the dominant welding process.
However, there was a need within the aircraft industry
for welds made with better shielding than that provided
by SMAW when joining reactive metals such as aluminum and magnesium. Also, in the aircraft industry there
was a need to develop an acceptable welding process to
replace riveting for joining of thin gage materials. These
needs led to the first commercial development of gas
tungsten arc welding equipment.
1. Gas tungsten arc welding is defined as an arc welding process that uses an arc between a tungsten electrode (nonconsumable) and the weld pool. The process is used with shielding
gas and without the application of pressure. (Ref. AWS A3.0,
Standard Welding Terms and Definitions.)
2. H. M. Hobart, U.S. Patent 1,746,081, 2/4/1930 and P. K.
Devers, U.S. Patent 1,746,191, 2/4/1930.
1
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Figure 1—Early Gas Tungsten Arc Welding Torches and Accessories,
Circa 1943, with a Torch Body and an Early Flowmeter
In 1941, R. Meredith and V. H. Pavlecka developed
the first practical electrode holders (torches) using a
nonconsumable electrode made from tungsten. These
first torches were simply shielded metal arc welding
electrode holders that had been modified to provide the
shielding gas flow. A 1/8 in. [3 mm] diameter tungsten
electrode was held in a copper tube through which the
inert helium gas flowed to protect the electrode, weld
pool, and adjacent heated areas of the workpiece. Helium
was elected to provide the necessary shield because,
at the time, it was the only readily available inert gas.
Tungsten inert gas torches and accessories typical of that
period are shown in Figures 1 and 2.3 A patent was
issued for this process in 1942.4
This arc welding process was initially named
“Heliarc®,” 5, 6 welding because helium was used as the
shielding gas. It has also been called nonconsumable
electrode welding, tungsten inert gas (TIG) welding,
wolfram inert gas (WIG) welding7 and tungsten-arc
welding. However, the proper AWS terminology for this
process is gas tungsten arc welding (GTAW), because
shielding gas mixtures containing inert gases other than
helium, or gases which are not inert, are sometimes used.
Using a tungsten electrode and direct current power
source, a stable, efficient heat source (the arc) was used
to produce acceptable welds. The inert shielding gas provided full protection of the arc and weld pool, which was
imperative in welding of aluminum and magnesium, because even a small amount of air could contaminate the
weld. The process also allows for better control over the
heat input, thus making it easier to weld thin materials.
3. Reprinted with permission from “Modern Welding Technology,” H. B. Cary, 2nd Edition, Prentice Hall, NJ 1989, Figure 1-9,
p. 8.
4. R. Meredith, U.S. Patent 2,274,631. 2/24/1942.
5. Registered trademark of ESAB.
6. “Heliweld” was the Airco description of the process.
7. Wolfram is the German name for tungsten.
Figure 2—Early Gas Tungsten
Arc Welding Torches
2
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Figure 4—Motor-Generator SMAW
Power Source Used for Early
Gas Tungsten Arc Welding
ever, because it did not provide the cleaning action like
DCEP, it was not acceptable for welding of aluminum
or magnesium, which have tenacious surface oxides
that must be removed before acceptable welds can be
produced.
To obtain the cleaning action of DCEP along with the
improved penetration characteristics and lower electrode
heating of DCEN, alternating current (AC) welding
power sources were developed. A high-frequency, highvoltage current was superimposed over the basic welding
current to stabilize the arc during current reversals. This
method was successfully applied to GTAW of aluminum
and magnesium.
By the early 1950s, GTAW had gained acceptance in
the welding industry. Argon was the most widely accepted shielding gas, followed by helium. However, because of the high cost of argon and helium gases, carbon
dioxide and nitrogen were investigated as shielding
gases. Since that time, numerous other gases and mixtures of gases have been used with this welding process
to provide improved welding performance for some
metals. These include argon-helium mixtures, argonhydrogen mixtures, and argon-nitrogen mixtures.
As a tool for increasing deposition rates beyond that
of the commonly used cold wire feed during gas tungsten
arc welding, the hot wire feed method8 of filler metal
addition was introduced. This allowed the high quality
Figure 3—SMAW Power Source Used for
Early Gas Tungsten Arc Welding
When the GTAW process was first developed, SMAW
was being performed utilizing direct current with electrode positive (DCEP or reverse polarity). The same
power sources (DC generators of the rotating type) were
thus used for the early gas tungsten arc welding process.
Photographs of early GTAW/SMAW power sources are
shown in Figures 3 and 4. One of the major benefits of
DCEP was the tremendous cathodic cleaning action of
the workpiece surface for aluminum and magnesium.
However, overheating of the electrode and subsequent
splitting, melting, and transfer of tungsten particles into
the weld limited the useful current range. Since these
early torches were air-cooled, they had only a 75 A current capacity. As a result, it soon became apparent that
DCEP was not the best polarity to use for this process.
By making the electrode negative, overheating was
avoided and weld penetration was improved. Use of
DC electrode negative (DCEN or straight polarity)
proved acceptable for welding of stainless steels. How-
8. A. F. Manz, U.S. Patent 3,122,629, File 2562, issued 2/25/1964.
3
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Figure 5—Gas Tungsten Arc Welding
Power Source —Pulsed
Figure 6—Gas Tungsten Arc Welding
Power Source
welds produced by the GTAW process without incurring
the spatter produced by the consumable electrode
processes.
compositions have been developed for improved arc
starting, arc stability, and electrode life. GTAW systems
are available with several tungsten electrodes positioned
around the part to be welded, or impinging on a single
weld pool.
Over the last several decades, numerous improvements have been made to the GTAW equipment, process
and controls. Welding power sources have been developed specifically for the GTAW process (see Figures 5
and 6). Some provide pulsed direct current and others
produce variable polarity alternating welding current.
Automatic arc starting systems, automatic arc length/
voltage controls, vision and penetration sensors, and
positioning equipment are all commercially available.
Computer controls, automatic sequence controls, and
data acquisition systems are readily available to allow
data recording and statistical process control. Watercooled torches were developed, which allow welding
currents of up to 1500 A. Different tungsten electrode
2. Normative References
If a code or other standard is cited without a date of
publication, it is understood that the latest edition of the
document referred to applies. As codes and other standards undergo frequent revision, the reader is encouraged
to consult the most recent edition. If a code or other standard is cited with the date of publication, the citation refers to that edition only, and it is understood that any
future revisions or amendments to the code or standard
are not included.
4
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
2.1 American Conference of Governmental Industrial
Hygienists Standards9
(1) ACGIH, Threshold Limit Values for Chemical
Substances and Physical Agents and Biological Exposure Indices
(20) AWS B2.1, Specification for Welding Procedure
and Performance Qualification
(21) AWS B2.1-1-002, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding of Carbon Steel, (M-1/P-1, Group 1 or 2), 3/16 through 7/8 inch,
in the As-Welded Condition, With or Without Backing
(22) AWS B2.1-1-007, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of
Galvanized Steel (M-1), 18 through 10 Gauge, in the AsWelded Condition, with or without Backing
(23) AWS B2.1-1-008, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of
Carbon Steel (M-1, P-1, or S-1), 18 through 10 Gauge,
in the As-Welded Condition, with or without Backing
(24) AWS B2.1-1-009, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of Austenitic Stainless Steel (M-8, P-8, or S-8), 18 through 10
Gauge, in the As-Welded Condition, with or without Backing
(25) AWS B2.1-1/8-010, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of
Carbon Steel to Austenitic Stainless Steel (M-1, P-1, or
S-1 to M-8, P-8, or S-8), 18 through 10 Gauge, in the AsWelded Condition, with or without Backing
(26) AWS B2.1-22-015, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of
Aluminum (M/P/S-22 to M/P/S-22), 18 through 10 Gauge,
in the As-Welded Condition, with or without Backing
(27) AWS B2.1-1-021, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding Followed by Shielded Metal Arc Welding of Carbon Steel
(M-1/P-1/S-1, Group 1 or 2), 1/8 through 1-1/2 inch
Thick, ER70S-2 and E7018, As-Welded or PWHT Condition (primarily for pipe applications)
(28) AWS B2.1-8-024, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding
Followed by Shielded Metal Arc Welding of Austenitic Stainless Steel (M-8/P-8/S-8, Group 1), 1/8 through
1-1/2 inch Thick, ER3XX and E3XX-XX, As-Welded Condition, Primarily Plate and Structural Applications.
(29) AWS B2.1-8-025, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding of
Austenitic Stainless Steel (M-8/P-8/S-8, Group 1), 1/16
through 1-1/2 inch Thick, ER3XX, As-Welded Condition,
Primarily Plate and Structural Applications.
(30) ANSI/AWS B2.1-1-207, Standard Welding Procedure Specification (WPS) for Gas Tungsten Arc Welding of Carbon Steel (M-1/P-1/S-1, Group 1 or 2), 1/8
through 1-1/2 inch Thick, ER70S-2, As-Welded or PWHT
Condition, Primarily Pipe Applications
(31) ANSI/AWS B2.1-1-209, Standard Welding
Procedure Specification (WPS) for Gas Tungsten Arc
Welding Followed by Shielded Metal Arc Welding of
Carbon Steel (M-1/P-1/S-1, Group 1 or 2), 1/8 through
1-1/2 inch Thick, ER70S-2 and E7018, As-Welded or
PWHT Condition, Primarily Pipe Applications
2.2 AWS Standards10
(1) ANSI Z49.1, Safety in Welding, Cutting, and
Allied Processes
(2) AWS A1.1, Metric Practice Guide for the Welding Industry
(3) AWS A3.0, Standard Welding Terms and Definitions
(4) AWS A5.7, Specification for Copper and Copper
Alloy Bare Welding Rods and Electrodes
(5) AWS A5.9, Specification for Bare Stainless Steel
Welding Electrodes and Rods
(6) AWS A5.10/A5.10M, Specification for Bare Aluminum and Aluminum Alloy Welding Electrodes and Rods
(7) AWS A5.12/A5.12M, Specification for Tungsten
and Tungsten Alloy Electrodes for Arc Welding and
Cutting
(8) AWS A5.13, Specification for Surfacing Welding
Electrodes for Shielded Metal Arc Welding
(9) AWS A5.14/A5.14M, Specification for Nickel
and Nickel-Alloy Bare Welding Electrodes and Rods
(10) AWS A5.15, Specification for Welding Electrodes
and Rods for Cast Iron
(11) AWS A5.16, Specification for Titanium and Titanium Alloy Welding Electrodes and Rods
(12) AWS A5.18/A5.18M, Specification for Carbon
Steel Electrodes and Rods for Gas Shielded Arc Welding
(13) AWS A5.19, Specification for Magnesium-Alloy
Welding Electrodes and Rods
(14) AWS A5.21, Specification for Bare Electrodes
and Rods for Surfacing
(15) AWS A5.22, Specification for Stainless Steel
Electrodes for Flux Cored Arc Welding and Stainless
Steel Flux Cored Rods for Gas Tungsten Arc Welding
(16) AWS A5.24, Specification for Zirconium and Zirconium Alloy Welding Electrodes and Rods
(17) AWS A5.28, Specification for Low Alloy Steel
Electrodes and Rods for Gas Shielded Arc Welding
(18) AWS A5.30, Specification for Consumable Inserts
(19) AWS A5.32, Specification for Welding Shielding
Gases
9. Available through American Conference of Governmental
Industrial Hygienists, 1330 Kemper Meadow Drive, Cincinnati, OH 45240-1634.
10. Available through Global Engineering Documents, Handling
Services Group, 15 Inverness Way East, Englewood, CO
80112-5776, (800) 854-7179 (303) 397-7956, Fax (303) 3972740, Internet: www.global.ihs.com.
5
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
(32) AWS B2.1-1-210, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding with
Consumable Insert Root of Carbon Steel (M-1/P-1/S-1,
Group 1 or 2), 1/8 through 1-1/2 inch Thick, INMs-1 and
ER70S-2, As-Welded Condition, Primarily Pipe Applications
(33) AWS B2.1-1-211, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding with
Consumable Insert Root followed by Shielded Metal Arc
Welding of Carbon Steel (M-1/P-1/S-1, Group 1 or 2), 1/8
through 1-1/2 inch Thick, INMs-1, ER70S-2, and E7018, AsWelded or PWHT Condition, Primarily Pipe Applications
(34) AWS B2.1-8-212, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding of
Austenitic Stainless Steel (M-8/P-8/S-8, Group 1), 1/16
through 1-1/2 inch Thick, ER3XX, As-Welded Condition,
Primarily Pipe Applications
(35) AWS B2.1-8-214, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding
followed by Shielded Metal Arc Welding of Austenitic Stainless Steel (M-8/P-8/S-8, Group 1), 1/8 through
1-1/2 inch Thick, ER3XX and E3XX-XX, As-Welded Condition, Primarily Pipe Applications
(36) AWS B2.1-8-215, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding
with Consumable Inserts of Austenitic Stainless Steel
(M-8/P-8/S-8, Group 1), 1/8 through 1-1/2 inch Thick,
IN3XX and ER3XX, As-Welded Condition, Primarily
Pipe Applications
(37) AWS B2.1-8-216, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding with
Consumable Insert Followed by Shielded Metal Arc Welding of Austenitic Stainless Steel (M-8/P-8/S-8, Group 1),
1/8 through 1-1/2 inch Thick, IN3XX, ER3XX and ER3XXXX, As-Welded Condition, Primarily Pipe Applications
(38) AWS B2.1-4-217, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding of
Chromium-Molybdenum Steel (M-4/P-4, Group 1 or 2),
ER80S-B2, 1/8 through 1/2 inch Thick, As-Welded Condition, 1/8 through 1-1/2 inch Thick, PWHT Condition,
Primarily Pipe Applications
(39) AWS B2.1-4-219, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding
followed by Shielded Metal Arc Welding of ChromiumMolybdenum Steel (M-4/P-4, Group 1 or 2), 1/8 through
1/2 inch Thick, As-Welded Condition, 1/8 through
1-1/2 inch Thick, PWHT Condition, ER80S-B2 and
E8018-B2, Primarily Pipe Applications
(40) AWS B2.1-4-220, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding
(Consumable Insert Root) of Chromium-Molybdenum Steel
(M-4/P-4, Group 1 or 2), 1/8 through 1/2 inch Thick, AsWelded Condition, 1/8 through 3/4 inch Thick, PWHT Condition, IN515 and ER80S-B2, Primarily Pipe Applications
(41) AWS B2.1-4-221, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding (Consumable Insert Root) followed by Shielded Metal Arc Welding of Chromium-Molybdenum Steel (M-4/P-4, Group 1 or
2), 1/8 through 1/2 inch Thick, As-Welded Condition, 1/8
through 1-1/2 inch Thick, PWHT Condition, IN515 and
ER80S-B2, and E8018-B2, Primarily Pipe Applications
(42) AWS B2.1-5A-222, Standard Welding Procedure Specification (WPS) for Gas Tungsten Arc Welding
of Chromium-Molybdenum Steel (M-5A/P-5A), ER90S-B3,
1/8 through 1/2 inch Thick, As-Welded Condition, 1/8
through 3/4 inch Thick, PWHT Condition, Primarily
Pipe Applications
(43) AWS B2.1-5A-224, Standard Welding Procedure Specification (WPS) for Gas Tungsten Arc Welding
followed by Shielded Metal Arc Welding of ChromiumMolybdenum Steel (M-5A/P-5A), 1/8 through 1/2 inch
Thick, As-Welded Condition, 1/8 through 1-1/2 inch
Thick, PWHT Condition, ER90S-B3 and E9018-B3, Primarily Pipe Applications
(44) AWS B2.1-5A-225, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding (Consumable Insert Root) of Chromium-Molybdenum Steel
(M-5A/P-5A), 1/8 through 1/2 inch Thick, As-Welded
Condition, 1/8 through 3/4 inch Thick, PWHT Condition,
IN521 and ER90S-B3, Primarily Pipe Applications
(45) AWS B2.1-5A-226, Standard Welding Procedure
Specification (WPS) for Gas Tungsten Arc Welding (Consumable Insert Root) followed by Shielded Metal Arc
Welding of Chromium-Molybdenum Steel (M-5A/P-5A),
1/8 through 1/2 inch Thick, As-Welded Condition, 1/8
through 1-1/2 inch Thick, PWHT Condition, IN521 and
ER90S-B3, and E9018-B3, Primarily Pipe Applications
(46) AWS B2.1-1/8-227, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding of
Carbon Steel (M-1/P-1/S-1, Groups 1 or 2) to Austenitic
Stainless Steel (M-8/P-8/S-8, Group 1), 1/16 through
1-1/2 inch Thick, ER309(L), As-Welded Condition, Primarily Pipe Applications
(47) AWS B2.1-1/8-229, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding
followed by Shielded Metal Arc Welding of Carbon Steel
(M-1/P-1/S-1, Groups 1 or 2) to Austenitic Stainless
Steel (M-8/P-8/S-8, Group 1), 1/8 through 1-1/2 inch
Thick, ER309(L) And ER309(L)-15, -16, or -17, AsWelded Condition, Primarily Pipe Applications
(48) AWS B2.1-1/8-230, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding
with Consumable Insert Root of Carbon Steel (M-1/P-1/
S-1, Groups 1 or 2) to Austenitic Stainless Steel (M-8/P-8/
S-8, Group 1), 1/16 through 1-1/2 inch Thick, IN309
and ER309(L), As-Welded Condition, Primarily Pipe
Applications
6
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
(49) AWS B2.1-1/8-231, Standard Welding Procedure
Specification (SWPS) for Gas Tungsten Arc Welding with
Consumable Insert Root followed byShielded Metal Arc
Welding of Carbon Steel (M-1/P-1/S-1, Groups 1 or 2) to
Austenitic Stainless Steel (M-8/P-8/S-8, Group 1), 1/8
through 1-1/2 inch Thick, IN309 and ER309, and E309-15,
-16, or -17, or IN309, ER309(L), and ER309(L)-15, -16, or
-17, As-Welded Condition, Primarily Pipe Applications
(50) AWS C5.10, Recommended Practices for Shielding Gases for Welding and Plasma Arc Cutting
(51) AWS D1.1, Structural Welding Code—Steel
(52) AWS D1.2, Structural Welding Code—Aluminum
(53) AWS D1.2, Structural Welding Code—Stainless
Steel
(54) AWS D10.11, Recommended Practices for Root
Pass Welding of Pipe Without Backing
arc preheating. An arc that does not melt the base metals
is sometimes used to remove the chill or significantly
raise the temperature of the weld joint. This can be used
to remove moisture or light residues of oils. This can be
accomplished by a first pass or a second leading arc.
arc welding torch. A device used to transfer current to a
fixed welding electrode, position the electrode, and
direct the flow of shielding gas.
automatic welding. Welding with equipment that requires
only occasional or no observation of the welding, and
no manual adjustment of the equipment controls.
backing or back-up bars. Plates or bars that are in contact with the workpieces on either the root or the face
side of the welds should be located so as not to contaminate the weld or base metal or cause gas or flux
(if used) entrapment. These accessories are usually
made of copper or stainless steel.
2.3 ISO Standards11
(1) ISO6848, Tungsten Electrodes for Inert Gas
Shielded Arc Welding, and for Plasma Cutting and
Welding.
brace-technique. A technique used in manual welding of
vessels, sheet metal and structures. In this welding technique, the welder stabilizes the torch by resting his wrist,
arm or elbow as far away from the weld zone as possible
and sliding the wrist in the direction of welding.
2.4 OSHA Standards12
(1) Code of Federal Regulations (OSHA), Title 29
Labor, Parts 1910.1 to 1910.1450
direct current electrode negative (DCEN). The
arrangement of direct current arc welding leads in
which the electrode is the negative pole and the workpiece is the positive pole of the welding arc.
3. Definitions
direct current electrode positive (DCEP). The arrangement of direct current arc welding leads in which the
electrode is the positive pole and the workpiece is the
negative pole of the welding arc.
The terms and definitions are divided into two
categories:
(1) general welding terms (highlighted by bold print)
compiled by the AWS Committee on Definitions and
Symbols (which can be found in the latest AWS A3.0,
Standard Welding Terms and Definitions); and,
(2) terms or definitions (highlighted by bold italics)
defined by the AWS C5C Subcommittee on Gas Tungsten Arc Welding, which are defined as they relate to this
Recommended Practice, or are additions or modifications to AWS A3.0 terms or definitions.
dragging-the-finger. A technique used in manual welding of all types of joint configurations. It can be used
when welding all diameters of pipe and tubing. In this
welding technique a fingerstall is made by overlapping a “sleeve” of fiberglass material approximately 8 in. [200 mm] long. The fingerstall is placed
over the middle finger and should extend approximately 1 in. [25 mm] beyond the end of the finger.
The fingerstall is used to stabilize the hand holding
the torch as it is slid along during welding.
air cooled torch. A nonstandard term for a gas-cooled
torch.
arc postheating. The intense heat of an arc can be used
to reduce the cooling rate of a weld after a fusion weld
has been made. This is primarily a nonmelting pass.
dressing pass. The weld bead shape can be changed or
improved by the use of a cosmetic pass after the weld
has been completed. This is primarily accomplished
by remelting of the solidified weld bead surface. This
is frequently accompanied with transverse oscillation
of the arc or torch. Sometimes a small amount of filler
metal is added.
11. Available through ISO Central Secretariat, International
Organization for Standardization (ISO) 1, rue de Varembé,
Case postale 56, CH-1211 Geneva 20, Switzerland; Online:
http://www.iso.ch/iso/en/ISOOnline.frontpage.
12. Available through U.S. Government Printing Office, Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA
15250-7954.
electrode holder. A device used for mechanically holding and conducting current to an electrode during
welding. See arc welding torch.
7
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
fixture. A device designed to hold and maintain parts to
be joined in proper relation to each other.
run-off weld tab. Additional material that extends
beyond the end of the joint, on which the weld is
terminated.
freehand technique. The free hand technique is a
method where welding is accomplished without the
benefit of stabilization of hand and welding torch. It is
the most difficult way to effect a weld and is not recommended unless no other option is available.
run-on/off tabs. Additional material (devices) used
mostly on butt and lap joints to facilitate starting and
extinguishing the arc.
semiautomatic welding. Manual welding with equipment that automatically controls one or more of the
welding conditions.
gas cup. A nonstandard term for gas nozzle.
gas nozzle. A device at the exit end of the torch that
directs shielding gas.
straight polarity. A nonstandard term for direct current
electrode negative.
gas tungsten arc welding (GTAW). An arc welding
process that uses an arc between a tungsten electrode
(nonconsumable) and the weld pool. The process is
used with shielding gas and without the application of
pressure. Filler metal may or may not be used.
tandem arcs. To increase the speed or increase penetration in single pass welds, closely spaced arcs can be
employed. Two to five arcs in tandem can be
employed with three arcs common. This multiple arc
process is primarily employed for high-speed tube or
pipe welding. It can also be employed for sheet and
plate splicing.
Heliarc® welding. A nonstandard term for gas tungsten
arc welding. It refers to the earliest use of the process
when only the inert gas helium was utilized as the
shielding method.
tooling. Weld tooling can be a variety of devices (fixtures) that are associated with the welding operation
and their use assists in producing a weldment that
meets all specified requirements. Weld joint backing
and/or chill bars are examples of weld tooling.
hold down and backing bars. Fixtures which provide the
means to clamp and position the weldment, and supply backing support and/or shielding gas to the underside of the weld bead. Backing bars usually contain
passages to facilitate inert gas purging. When grooved
backing bars are used, the grooves should be shallow
to minimize melt through and to limit the height of
root reinforcement. Grooves in backing bars should
have rounded corners to be elliptical in shape to prevent entrapments and to minimize stress raisers relative to underbead shape. These devices usually extend
the full length of the weld.
torch. See arc-welding torch.
tungsten-arc welding. A nonstandard term for gas tungsten arc welding.
tungsten electrode. A non-filler metal electrode used in
arc welding, arc cutting, and plasma spraying, made
principally of tungsten.
tungsten inert gas (TIG) welding. A nonstandard term
for gas tungsten arc welding. It refers to the early
use of the process when only the inert gases argon and
helium were utilized as the shielding method.
machine welding. A nonstandard term when used for
mechanized welding.
walking-the-cup. A technique for manipulating the torch
when manually welding groove and fillet welds. With
this technique, the electrode extension is adjusted to
allow the proper arc length while the edge of the cup
rests on the side of the joint. The torch is manipulated
in a manner to swing the tip of the tungsten back and
forth across the side of the joint by “walking-the-cup”
on each edge of the joint. The left or right edge of the
gas nozzle/cup is in constant contact with the members giving the cup a walking motion on the weld
joint.
manual welding. Welding with the torch held and
manipulated by hand. Accessory equipment, such as
part motion devices and manually controlled fillermaterial feeders may be used.
mechanized welding. Welding with equipment that
requires manual adjustment of the equipment controls
in response to visual observation of the welding, with
the torch held by a mechanical device.
opposing arcs. This is a welding process employing two
arcs. Each arc is located on opposite sides of the weld
joint. The purpose is to equalize stresses on plates to
reduce the tendency for warping or distortion.
welding fixture (also see fixture). A device designed and
built to hold parts to be joined in proper relationship
with each other. Chill bars are often used to help cool
the weld area rapidly and usually result in controlling
weld shrinkage and workpiece distortion.
reverse polarity. A nonstandard term for direct current
electrode positive.
8
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
The other method involves touch or contact starting where the tungsten electrode is brought in contact
with the base metal and then withdrawn to initiate the
arc. The electrode is then retracted to the proper arc gap.
4. GTAW Principles
4.1 Process Description. The GTAW process and equipment are illustrated in Figures 7 and 8. GTAW produces
fusion (coalescence caused by melting) of base metals
from the heat generated by an electric arc. The arc is established between the tip of a nonconsumable tungsten or
tungsten alloy electrode and the workpiece (also called
base metal). The electrode is held in an arc welding
torch, either water-cooled or gas-cooled, through which
shielding gas is fed. The shielding gas provides the required arc characteristics by becoming a plasma (ionized), and also shields the electrode, filler metal end, and
the molten weld pool from contamination by the atmosphere. Once the arc and weld pool are established, the
torch is moved along the joint and the arc progressively
melts the faying surfaces (surfaces to be joined). Filler
wire, when used, is added to the weld pool to fill the
joint. Filler wire is usually added to the leading edge of
the weld pool, but may be added to the trailing edge, or
both.
To avoid weld contamination, the nonconsumable
electrode requires special arc initiation techniques. There
are two main methods utilized.
One method involves arc starters such as highfrequency generators or capacitor discharge starters,
which provide a high voltage across the arc gap. This
causes the shielding gas to ionize and thus makes it conductive, allowing the arc to initiate.
Note: It is considered good practice, when the touch
starting system is used, to initiate the arc in a location
that will be consumed in the subsequent weld metal. The
initiation point is termed an arc strike or arc burn and, if
visible after welding, is cause for rejection by a number
of specifications.
The GTAW process is adaptable to manual, semiautomatic, mechanized, and automatic applications. It
can be used to produce continuous welds, intermittent
welds, and spot welds. Unlike other arc welding processes, the GTAW process can be used to produce autogenous (no filler wire) welds because the electrode is
nonconsumable. For many applications, the addition of
filler wire is desirable or necessary.
The process can be used to produce welds on essentially all joint designs and geometries. It can be used to
weld a wide range of thicknesses and sizes of plate,
sheet, pipe, tube, and other structural shapes. The GTAW
process can be successfully used in any welding position.
4.2 Process Advantages. GTAW has become indispensable as a tool for many industries. If properly utilized, the
GTAW process will produce the high quality welds required for the aerospace, nuclear, pharmaceutical, semiconductor and other industries. As illustrated in Figure 9,
weld beads produced with the GTAW process typically
are cleaner than with any other arc welding process because no slag or spatter is present. Visual and nondestructive inspecting of GTAW welds is thus easier.
The combination of GTAW for root pass welding with
either shielded metal arc welding (SMAW) or gas metal
arc welding (GMAW) for the fill passes is particularly
advantageous for welding pipe. The GTAW process
produces a smooth, uniform root pass weld while the fill
passes are made with a higher deposition rate (more
economical) process. Table 1 presents an overview of
GTAW, GMAW, and SMAW processes for different base
materials.
The following are some advantages of the GTAW
process:
(1) capable of producing superior quality welds, generally free of defects
(2) is free of the spatter which occurs with most other
arc welding processes
(3) can be used with or without filler metal as
required for the specific application
(4) allows excellent control of root pass weld
penetration
(5) can produce inexpensive autogenous welds at high
speeds
Figure 7—Stylized Representation of the
Gas Tungsten Arc Welding Process
9
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 8—Gas-Cooled GTAW Torch and Stylized Representation
of Typical Gas Tungsten Arc Welding Equipment
10
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
(6) can use inexpensive power sources
(7) allows precise control of the welding variables
(8) is very good for joining thin base metals because
of the excellent control of heat input
(9) can be used to weld almost all metals, including
dissimilar metal joints
(10) is especially useful for joining aluminum and
magnesium, which form refractory oxides
(11) is probably the most used process for reactive
metals like titanium
(12) allows the heat source and filler metal additions to
be controlled independently
4.3 Process Limitations. The GTAW process requires
continuous and efficient weld metal shielding. Backup
shielding or enclosed shielding is also required in many
applications. This basic requirement tends to limit the
process to indoor types of applications. However, with
proper shielding techniques, field (outdoor) welding is
also readily accomplished.
Figure 9—Clean Weld Beads
Typical of Properly Shielded
GTAW Welds
Table 1
Welding Process Comparison Based on Quality and Economics
Welding Processes(1) and Ratings(2) (All Positions)
Applications
Carbon steel plate >3/16 in. [5 mm]
Carbon steel sheet d3/16 in. [5 mm]
Carbon steel structural
Carbon steel pipe d3 in. [75 mm] IPS
Carbon steel pipe >3 in. [75 mm] IPS
Stainless steel plate >3/16 in. [5 mm]
Stainless steel sheet d3/16 in. [5 mm]
Stainless steel pipe d3 in. [75 mm] IPS
Stainless steel pipe >3 in. [75 mm] IPS
Aluminum plate >3/16 in. [5 mm]
Aluminum sheet d3/16 in. [5 mm]
Aluminum structural
Aluminum pipe d3 in. [75 mm] IPS
Aluminum pipe >3 in. [75 mm] IPS
Nickel and nickel alloy sheet
Nickel and nickel alloy tubing
Nickel and nickel alloy pipe d3 in. [75 mm] IPS
Nickel and nickel alloy pipe >3 in. [75 mm] IPS
Reactive metals—titanium—sheet, tubing, pipe
Refractory metals—Ta and Cb—sheet, tubing
GTAW
GMAW
SMAW
G
E
F
E
G
G
E
E
G
G
E
E
E
E
E
E
E
E
E
E
E
E
F
F
G
E
G
F
G
E
G
G
NR
F
F
NR
F
F
NR
NR
E
G
E
F
G
G
F
F
F
NR
NR
NR
NR
NR
F
NR
NR
NR
NR
NR
Notes:
(1) GTAW = Gas Tungsten Arc Welding (TIG).
GMAW = Gas Metal Arc Welding (MIG).
SMAW = Shielded Metal Arc Welding (Stick).
(2) E = Excellent, G = Good, F = Fair, NR = Not Recommended on basis of cost, usability, or quality.
11
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
4.3.1 Limitations. The following are some limitations
of the GTAW process:
(1) Deposition rates are lower than the rates possible
with the consumable electrode arc welding processes unless used with hot-wire additions. Therefore, it can be
less economical than the consumable electrode arc welding processes for thicker sections (greater than 3/8 in.
[10 mm]).
(2) For manual welding, there is a need for slightly
more dexterity and welder coordination than with gas
metal arc welding or shielded metal arc welding.
(3) Shielding the weld zone properly in drafty environments is difficult.
change weld pool fluid flow. If present in low levels (less
than 30 parts per million [ppm]) in these materials, increasing arc current can produce a dramatic increase in
weld width without much increase in penetration. If sulfur content is greater than 50 ppm, an increase in arc current can produce a dramatic increase in penetration.13, 14
4.4.1.1 Current Polarity. Three basic categories
of welding current are available: direct current (DC),
alternating current (AC), and programmed current. Programmed current is a category combining some of the
features of AC and DC. Variable polarity (VP) can be
considered as a subset of programmed current and is
replacing AC and balanced AC in many applications.
There are two polarities or directions in which the current can flow in the welding circuit; direct current electrode negative [DCEN, so-called straight polarity, see
Figure 10(A)] and direct current electrode positive [DCEP,
so-called reverse polarity, see Figure 10(B)]. When using
direct current, the tungsten electrode may be connected to
either the negative or positive terminal of the power source.
When the electrode is negative (cathode), the electrons
flow from the electrode to the work and the ions move
from the work to the electrode. When the electrode is positive (anode), the electrons flow from the work to electrode
and the ions move from the electrode to the work. The
choice of whether to use DC, AC, VP, or programmed current depends largely on the material to be welded.
4.3.2 Potential Problems. Potential problems with
the process include:
(1) Tungsten inclusions can occur if the electrode is
allowed to contact the weld pool or if the electrode is
overheated.
(2) Contamination of the weld metal can occur if
proper shielding of the filler metal by the gas stream is
not maintained or if the torch shielding gas does not
properly protect the weld pool.
(3) There is low tolerance for contaminants on filler
or base metals.
(4) Possible contamination or porosity can be caused
by coolant leakage from water-cooled torches, as with
other processes.
(5) Arc blow or arc deflection can be a concern, as
with other arc welding processes.
4.4.1.2 Direct Current with Respect to Polarity.
The two types of direct current GTAW to be considered
are direct current electrode negative (DCEN), and direct
current electrode positive (DCEP). Each type has its own
characteristics and areas of application.
Direct current electrode negative (DCEN) when combined with a thermionic electrode (e.g., tungsten) generates approximately 70% of the heat at the anode (work)
and approximately 30% of the heat at the cathode (electrode). Since DCEN produces the greatest amount of
heat at the workpiece, this offers the advantage of deep
penetration and fast welding speeds. DCEN is the most
common configuration used in GTAW, and is used with
argon, helium, or a mixture of gases to weld most metals.
Helium and helium mixes are frequently the gases of
choice for mechanized welding because of helium’s
higher thermal conductivity. Additions of helium or hydrogen to argon are also frequently used for mechanized
welding because these produce a “hotter” arc.
4.4 Process Variables. The primary variables in GTAW
are welding current, arc voltage (arc length), travel speed,
electrode (condition, shape, and alloy), and shielding gas.
Additional input parameters include wire feed rate, electrode orientation, travel angle, arc deflections (magnetic
and mechanical arc oscillations), and pulsing parameters.
The main issue that these variables affect is the energy
transferred from the power source through the arc and
into the work, and the rate and control of that energy
transfer. Variation in chemical composition of the base
metal and filler metals as well as condition of the joint
design, joint preparation (including fixturing and tooling), and welding position must also be considered.
4.4.1 Arc Current. Weld penetration is directly proportional to arc current, i.e., as the current is increased,
the weld penetration increases. Arc current also effects
the voltage as a function of the power source characteristic and from the forces (pressure, Lorentz, buoyancy) acting on the weld pool to change the pool’s position under
the arc. For this reason, it is necessary to change the voltage setting when the current is adjusted to keep a fixed
arc length in automatic welding. For some materials, such
as stainless steels and nickel alloys, certain trace elements
(such as sulfur and oxygen) alter the surface tension and
13. Burgardt, P. and Campbell, R., 1992, Chemistry Effects on
Stainless Steel Weld Penetration, Ferrous Alloy Weldments,
Trans Tech Publications, Switzerland.
14. Burgardt, P., and Heiple, C., Interaction Between Impurities and Welding Variables in Determining GTA Weld Shape,
Welding Journal, Vol. 65, No. 6, June 1986, pp. 150-s–155-s.
12
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
CURRENT TYPE
DCEN (A)
DCEP (B)
AC Balanced/Variable Polarity
(Programmed) (C)
ELECTRODE POLARITY
Negative
Positive
Negative and Positive
No
Yes
Yes, Once Every Half Cycle
70% at Work 30% at Electrode
30% at Work 70% at Electrode
50% at Work, 50% at Electrode
(Varies with Program Setting)
Deep, Narrow
Shallow, Wide
Medium
Excellent, e.g., 1/8 in. [3 mm]:
400 A
Poor, e.g., 1/4 in. [6 mm]:
120 A
Good, e.g., 1/8 in. [3 mm]:
225 A
OXIDE CLEANING ACTION
HEAT BALANCE IN THE
ARC (APPROXIMATE)
PENETRATION
ELECTRODE CAPACITY
Figure 10—Characteristics of Current Types Used for Gas Tungsten Arc Welding
With direct current electrode positive (DCEP), a cathodic cleaning action is created at the surface of the
workpiece. This cathodic cleaning at the work surface
can be beneficial in removing oxides present on the surface of some metals. In practice, this method is not used
as frequently as DCEN, AC, or Variable Polarity (VP)
because of the overheating of the electrode that occurs,
but it does have a particular advantage of surface cleaning on metals whose oxides cause problems to the welding operation. For example, this cleaning action is
beneficial for the welding of aluminum and magnesium.
This same action occurs in the reverse polarity half cycle
of AC and VP welding. In practice, alternating current
(AC) or variable polarity (VP) schemes are usually used
when cathodic cleaning action is needed.
Unlike DCEN, in which the electrode tip is cooled by
the evaporation of electrons, when the electrode is used
as the positive pole (i.e., DCEP), its tip is heated by the
bombardment of electrons as well as by its resistance to
their passage through the electrode. Therefore, to reduce
resistance heating and increase thermal conduction into
the electrode collet, a larger diameter electrode is required for a given welding current when using DCEP
(reverse polarity) to reduce electrode tip melting. DCEP
is sometimes used for thin cross sections to reduce heat
input.
4.4.1.3 Alternating Current with Respect to
Polarity. The condition existing when the welding current polarity is periodically alternated from electrode
positive to electrode negative is called alternating current
[AC, see Figure 10(C)]. AC combines the work cleaning
action of electrode positive (reverse polarity) with the
deep penetration characteristic of electrode negative
(straight polarity).
Conventional AC welding power sources produce a
sinusoidal open circuit voltage output. When changing
from positive to negative flow, the current must pass
through zero, which extinguishes the arc. The arc must
then be reignited or it will remain extinguished.
13
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 11—Relationship Between Arc Pressure and Pulse Frequency
In pulsed DC welding, the peak current level is typically set at 2 to 10 times the background current level.
This condition provides the benefits of the driving, forceful arc characteristics of high current with the low heat
input of low current. The pulse current is used to obtain
the good fusion and penetration while the background
current maintains the arc and allows the weld area to cool
and/or solidify. Low-frequency DC pulsing of the weld
current can be thought of as a moving series of overlapping spot welds.
Some means of maintaining the arc during the voltage
reversal is required with conventional sinusoidal welding
power sources. This has been done by using high open
circuit voltage power sources; by discharging capacitors
at the appropriate time in the cycle; by using highvoltage high-frequency generators in parallel with the
arc; and by using power sources with a square wave
output.
4.4.1.4 Pulsed DC Welding. Pulsed GTAW is
characterized by a repetitive switching between a peak
(high) current and a background (low) current. Alternate
melting and solidification are obtained by switching between high and low currents. The high (peak) current
(5 A–200 A) is normally higher than continuous DC
welding to ensure rapid full penetration, after which
switching to a low (background) current (1 A–15 A) allows the molten pool to solidify but maintains a pilot arc
for application of the next pulse.15
There are three broad categories of pulsing: low frequency (0.5 Hz–20 Hz), sometimes called “thermal pulsing”; intermediate frequency (>20 Hz–500 Hz); and,
high frequency (>500 Hz up to 16 kHz or more).
There are several advantages of pulsed current. The
effect of high-frequency switching is to produce a “stiff”
welding arc. Arc pressure is a measure of arc stiffness.
As shown in Figure 11,16 as the switching frequency
nears 10 kHz, arc pressure increases to nearly four times
that of a steady DC arc. As arc pressure increases, there
is a reduced effect by magnetic fields (such as arc blow),
shielding gas movement (wind), etc.
For a given average current level, greater penetration
can be obtained by pulsing the current compared with
continuous current. This is useful on metals sensitive to
16. Refer to AWS Welding Handbook, 8th Edition, Volume 2:
Welding Processes, Chapter 3, “Gas Tungsten Arc Welding,”
Figure 3.12, and p. 86 for more information.
15. Pulsed Arc Welding. J. A. Street, Abington Publishing,
p. 11, (1990).
14
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 12—Programmed (Modulated) Current without Polarity Reversal
heat input and for distortion control. Also, because there
is insufficient time for significant heat flow during the
current pulse, metals of vastly dissimilar thickness respond nearly equally and thus nearly equal penetration
can be achieved. For a similar reason, very thin metals
can be joined with pulsed DC. In addition, one set of
welding parameters can be used on a joint in all positions, such as a circumferential weld in a horizontal pipe.
Pulsed DC is also useful for bridging gaps in open root
joints and for welding with consumable inserts. A disadvantage of pulsed DC current is that the welding power
source and controller are more sophisticated and relatively more expensive.
4.4.1.5 Programmed Current. Welding power
sources have also been developed that are capable of providing various types of modulated current with or without actual polarity reversal. See Figure 1217 for an
example. These current pulsation techniques have been
17. References: AWS Welding Handbook, 8th Edition, Volume
2: Figure 3.10, p. 85; Muncaster, Figure 4.2, p. 37.
15
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 13—Characteristics of Variable Polarity (Programmed) Weld Current
developed to increase weld penetration, to reduce heat
input, and to control or improve weld root and bead contour, grain size, and out-of-position welding capabilities.
Two such programmed current techniques are square
wave AC pulsation and pulsating DC. Variable polarity
can be thought of as a subset of programmed current.
directly proportional to the arc length, while the pool
depth is inversely proportional to the arc length. Therefore, in most applications the desired arc length is as
short as possible.
4.4.3 Travel Speed. Travel speed affects both the
width and penetration of a gas tungsten arc weld. However, its effect on width is more pronounced than on penetration. Travel speed is important because of its effects
on cost and weld quality.
High travel speeds minimize distortions caused by
thermal expansions and contractions during welding. On
the other hand, alloys prone to cold cracking are usually
not welded at high speeds, since the associated steep thermal gradients and rapid cooling rates would contribute to
crack formation. Lower welding speeds are applied to circumvent this cracking problem (often used in combination with preheating the base metal to further reduce the
possibility of cold cracks and decrease the cooling rates).
4.4.1.6 Variable Polarity. The term variable polarity describes an alternating welding current that is asymmetrical about the zero current level. This is shown in
Figure 13. The symmetry of the current above and below
zero is controlled by the current balance adjustment on
the power source.
The variable polarity power source was developed to
meet the criteria established for effective plasma “keyhole” welding of aluminum, especially in heavy sections.
While primarily used for plasma arc welding (PAW) it
also is used for certain GTAW applications. This direct
current (DC) machine produces cyclic changes of DCEN
and DCEP polarities with independent control of the current amplitude and the duration.
4.4.4 Electrodes. The shape of the tungsten electrode
tip is an important process variable in GTAW. The tungsten electrodes may be used with a variety of tip configurations and preparation methods. Electrode tip
configuration is a welding variable that should be studied
during the welding procedure development. It is important that consistent electrode geometry be used once a
welding procedure has been established. Changes in
electrode geometry can significantly influence the weld
bead shape and size as shown in Figure 14.18
4.4.2 Arc Voltage. The voltage measured between the
tungsten electrode and the work is commonly referred to
as the arc voltage. The arc voltage is changed by the effects of the other variables, and is used in describing
welding procedures only because it is easy to measure.
Since the other variables such as the shielding gas, electrode, and current have been predetermined, the arc voltage becomes a way to control the arc length. The arc
length is a critical variable that is difficult to monitor
without appropriate equipment. Arc length is important
with this process because it affects the width and depth
of the weld pool. The arc voltage is a function of gas
composition and arc gap length. The weld width is
18. Reference: Key, J., “Anode/Cathode Geometry and Shielding Gas Interrelationships in GTAW,” Welding Journal, Vol. 59,
No. 12, Dec. 1980, Figure 1, p. 265-s.
16
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 14—Arc Shape and Fusion Zone Profiles as a Function of
Electrode Tip Geometry in Pure Argon Shielding Gas
4.4.5 Shielding Gas. As mentioned previously, the
shielding gas has several influences on the GTAW process. Attention should be paid to the gas quality (purity),
to its voltage-current characteristic, and to its thermal
conductivity. Shielding gases will be covered in detail in
Section 7.
In mechanized or automated welding the electrode
(torch) angle can be an important parameter to counter
the effects of arc drag or to force changes to the shape of
the pool (and thus change the resultant solidification) by
redirecting the arc force either into or away from the
direction of travel.
4.5 Related Variables. A number of variables can have
a pronounced effect upon GTAW quality and speed.
These include filler metal (type, size, feed mechanism),
joint design, material composition, and tooling. In addition, electrode orientation and arc deflections must be
considered.
4.5.2 Arc Motion and Deflections. Several variations
of arc deflection have been applied in attempts to modify
the resultant fusion zone, including grain refinement.
These techniques include weld pool stirring, arc oscillations and arc modulations/pulsations. One of the more
popular techniques is magnetic arc deflections or oscillations. The application of one or more magnetic poles is
used to stabilize the arc column and minimize the effects
of local magnetic disturbances that result in arc blow.
Fixed and/or variable electromagnetic poles have been
applied in a similar manner to stabilize or to oscillate the
arc column. Stable arc deflections can be used to counter
the effects of arc drag during higher speed welding.19
4.5.1 Electrode to Work Angle and Position. The
forces exerted on the weld pool vary with the angle of the
torch (electrode) with respect to the vertical and the direction of travel.
In manual welding the welder may use this to:
(1) Properly distribute weld deposit relative to the
joint being welded, e.g., fillet or groove weld.
(2) Affect multipass or stringer beads that may overlap one another.
(3) Control the amount of weld penetration or drop
through (root reinforcement) and/or weld bead shape.
19. Hicken, G. K. and Jackson, C. E., 1966, “The Effects of
Applied Magnetic Fields on Welding Arcs,” Welding Journal,
Vol. 45, No. 11, Nov. 1966, pp. 515-s–524-s.
17
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Another variation of arc deflection is the weaving or
mechanical motion of the torch (electrode) side to side,
to be sure that a full fusion weld is achieved.
source are a compromise of cost, weight, size, type of
input or primary power, performance, and the type of
current to be used in the welding process.
Selecting the correct power source, of course, depends
upon process requirements. The first step is to determine
the electrical requirements of the welding process with
which it will be used. Other factors to consider include
such things as future requirements, maintenance, economic considerations, portability, environment, available
skills, safety, manufacturer’s support, code compliance,
and standardization. Most electronically controlled power
sources offer rapid dynamic response; i.e., can change
from one level to another. As a result, these power sources
can be used to provide pulsed welding current. Series linear regulator and switched secondary designs provide DC
welding current from rectified single or three-phase input
power. Silicon controlled rectifier (SCR) designs can provide AC and DC current from single-phase power and DC
current from three-phase power. Depending on the design, inverter power sources can provide AC and DC output from single or three-phase input power. Inverter
power sources are the most versatile, with many offering
multi-process capabilities and variable welding current
waveform output. Inverters are also lighter and more
compact than standard 60 Hz transformer-rectifier power
sources of equivalent current rating.
5. Equipment and Supplies
5.1 Welding Power Sources (Used for GTAW)—Introduction. Constant-current type power sources are normally used for GTAW. Power required for both AC
(alternating current) and DC (direct current) GTAW can
be supplied by inverter, transistor, or transformerrectifier power sources or from rotating AC or DC generators. A description of the types of currents is found in
Section 4. Advances in semiconductor electronics have
made transformer-rectifier, and more recently, transistor
and inverter type power sources popular for both shop
and field GTAW. Engine driven power sources continue
to be widely used in the field.
In constant current power sources the weld current remains nearly constant with variations in output voltage,
as shown in Figure 15. It is the goal of the power source
manufacturer to provide power sources that produce the
desired type of current (e.g., DC, pulsed DC, AC, etc.)
and maintain the current at the desired level regardless of
external influences such as power line voltage fluctuations. The components used for each type of power
Figure 15—Typical Volt-Amp Characteristic Curves for GTAW Power Sources
18
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
It is important to select a GTAW power source based
on the type of welding current required for a particular
application. The types of welding current include AC
sine wave, AC square-wave, DC, and pulsed DC. The
following sections have more information on the types of
power sources. Many power sources are available with a
variety of additional controls and functions such as water
and shielding gas control, wire feeder and travel mechanism sequencing, current up-slope and down-slope, and
multiple-current sequences.20, 21
currents are the major determining factors in the voltages
and currents that each of these devices generate.22
5.1.3 Transistorized Power Sources. The transistorized power source derives its name from the fact that the
output of the welding power source utilizes transistors.
The transistorized source takes the DC created by a
transformer and diodes and uses the transistors to control
the power source output current. The use of transistors
allows for very fast and precise control of the output current, which is especially advantageous in pulsed GTAW
applications. The two common types of transistorized designs are referred to as series linear regulators and secondary switchers.
The transistorized power source has a very stable output and is fast to respond to control signals. Advanced
design methods make it possible to obtain a modulated
signal whereby the output current is proportional to the
input control voltage. The fast response of the power
source when combined with the modulation capability
makes it possible to generate sine wave, thermal pulsed
DC, and high-frequency pulsed DC all from the same
power source by simply changing the input control voltage or modulation signal.
5.1.1 Transformer Rectifier Power Sources. One of
the most common types of GTAW power sources utilizes
transformers and some form of rectification. The rectification can be provided by simple inexpensive diodes or
SCRs. The purpose of the transformer in this power
source design is to reduce the incoming line voltage and
increase the current to a level that is more closely needed
for the welding process. For example, a welding power
source using 480 V supply voltage needs to be reduced to
a voltage in the range of 30 V–80 V, and the current is
increased proportionally to the reduction in voltage. Single rectifiers, also known as diodes, can be connected to
create a single polarity of voltage, i.e., direct current. The
SCRs are simply controllable diodes that improve the
ability of the electronics to control current. Prior to the
use of SCRs this type of control had been accomplished
using mechanically driven magnetic control techniques
and saturable reactor magnetic controls. The magnetic
type of control was relatively slow and had many mechanically related deficiencies.
5.1.4 Inverter/Converter Power Sources. The inverter power source was originally developed for the
military to provide significant reduction in weight and
size of the power source relative to the other types of
sources described thus far in this text. The welding inverter power source provides a weight reduction factor of
4 to 5. The inverter design is also electrically more efficient and the output more stable than SCR power source
design technologies. This is primarily accomplished by
the reduction of the transformer size. This reduction in
transformer size is possible by increasing the frequency
used in the transformer section. The transformer section
of the inverter power source is utilized in the many thousands of Hertz as opposed to 60 Hz in other power source
designs.
The inverter power source is a type of GTAW power
source that takes AC input power, typically at 60/50 Hz,
and changes it to DC, which is converted to higher frequency AC and then rectifies the higher frequency AC to
obtain the desired output current. Several variations of
the inverter design are available. An example of the
design schematic is shown in Figure 16. This higher
frequency is in the range of 1 kHz–125 kHz. The size of
a transformer is indirectly proportional to the frequency
of the voltage. That is, as the frequency increases the size
5.1.2 Generator Power Sources. Generators are
most commonly used for field applications or in industrial settings where sufficient power is not available from
the existing power system (mains). The generator-type
power sources convert mechanical energy into electrical
power suitable for arc welding. The mechanical power
can be obtained from an internal combustion engine, an
electric motor, or from a power take-off from other
equipment. For welding, two basic types of rotating
power sources are used: the generator and the alternator.
Both have a rotating member normally called a rotor or
an armature, and a stationary member, called a stator. A
system of excitation is needed for both types. Alternators
are used to produce alternating currents while generators
are used to produce direct currents. The speed of rotation, the winding configuration and external excitation
20. Refer to AWS Welding Handbook, 8th Edition, Volume 2:
Welding Processes, Chapter 1, “Arc Welding Power Sources,”
for more detailed information.
21. Grist, F. J., Farrell, W. and Lawrence, G. S. 1993. Power
Sources. ASM Handbook, 9th Edition, Volume 6, Welding,
Brazing and Soldering, pp. 36–44.
22. For additional information, see AWS Welding Handbook,
8th Edition, Volume 2: Welding Processes. Also see ASM
Handbook, 9th Edition, Volume 6: Welding, Brazing, and
Soldering.
19
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 16—Typical Inverter Power Source Components
and weight of a transformer decreases. Since the voltage
being transformed is very high in frequency, the size of a
transformer is significantly less, as noted above, when
compared to a transformer for the same application used
at 60 Hz. Thus significant size and weight reduction is
possible. The inverter power source also has a very fast
response time compared to many other types of power
sources, e.g., transformer-rectifiers. The fast response
time is useful in pulsed welding applications.
measured and controlled, but rather the major process
variables that affect heat input and torch position are
measured. Control of the process variables improves process consistency, but does not ensure consistent welds
under all conditions.
Although the actual weld characteristics cannot typically be controlled, it is possible to precisely control a
majority of the process variables that drastically affect
weld quality and consistency (repeatability). These
variables include arc voltage, weld current, travel speed,
wire feed speed, shielding gas flow, and multiple axes of
position.
There are two categories of controls used in most
GTAW processes. The first is the open loop control system. In the open loop control system the process variable
is generated and no corrections are made to this setting to
maintain the desired set point, even if the output value is
not correct. A closed loop control assures the set point
value is maintained regardless of the outside influences.
A sensor measures the process variable and sends this
signal back to the comparison circuitry, i.e., feedback.
The circuitry compares the actual variable value to the
desired set point (reference) value. If the actual value is
lower than the reference value then the signal to correct
is increased. This process continues until the reference
value is achieved. The ability to maintain a process variable at the desired or set point value, however, is greatly
affected by whether or not the system is governed by
open or closed loop control methods.
Besides the open loop and closed loop control methods, either of these types of control can be based on analog or digital principles. The analog controller typically
5.2 Controllers. The term controller is used throughout
industry and has many meanings. In the welding field
there are two common types of controllers. The first is
the controller used to control a single process variable.
The second type of controller is the weld sequence controller that orchestrates all of the individual process variables so that each weld variable is set to the proper level
at the proper time during the weld cycle.
The most common weld sequence controller is time
based. That is, the control is programmed in time relative
to the arc start or the pre-flow of electrode shielding gas.
It is also possible to have a position based weld sequence
controller. In this type of controller the sequencing of the
process variables is determined or programmed using the
relative position or location of the torch with respect to
the part, e.g., a change in speed.
5.2.1 General Control Concepts. Each process variable in the GTAW process is set to an appropriate level to
produce desired weld characteristics (e.g., the desired
weld width, penetration). The variables that are commonly measured and/or controlled are called process
variables. The desired weld characteristics are not being
20
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
uses “circuitry” to perform the necessary set-point and
output comparisons. Such functions are, in many cases,
easily performed using transistor or integrated circuit designs. In other situations it is more desirable to implement the control functions using digital circuits,
microprocessors, or some other digital computation system such as a personal computer.
In all of the following process variable control discussions it must be remembered that the open loop and
closed loop implementations are possible, and, the control may be implemented using digital or analog techniques or a combination of digital and analog methods.
The following provides a brief discussion of typical individual process variable controls.
The simplest and most common travel speed implementations are the simple linear torch movement or the
constant rotation speed of a part. These are examples of a
single axis of motion. On the other extreme of complexity is the robotic movement of a torch that may involve
many axes of rotation and linear motion to weld a complex part.
5.2.1.4 Wire Feed Speed. For mechanized and
automatic gas tungsten arc welding, wire feeders (see
Figure 17) are often used to deposit filler metal into a
weld joint. The wire must be deposited at a constant volumetric rate so as to not overfill or underfill the weld
joint. The typical wire being fed into the joint by the wire
feeder comes from a supply spool of wire. In most cases,
the wire that is fed to the weld is stiff and the amount of
force needed to uncoil or feed the wire is not constant
during the feeding process. Friction forces inside the
conduit, that guide the wire to the arc, vary considerably
as the conduit is manipulated during the weld process.
Since the force required to feed the wire is not constant, there must be provisions made in the design of
wire feeders to assure constant wire feed rates. In some
of the less expensive designs the speed of the electric
motor used to feed the wire is reduced or the motor speed
is geared such as to achieve mechanical advantage to reduce the effect of the varying force on the speed of the
motor. Feedback control methods can also be used to assure the constant wire feed rate. The latter provides the
best assurance of constant wire feed rate.
As with other controllers, the wire feed rate may be
set using front panel control knobs, signals from computers, or weld sequence controllers. The motors used most
often for this application are DC motors, but digital stepper motors or AC motors can also be used.
For many welding processes the wire feed rate is continuous throughout the welding sequence. That is, the
wire feed rate is maintained at one level throughout the
portion of the welding sequence that requires weld wire.
In thermal pulsed GTAW wire may be fed only during
the peak pulse current time. This requires synchronization of the wire feed command signal to the power source
current control signal. This places additional demands on
the controllers and wire feed motor systems to accomplish this task.
In addition to the speed and synchronization of the
wire feed there are two additional variations for feeding
wire in the GTAW process. These variations are hot and
cold wire feeders as described in more detail in 5.6.
5.2.1.1 Current. The desired current from the
power source is set either using front panel adjustments,
hand or foot controller, or through an external signal that
may come from a computerized weld controller or a dedicated weld sequence controller. If closed loop control is
implemented, a current sensor is used to monitor the actual current that is produced by the power supply.
5.2.1.2 General Motion Control. Motion control
is a general term that refers to control of linear or rotational speed or position, or a combination of these. In
general, for motion to occur there must be some drive
source, such as a motor. If there is feedback involved then
there must be some type of sensor to complete the feedback loop and appropriate electronics for the feedback.
There are three major types of motors used for motion
in GTAW. The first and most common is the DC motor.
The second type sometimes used is the stepper motor.
The stepper motor is a digitally controlled motor and can
be used with or without feedback. The third, and less
common is the AC motor, which is also used for larger
applications.
5.2.1.3 Travel Speed. Travel speed is simply an
implementation of a general motion control, but instead
of using position feedback sensors, a speed or velocity
sensor is used with appropriate modification to the controls to assure that speed is controlled instead of position.
Travel speed in GTAW applications normally refers to
the relative motion between the part and the torch.23 In
many GTAW applications, the part is moved with the
torch remaining in a fixed position. In other cases it is
easier to move the torch with the part remaining fixed.
23. LaCoursiere, E. J., A. H. Farnham, D. G. Howden, L.
Zhang. 1993. “Requirements for High-Speed (GTA) Welding,
Controller Response Time and Speed Resolution,” in the
“International Conference Proceedings on Modeling and Control of Joining Processes,” edited by T. Zacharia, Oak Ridge
National Laboratory. American Welding Society, December 8–
10, 1993, pp. 500–509.
5.2.1.5 Gas. The torch gas flow rate is most often
manually preset using variable area flowmeters, also
commonly known as rotameters. This is the floating ball
in a tube-type indicator commonly seen on welding
equipment. Gas flow is then started and stopped using
21
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 17—Typical Wire Feeder
electrically controlled solenoid valves. The solenoid
valves are most often activated at the appropriate time by
the weld sequence controller. The flow rate is adjusted
manually on most variable area flowmeters. Flowmeters
that can be preset are available. In cases where it is desired to actually measure or control gas flow, controllers
are available for this purpose. The most common of these
is the mass flow meter and controller. For reasons of
cost, it is not common to use mass flow meters and controllers except for cases where flow rates must be remotely controlled or for the most accurate control of
flow.
AVC a hunting or continual adjustment of the arc length
will occur. Some manufacturers provide an additional
option for AVC to prevent this unwanted variation, unless some electronic filtration is used. The option allows
the controller to measure the arc voltage only during the
high or peak current times.
It must be remembered that it is the relationship between arc length and arc voltage that makes the use of
AVC possible. Once a weld is developed, it is assumed
that this relationship will remain constant over time for
production runs. However, many variables can change
the arc voltage vs. arc length relationship. For example,
use of helium provides greater sensitivity than argon gas.
5.2.1.6 Arc Voltage and Arc Length Controllers.
Arc voltage controllers (AVC) can be used in mechanized and automated GTAW welding to maintain arc
length. In this case, the arc itself is the sensor, since its
voltage is a function of its length. A comparison is made
between the actual arc voltage and the desired arc voltage. The difference in voltage is used by the AVC to determine which direction (i.e., closer to or further away
from) and at what speed the welding electrode will be
moved.
5.3 Pulse Controllers. There are numerous types of
pulse controllers available. These may be added to appropriate power sources as an option or integrated as part
of a power source. In either of these cases, the pulse control options may be set and controlled via computer or by
manual selector settings. These controllers provide the
necessary additional controls required to set pulse time,
pulse current, background current and background time
variables.
In pulsed welding the current varies between the peak
and background values. This causes corresponding increases and decreases in arc voltage for a given arc
length. If this fluctuating arc voltage is presented to the
5.4 Weld Sequence Controllers. The weld sequence
controller provides the capability to synchronize the operation of many individual process variable controls so
that the proper weld sequence may occur. For instance a
22
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
weld sequence controller may execute the following
steps:
(1) pre-flow torch gas for 5 seconds,
(2) start the welding arc,
(3) after the arc is successfully started slope the current from 10 amps to 100 amps in ten seconds, etc.
The weld sequence controller can have many forms.
The simplest form is a multi-channel timer that simply
starts the various individual process variable controllers
at the required time. For example, the pre-flow of torch
gas may be started by opening a solenoid valve, the timer
then signals the arc starter, and when the arc is initiated it
simply maintains a current for a predetermined length of
time. In the simplest form, relative torch motion may be
provided manually by the operator.
On the other extreme of capability is the sophisticated
computerized weld controller. This may be a dedicated
microprocessor or computer system. All process variable
control values and functions are handled by this one weld
controller. Figure 18 shows a nonpulsed weld sequence
and Figure 19 shows a pulsed weld sequenced schematic.
5.5 Arc Welding Torches. GTAW torches hold the tungsten electrode, which conducts welding current to the
arc, and provide a means for conveying shielding gas to
the weld zone. Torches are rated in accordance with the
maximum welding current and duty cycle that can be
used without overheating. Most torches are designed to
accommodate a range of electrode sizes and different
types and sizes of gas cups/nozzles. The heat generated
in the torch during welding is removed by shielding gas
cooling and/or water-cooling. Reflected heat can reduce
the duty cycle rating.
5.5.1 Types of Torches. Several types of welding
torches are available and will be briefly described.
5.5.1.1 Gas-Cooled Torches. Gas-cooled torches
(a nonstandard term is air-cooled torches) provide cooling by the flow of a relatively cool shielding gas through
the torch. Gas-cooled torches are limited to a maximum
current of about 200 A at 60% duty cycle. Gas-cooled
torches may be used at high current settings for low-duty
cycles, short weld lengths with frequent starts and stops,
Figure 18—Typical GTAW Sequence for Non-Pulsed DC Welding
23
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 19— Typical GTAW Sequence for Pulsed DC Current and Pulsed Wire Feed
and tacking of heavy materials. A gas-cooled torch is
illustrated in Figure 8.
Water-cooled torches typically use a water-propylene
glycol mixture in a closed system with a recirculator (see
5.5.5 on Water Coolers). This is especially needed for
systems employing high-frequency arc stabilization and
high-frequency arc starts. This reduces mineral build-up
in the torch from tap water, as well as conserving water.
However, tap water is sometimes used when it does not
interfere with the high-frequency system.
A comparison of typical current ratings for gas-cooled
and water-cooled torches is shown in Table 2.25
5.5.1.2 Water-Cooled Torches. Water-cooled
torches are cooled by the continuous flow of water
through passageways in the holder. As illustrated in Figure 20,24 cooling water enters the torch through the inlet
hose, circulates through the torch, and exits through an
outlet hose. The power cable from the power source to
the torch is typically enclosed within the cooling water
outlet hose.
Water-cooled torches are designed for use at higher
welding currents and duty cycles than gas-cooled
torches. Typical welding currents of 300 A to 500 A can
be used, although some torches have been built to handle
welding currents up to 1500 A. Most machine or automatic welding applications use water-cooled torches.
5.5.1.3 Manual Torches. Torches for manual applications have a head angle (angle between the electrode
and handle) of 90°, 100°, or 120°. Torches are also available with adjustable angle heads and straight-line (pencil
type) heads. Manual torches often have auxiliary
switches, valves, and controls built into their handles for
controlling current and shielding gas flow.
24. AWS Welding Handbook, 8th Edition, Volume 2: Welding
Processes, Chapter 3: Gas Tungsten Arc Welding. Figure 3.4,
p. 78.
25. AWS Welding Handbook, 8th Edition, Volume 2: Welding
Processes, Chapter 3: Gas Tungsten Arc Welding. Table 3.1,
p. 77.
24
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 20—Typical Water-Cooled GTAW Torch (Cross-Sectional View)
Table 2
Comparison of Typical Current Ratings for Gas-Cooled and Water-Cooled GTAW Torches(1)
Torch Size
Torch Characteristics
Small
Maximum Current (100% duty cycle), A
200
Cooling Method
Gas
Electrode Diameters accommodated, in. [mm] 0.020 to 3/32 [0.5 to 2.4]
Gas Cup Diameters accommodated, in. [mm]
1/4 to 5/8 [6 to 16]
Medium
Large
200–300
Water
0.040 to 5/32 [1.0 to 4]
1/4 to 3/4 [6 to 19]
500
Water
0.040 to 1/4 [1.0 to 6]
3/8 to 3/4 [10 to 19]
Note:
(1) AWS Welding Handbook, 8th Edition, Volume 2: Welding Processes, Chapter 3, Gas Tungsten Arc Welding, Table 3.1, p. 77.
The welder prefers the lightest torch possible for any
application because of the tiring effects of positioning
and manipulating the torch with relationship to the weld
pool. The angle of the torch head is usually dependent on
the type of welding to be performed. A 120° torch head
is preferred when making fillet welds and a 100° torch
head is preferred when making butt welds. Figure 2126
shows typical GTAW torches.
5.5.1.4 Mechanized and Automated Torches.
The basic mechanized or automatic torch has a straightline (pencil type) head (see Figure 21). The torch is either rotated mechanically around a joint to be welded,
mounted on a tracking device for longitudinal welds or
on a robot for all configuration welds.
5.5.1.5 Orbital Weld Heads. Integral electrode
holders are often used in orbital weld heads. With closedhead types, the electrode is held in a planetary gear housing that rotates around the stationary workpiece (see
26. Photo courtesy of CK Worldwide.
25
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 21—Examples of GTAW Torches
9.4.1.2 for further details). Open head types feature the
torch mounted on a gear that rotates around the workpiece (see Figure 2227). Shielding gases are contained
within the weld head for closed head types and are provided through the torch in open head types.
ramic, fused quartz, lava, or other materials. Ceramic
cups are the least expensive and most popular, but are
brittle and must be replaced often. Fused quartz cups are
transparent and allow better vision of the arc and electrode. However, contamination from metal vapors from
the weld can cause them to become opaque, and they are
also brittle. Water-cooled metal nozzles have longer life
and are used mostly for machine and automatic welding
applications where welding currents exceed 250 A.
5.5.2 Collets. Electrodes of various diameters are secured in the torch by appropriately sized collets or
chucks. Collets are typically made of a copper alloy. The
electrode is gripped by the collet when the torch cap is
tightened in place. Good contact between the electrode
and the inside diameter of the collet is essential for
proper current transfer and electrode cooling.
5.5.3.2 Sizes and Shapes of Gas Nozzles (Cups).
The gas nozzle (cup) must be large enough to provide
shielding gas coverage of the weld pool area and surrounding hot base metal. The gas nozzle diameter must
be appropriate for the volume of shield gas needed to
provide protection and the stiffness needed to sustain
coverage in drafts. A delicate balance exists between the
gas nozzle diameter and the flow rate. If the flow rate for
a given diameter is excessive, the effectiveness of the
shield is destroyed because of turbulence. High flow
rates without turbulence require large diameters; these
are essential conditions at high currents. Size selection
depends on electrode size, type of weld joint, weld area
to be effectively shielded, and access to the weld joint.
5.5.3 Gas Nozzles/Cups. Shielding gases are directed
to the weld zone by gas nozzles, which fit onto the head
of the torch as illustrated in Figure 23. Nozzles are more
often called by the nonstandard term gas cup. Also incorporated in the torch body are diffusers or carefully patterned jets or holes that feed the shield gas to the gas
nozzle (cup). Their purpose is to assist in producing a
laminar flow of the exiting gas shield (see 5.5.3.3 for gas
lenses). Gas nozzles are made of various heat-resistant
materials in different shapes, diameters, and lengths.
These gas nozzles are either threaded to the torch or held
by friction fit.
Suggested gas nozzle sizes for various electrode diameters are covered in Section 6. Use of the smallest gas
nozzle permits welding in more restricted areas, and offers a better view of the weld. However, use of too small
a gas nozzle may cause shielding gas turbulence and jetting, as well as melting of the lip of the gas nozzle.
5.5.3.1 Gas Nozzle/Cup Materials. Shielding gas
nozzles are made of ceramic, metal, metal jacketed ce27. Photo courtesy of Arc Machines Incorporated.
26
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 22—Orbital Weld Head with Wire Feeder
O-RINGS (2)
(3/16 in. [5 mm])
O-RING
(5/16 in. [8 mm])
HIGH IMPACT
CERAMIC NOZZLE
COLLET
COLLET BODY
ELECTRODE
GASKET
SHORT CAP
MEDIUM LONG
TORCH BODY
INSULATOR
GAS LENS HIGH
IMPACT NOZZLE
GAS LENS
COLLET BODY
TORCH BODY
Figure 23—Components of a Typical GTAW Torch, Including Gas Nozzle/Cup,
Gas Lens, Collet Body, Torch Body, Collet, and Electrode
27
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Larger gas nozzles provide better shielding gas coverage,
especially for welding reactive metals such as titanium.
Gas nozzles (cups) are available in a variety of lengths
to accommodate various joint geometries and the required clearance between the gas nozzle and the work.
Longer straight gas nozzles generally produce stiffer, less
turbulent shielding; however, they require longer electrode extensions.
The majority of gas nozzles (cups) are cylindrical in
shape with either straight or tapered ends. To minimize
shielding gas turbulence, nozzles with internal streamlining are available. Nozzles are also available with elongated trailing sections or flared ends which provide
better shielding for welding metals such as titanium,
which is highly susceptible to contamination at elevated
temperatures.
5.5.3.3 Gas Lenses. One device used for assuring a
laminar flow of shielding gas is an attachment called a
gas lens. Gas lenses contain a porous barrier diffuser and
are designed to fit around the electrode or collet. Gas
lenses produce a longer, undisturbed flow of shielding
gas (see Figure 2428) by streamlining the flow of gas as it
exits the torch. They enable operators to weld with the
gas nozzle (cup) 1 in. [25 mm] or more from the work,
improving the welder’s ability to see the weld pool and
allowing them to reach places with limited access such as
inside corners.
Figure 24—GTAW Torch Without a Gas Lens
(Left) and with a Gas Lens (Right)
5.5.4 Cables, Connectors, and Hoses. Gas-cooled
torches usually have a composite power and shielding
gas cable that goes to the torch body. Water-cooled
torches usually have a water inlet hose, a composite
power input and water outlet cable, and a shielding gas
inlet hose.
A protective sheathing over the cable and hoses helps
to reduce abrasive wear. If the extra weight can be tolerated by the welder or in machine applications, the cables
and hoses going to the torch can be wrapped in this protective cover. It is usually easiest to buy this as an assembly from the manufacturer. Nylon braid or glass fiber zip
covers are also available.
carefully prior to installation or use. See Table 3 for typical welding cable capacities. Table 4 provides a guide for
selecting the size of the cable based on the welding current to be used.
Neoprene jacket cables have good resistance to wear
and usually remain flexible over a wide range of operating temperatures. Polyvinyl Chloride (PVC) and other
jacket materials are available but are more susceptible to
damage from heat or abrasive wear.
Stranded copper cables are probably best for the
power return (worklead). In certain applications where
lower RF noise is desired or the most flexibility is required (e.g., a robot) then braided cable may have to be
used. The braided cables are usually larger than stranded
cables for the same current rating.
Another consideration is the inductance of the cable
with respect to the signal going through the cable. In the
use of pulsed arc GTAW the cables should be kept as
short as possible in order to minimize the attenuation and
rounding off of the pulse wave form that occurs because
of the inductance.
5.5.4.1 Cables. Good cables that are large enough
to handle the maximum weld current should be used.
Some cables usually have the current rating and other related information marked on the outside of the jacket at
periodic intervals. Tables 3 and 4 are provided “for reference only” as guides to nominal values for current capacity in a portable welding cable. Actual ratings are
established by the product manufacturer and by
NEMA.29 Actual cable properties should be checked
28. Photo courtesy of CK Worldwide.
29. National Electrical Manufacturers Association.
28
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 3
Typical Welding Cable Capacities
AWG or
MCM Size(1)
Approximate
Net Weight per
100 ft [30.5 m], lb [kg]
Typical OD
Minimum, in. [mm]
Welding Current
Capacity @104°F [40°C]
Ambient, Amperes(2)
Typical Voltage Drop
per 100 ft [30.5 m] @
Maximum Current, Volts
8
6
5
4
10 [4.5].
13 [5.9].
17 [7.7].
20 [9.1].
0.31 [7.9]0
0.37 [9.4]0
0.41 [10.4]
0.43 [10.9]
0 60
0 90
0105
0120
4.00
3.76
3.49
3.17
3
2
1
23 [10]0
29 [13]0
36 [16]0
0.46 [11.7]
0.52 [13.2]
0.57 [14.5]
0180
0240
0300
3.76
3.97
3.95
1/0
2/0
3/0
4/0
43 [20]0
54 [24]0
67 [30]0
83 [38]0
0.63 [16.0]
0.69 [17.5]
0.76 [19.3]
0.83 [21.0]
0360
0450
0540
0640
3.74
3.72
3.54
3.32
250
300
350
400
96 [44]0
115 [52]0
131 [59]0
153 [69]0
0.91 [23.1]
0.96 [24.4]
1.02 [25.9]
1.08 [27.4]
0710
0780
0860
0940
3.12
2.86
2.70
2.59
450
500
600
700
171 [78]0
189 [86]0
226 [103]
260 [118]
1.13 [28.7]
1.18 [29.2]
1.30 [33.0]
1.40 [35.6]
1020
1090
1220
1340
2.50
2.40
2.24
2.10
750
800
900
10000
277 [126]
295 [134]
329 [149]
364 [165]
1.43 [36.3]
1.47 [37.3]
1.53 [38.9]
1.61 [40.9]
1400
1450
1540
1630
2.06
2.00
1.89
1.80
Notes:
(1) The sizes of cable recommended by the Machine Group of the NEMA Electric Welding Section for standard hand-welding equipment based on
total lengths up to 90 ft [27.4 m], that is, 45 ft [13.7 m] of welding cable and 45 ft [13.7 m] of return cable, are as follows:
100 A welding machine—No. 2 cable
200 A welding machine—No. 2 cable
300 A welding machine—No. 1/0 cable
400 A welding machine—No. 2/0 cable
600 A welding machine—No. 3/0 cable
(2) Ampacities are based on a copper temperature of 167°F [75°C] and an ambient temperature of 104°F [40°C] and yield load factors of from approximately 32% for the No. 2 AWG cable to approximately 23% for the No. 3/0 AWG cable and higher for the smaller sizes.
5.5.4.2 Connectors. The termination of the cables
and hoses (usually called connectors) can vary widely
from one manufacturer to another or from one country to
another. This applies to both the torch end and the power
source end connectors for the cable/hoses. This detail
must not be overlooked at the time of purchasing equipment for connections to present equipment or for future
compatibility. There are many adapter fittings available
to connect from one style to another.
make the hose. Gas hoses should be chosen to reduce the
amount of moisture diffusion through the hose wall into
the gas stream. This will help to keep the gas as pure as
possible. A variety of “plastic” gas hoses are becoming
more readily available; all of these usually perform better
than the traditional “rubber” hoses because there is
less permeation of ambient moisture to the gas.31, 32, 33
31. Bhadha, P. 1995. “Control of Moisture and Contaminants in
Shielding Gases.” Welding Journal, Vol. 73, No. 5, pp. 57–63.
32. Bhadha, P. 1999. “How Welding Hose Material Affects
Shielding Gas Quality.” Welding Journal, Vol. 78, No. 7, pp.
35–40.
33. Farish, E. 1994. “Atmospheric Contamination of TIG
Welding Hoses—Causes and Cures,” Welding & Metal Fabrication, Vol. 62, No. 7, pp. 300, 301.
5.5.4.3 Hoses. Gas hoses and water hoses/power
cables may be made from different materials.30 Consideration should be given as to the type of material used to
30. “Practical TIG (GTA) Welding,” Peter W. Muncaster,
1991, Abington Publishing, ISBN 1855730200.
29
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 4
Guide for Selecting the Size of Cable Based on the Welding Current(1),(2)
Distance from Welding Machine, ft [m]
50 [15.2]
75 [22.9] 100 [30.5] 125 [38.1] 150 [45.7] 200 [61.0] 225 [68.6] 250 [76.2] 300 [91.4] 350 [106.7]
Welding
Current, A
100
150
200
250
300
350
400
450
500
550
600
750
900
Cable Size
4
3
2
1
1
1/0
2/0
2/0
3/0
4/0
250 MCM
350 MCM
500 MCM
4
2
1
1/0
2/0
3/0
4/0
4/0
—
—
—
—
—
2
1
1/0
2/0
3/0
4/0
4/0
—
—
—
—
—
—
2
1/0
2/0
3/0
4/0
—
—
—
—
—
—
—
—
1/0
3/0
4/0
—
—
—
—
—
—
—
—
—
—
1
2/0
3/0
4/0
—
—
—
—
—
—
—
—
—
2/0
4/0
—
—
—
—
—
—
—
—
—
—
—
2/0
4/0
—
—
—
—
—
—
—
—
—
—
—
3/0
—
—
—
—
—
—
—
—
—
—
—
4/0
—
—
—
—
—
—
—
—
—
—
—
—
Notes:
(1) Neoprene welding cable, 600 volt, Class K (30 AWG), flexible stranding copper. Figures above represent half the length needed for a welding
installation based on voltage drop of 4 volts per IPCEA and NEMA specifications. These figures should be doubled to obtain total cable length
(i.e., welding lead plus the work lead length).
(2) Based on information provided by:
(a) Nehring Electrical Works Company, P.O. Box 965, 813 East Locust Street, DeKalb, IL 60115 (Tel. 815-756-2741), and
(b) ExCel Wire and Cable Co., 108 Elm Avenue, P.O. Box D, Tiffin, OH 44883 (Tel. 419-448-0434).
The flexibility of the material at various temperatures
also must be considered. (See Section 7 for an in-depth
discussion on gas purity.) Composite water hoses and
power cables are usually made from materials that have a
trade off between the dielectric insulation factors and the
resistance to other factors such as corrosion, permeation
of moisture through the hose, and flexibility.
5.6 Wire Feeders. Wire feed systems are made from a
number of components and vary from simple to complex.
The basic system consists of a means of gripping the
wire sufficiently to pull the wire from the spool and push
it through a conduit to a guide tube to the point of welding. Electronic switches and controls are necessary for
the electric drive motor. The wire can be either ambient
temperature (cold) or preheated (hot). (Note: The hot end
of the wire must be maintained in the shielding gas
stream.)
5.5.5 Water Coolers and Re-Circulators. The coolant in water-cooled torches is usually maintained in a
closed system including a reservoir, pump, and radiator
or water chiller to disperse heat from the system. The capacity of these systems ranges from one to fifty gallons.
The coolant is typically propylene glycol/water mixtures
in approximately 50-50 proportions. This helps to prevent freezing, minimizes corrosion and provides lubrication for the water pump. These systems can also be used
for cooling some tooling.
Deionized water is preferred over standard tap water
because of minerals and contaminants in tap water that
can clog the torch. If deionized water is used, the supply
should be changed periodically. Some manufacturers
recommend every three months.
5.6.1 Cold Wire. The system for feeding cold wire
has three components:
(1) A wire drive mechanism that either pushes or
pulls the wire off the wire spool.
(2) A speed control to regulate the speed at which the
wire is delivered into the weld pool.
(3) A wire guide attachment that ensures proper delivery and placement of the wire into the weld pool.
The filler wire is normally fed into the leading edge of
the weld during cold wire welding. Cold wire feeders
usually include controls for wire start delay and automatic retract prior to extinguishing the arc. Cold wire
30
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Figure 26—Schematic of
GTAW with Hot Wire Feed
holder from which inert gas flows to protect the hot wire
from oxidation. The hot wire is generally fed into the
weld pool following the arc. This system is schematically
illustrated in Figure 26.34 Normally, a mixture of 75%
helium and 25% argon is used to shield the tungsten electrode and the molten weld pool. Sometimes the interaction of the electrical current used to heat the wire and the
arc can result in unwanted deflection of the arc or “arc
blow.” In this situation a low voltage AC current is utilized to correct the “arc blow.”
Figure 25—GTAW Torch
with Cold Wire Feed
5.7 Arc and Torch Oscillators. Oscillation can be used
in manual, mechanized, and automatic welding. For
manual welding, the welder moves the torch side to side
or back and forth along the length of weld. In mechanized welding the oscillation is typically produced by
moving the entire welding torch by mechanical means or
by moving the arc plasma with the aid of an externally
applied magnetic field. The control variables in arc oscillation are oscillation speed, displacement direction, end
dwell times, amplitude, and frequency.
feeders can be used in semiautomatic, mechanized, and
automatic GTAW applications. They are available in
2 in.–12 in. [50 mm–300 mm] spool versions. Wires
ranging from 0.015 in.–3/32 in. [0.4 mm–2.4 mm] in
diameter are used. Special wire feeders are available to
provide continuous, pulsed or intermittent wire feed.
Figure 25 shows a GTAW torch with cold wire feed.
Aluminum wire may require other special features built
into the wire feeder.
Oscillation allows placing the welding heat at precise
locations. Figure 27 shows a deep groove weld where
magnetic arc deflection is used to place stringer beads
with limited torch movement. This is advantageous when
welding irregular shaped parts. The number of welding
passes and total heat input can be reduced when arc
5.6.2 Hot Wire. The process for hot wire addition is
similar to that for cold wire, except that the wire is either
resistance or induction heated to a temperature close to
its melting point just before it contacts the molten weld
pool. When using a preheated (hot) wire in machine and
automatic gas tungsten arc welding in the flat position,
the wire is fed mechanically to the weld pool through a
34. AWS Welding Handbook, 8th Edition, Volume 2: Welding
Processes, Chapter 3: Gas Tungsten Arc Welding. Figure 3.6,
p. 83.
31
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
1/2 in.
[13 mm]
(A)
Figure 27—Magnetically Deflected
Arc Laying a Stringer Bead
in a Deep Groove Weld
1/2 in.
[13 mm]
oscillation is used which reduces the cost by as much as
50% as well as reducing the weld shrinkage and upsetting. Figure 28 illustrates the differences in distortion by
using magnetic oscillation.35 Arc oscillation is suited to a
wide range of materials including stainless steel, carbon
manganese steels, and nonferrous alloys. Some high
strength low alloy steels should be welded using the
stringer bead technique to meet weld toughness requirements, for which arc oscillation may be detrimental.
Weld performance testing should be completed prior to
using arc oscillation.
(B)
Figure 28—Cross Sections of Welds Made in
1/2 in. [13 mm] Thick Stainless Steel;
(A) with Magnetic Arc Oscillation, and
(B) without Magnetic Arc Oscillation
5.8 Arc Initiation Equipment. There are several common methods used to initiate the welding arc between the
electrode and the work. These methods are necessary
since an arc cannot be initiated using a standard power
source voltage when the electrode to work distance is at
normal welding arc lengths. Arc initiation requires a
much shorter gap between the electrode and work, higher
voltage, or a means of making the gas conductive. The
following methods are the most commonly used to help
initiate an arc at the beginning of the weld cycle.
5.8.1 High-Frequency Starters. High-frequency
starting can be used with DC or AC power sources for
both manual and automatic applications. High-frequency
generators usually consist of a spark-gap oscillator that
superimposes a high voltage AC output at radio frequencies in series with the welding circuit. The generator output is transferred from the spark-gap circuit to the
electrode leg of the welding circuit by means of an air
35. Hicken, G. K., Stucki, N. D., and Randall, H. W., “Application of Magnetically Controlled Welding Arcs,” Welding
Journal, Vol. 55, No. 4, April 1976, pp. 264–267.
32
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
tance to establish the arc. The advantage of this method
of arc initiation is its simplicity of operation for manual
welding. Depending on the instantaneous short circuit
current capability of the welding power source, the current through the welding electrode upon arc initiation
may cause damage to the weldment or the electrode. This
is corrected by limiting the current upon arc start. The
disadvantage of touch starting is the tendency for the
electrode to stick to the workpiece, causing electrode
contamination and transfer of tungsten to the workpiece.
AIR CORE
TRANSFORMER
ELECTRODE
SPARK GAP
OSCILLATOR
WELDING
POWER
SUPPLY
GAS
NOZZLE
HIGH FREQUENCY
GENERATOR
5.8.4 Touch And Retract Starters. The touch and retract starters are similar to contact starting in that the tip
of the electrode is lowered to make contact with the
workpiece. However, the controls in this starter do not
allow current to flow until the electrode begins to be
withdrawn, thus striking the arc. This eliminates the tendency for electrode contamination. Another variation involves a low current to be passed through the electrode,
which heats the electrode tip and allows the arc to more
easily be initiated upon retraction.
WORKPIECE
Figure 29—High-Frequency Arc Starting
core transformer, as illustrated in Figure 29.36 The highfrequency generator produces a series of closely spaced
bursts of high voltage energy. This high voltage ionizes
the gas between the electrode and the work. The ionized
gas will then conduct welding current that initiates the
welding arc.
6. Tungsten Electrodes
6.1 General. In GTAW the word “tungsten” refers to the
pure element tungsten and its various composites used as
welding electrodes. Tungsten electrodes are called “nonconsumable” (if the process is properly used), because
they do not melt or transfer to the weld as a filler metal.
In other welding processes, such as SMAW, GMAW, and
SAW, the electrode is the filler metal. The function of a
tungsten electrode is to serve as one of the electrical terminals in the welding circuit. An electric arc is formed at
the electrode tip and this arc supplies the heat required
for welding.
Pure tungsten has a melting point of 6170°F [3410°C]
and a boiling point of 10220°F [5660°C]37; the melting
and boiling points of tungsten electrodes vary with the
dopant composition. Approaching the high melting temperature, tungsten becomes increasingly thermionic,
which means that the tungsten can more easily emit or
give off electrons. It reaches this temperature by cathodic
or anodic spot heating and resistance heating. Were it not
for the significant cooling effect of electrons emitting
from its tip, during DCEN (straight polarity) operation,
the heating would cause the tip to melt. Provided the
electrode is used within the current-carrying capacity
range for its specific type, diameter and polarity, it is
virtually impossible to melt and/or vaporize a tungsten
electrode during welding in an inert shielding gas
Because radiation from a high-frequency generator
may disturb radio, electronic, and computer equipment,
the use of this type of arc starting equipment is governed
by regulations of the Federal Communications Commission. The user should follow the instructions of the
manufacturer for the proper installation and use of
high-frequency arc starting equipment.
5.8.2 Pulse/Capacitor Discharge Starters. Application of a high-voltage pulse between the tungsten electrode and the work will ionize the shielding gas and
establish the welding arc. This method is generally used
with DC power sources in machine welding applications.
This technique utilizes capacitors and/or inductors to
store energy. The stored energy is typically discharged in
the form of a high voltage impulse to ionize the gas surrounding the welding electrode, thus initiating the arc. If
the arc start is unsuccessful, the process is repeated.
5.8.3 Contact Starting (Scratch or Touch Start).
With the power source energized, and the shielding gas
flowing from the cup, the torch is lowered toward the
workpiece until the tungsten electrode contacts with the
workpiece. The torch is quickly withdrawn a short dis-
37. CRC Handbook of Chemistry and Physics, 54th Edition,
p. B-35, 1973-74. Robert C. Weast, Editor. CRC Press, Cleveland, OH.
36. AWS Welding Handbook, Eighth Edition, Volume 2: Figure 3.21, p. 93.
33
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 5
Chemical Composition Requirements for Tungsten Electrodes(1)
Weight Percent (wt-%)
AWS
Classification
EWP(5)
EWCe-2(5)
EWLa-1(5)
EWLa-1.5
EWLa-2
EWTh-1(5)
EWTh-2(5)
EWZr-1(5)
EWG(4)
Color
Code(6),(7)
UNS
Number(2)
W Min.
(Difference)(3)
Green
Orange(8)
Black
Gold
Blue
Yellow
Red
Brown
Gray
R07900
R07932
R07941
R07942
R07943
R07911
R07912
R07920
—
99.5
97.3
98.3
97.8
97.3
98.3
97.3
99.1
94.5
CeO2
La2O3
ThO2
ZrO2
—
1.8–2.2
—
—
—
—
—
—
Not
Specified
—
—
0.8–1.2
1.3–1.7
1.8–2.2
—
—
—
Not
Specified
—
—
—
—
—
0.8–1.2
1.7–2.2
—
Not
Specified
—
—
—
—
—
—
—
0.15–0.40
Not
Specified
Other Oxides
or Elements
Total
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
General Note: See AWS A5.12/A5.12M-98, Specification for Tungsten and Tungsten-Alloy Electrodes for Arc Welding and Cutting, Table 1.
Notes:
(1) The electrode shall be analyzed for the specific oxides for which values are shown in this table. If the presence of other elements or oxides is indicated
in the course of the work, the amount of those elements or oxides shall be determined to ensure that their total does not exceed the limit specified
for “Other Oxides or Elements, Total” in the last column of the table.
(2) SAE/ASTM Unified Numbering System for Metals and Alloys.
(3) Tungsten content shall be determined by subtracting the total of all specified oxides and other oxides and elements from 100%.
(4) Classification EWG must contain some compound or element additive and the manufacturer must identify the type and minimal content of the
additive on the packaging.
(5) See AWS A5.12/A5.12M for closely matching grades in ISO 6848.
(6) The actual color may be applied in the form of bands, dots, etc. at any point on the surface of the electrode.
(7) The method of color coding used shall not change the diameter of the electrode beyond the tolerances permitted.
(8) Color varies in ISO 6848, Tungsten Electrodes for Inert Gas Shielded Arc Welding and for Plasma Cutting and Welding.
atmosphere. A number of desirable performance characteristics result from additives to tungsten which lower
the electronic work function.
coniated, Th is for thoriated, Ce is for ceriated, La is for
lanthanated and G stands for general or unspecified
oxide additions. Finally, the numbers40 specify the
nominal alloying composition (in wt-%). For instance,
EWTh-1 is a thoriated tungsten electrode that contains a
nominal 1 wt-% thoria.
6.2 Classifications of Electrodes. Tungsten electrodes
are classified on the basis of their chemical compositions, as summarized in Table 5. Requirements for tungsten electrodes are given in the latest edition of AWS
A5.12, Specification for Tungsten and Tungsten Alloy
Electrodes for Arc Welding and Cutting.38 In the AWS
classification system, E stands for an electrode, which is
used as one terminal of the arc welding circuit.39 The W
stands for the chemical symbol for tungsten (also called
Wolfram). The final letters indicate the alloying element
or oxide additions. P designates a pure tungsten electrode
without intentional alloying elements, while all other
designations are for certain oxide additions. Zr is for zir-
A marking system was developed to provide identification of the various types of electrodes, and each tungsten electrode classification has a color code, as shown in
Table 5. Individual electrodes are marked, typically with
a band (or dot) of the appropriate color, on one end of the
electrode. See the latest revision of AWS A5.12 for more
information.
The doped (alloyed) tungsten electrodes contain oxide
additions, which should be evenly dispersed throughout
the entire length of the electrode. These additions lower
the temperature at which the electrodes emit electrons, to
a temperature below the melting point of the tungsten.
These doped tungsten electrodes are able to handle
38. Additional information can be found in various ISO documents, including ISO6848, Tungsten Electrodes for Inert Gas
Shielded Arc Welding, and for Plasma Cutting and Welding.
39. AWS A3.0, Standard Welding Terms and Definitions,
American Welding Society, Miami, FL.
40. An exception is EWZr-1 which is not 1% ZrO2, but rather
0.15%–0.40%.
34
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 6
Typical Current Ranges For Tungsten Electrodes(1) and Recommended Gas Cup Sizes
Direct Current, A
Electrode Diameter
Gas Cup I.D.
(3)DCEN(3)
(3)DCEP(3)
(DCSP)
(DCRP)
Alternating Current, A
Unbalanced Wave AC(3)
Balanced Wave AC(3)
in.
mm
in.
mm
EWX-X(2)
EWX-X
EWP
EWX-X
EWP
EWX-X
0.010
0.020
0.040
(4)0.060(4)
0.093 (3/32)
0.125 (1/8)
0.156 (5/32)
0.187 (3/16)
0.250 (1/4)
0.30
0.50
1.00
1.60
2.40
3.20
4.00
4.80
6.40
1/4
1/4
3/8
3/8
1/2
1/2
1/2
5/8
3/4
6
6
10
10
13
13
13
16
19
Up to 15
5–20
15–80
70–150
150–250
250–400
400–500
500–750
750–1000
N/A
N/A
N/A
10–20
15–30
25–40
40–55
55–80
80–125
Up to 15
5–15
10–60
50–100
100–160
150–200
200–275
250–350
325–450
Up to 15
5–20
15–80
70–150
140–235
225–325
300–400
400–500
500–630
Up to 15
10–20
20–30
30–80
60–130
100–180
160–240
190–300
250–400
Up to 15
5–20
20–60
60–120
100–180
160–250
200–320
290–390
340–525
Notes:
(1) All values are based on the use of argon as a shielding gas. Other current values may be employed depending on the shielding gas, type of equipment,
and application.
(2) EWX-X refers to the X-X dopant and percentage of dopant in the tungsten electrode. See the latest AWS A5.12. Ce-2, La-1, La-1.5, La-2, Th-1,
Th-2, Zr-1 and others may be included in this category.
(3) DCEN = Direct current electrode negative (straight polarity); DCEP = Direct current electrode positive (reverse polarity); AC = Alternating current.
(4) Although the metric size 1.6 mm (0.063 in.) is closer to 1/16 in. (0.0625 in.), it has been common industry practice to refer to the U.S. customary
size 0.060 in. as 1/16 in.
higher welding currents,41 and they typically provide improved arc starting characteristics, help stabilize the arc,
and increase the life of the electrodes. However, each has
distinct electrical and arc characteristics, which may result in different welding performances and weld bead
shapes.
The pure tungsten electrodes are more prone to contamination of the weld than the other types of tungsten
electrodes. They are generally only used for AC welding,
because DC welding with pure tungsten electrodes typically produces small amounts of tungsten inclusions (discontinuities) in the weld.
6.2.1 Pure Tungsten Electrodes (EWP). Pure tungsten electrodes (EWP) contain a minimum of 99.5%
tungsten, with no intentional alloying elements, as summarized in Table 5. The current-carrying capacity of pure
tungsten electrodes is lower than that of the doped (alloyed) tungsten electrodes (see Table 6). Pure tungsten
electrodes are used mainly with AC for welding aluminum and magnesium alloys. The tip of the EWP electrode maintains a clean, balled end (see Figure 3042),
which provides good arc stability. The pure tungsten
electrodes also may be used with DC but they do not provide the arc initiation and arc stability characteristics of
thoriated, ceriated, or lanthanated electrodes. DCEP (reverse polarity) welding causes splitting and melting of
pure tungsten electrodes.
6.2.2 Zirconiated Tungsten Electrodes (EWZr-1).
Zirconiated tungsten electrodes (EWZr-1) contain a
small amount of zirconium oxide (ZrO2, referred to as
zirconia), as listed in Table 5. Zirconiated tungsten electrodes have welding characteristics that generally fall between those of pure tungsten and thoriated tungsten.
They are normally the electrode of choice for AC welding of aluminum and magnesium alloys because they
combine the balled end typical of pure tungsten along
with the higher current capacity (see Table 6), desirable
arc stability and better arc starting characteristics of thoriated tungsten electrodes. They are more resistant to
tungsten contamination of the weld pool than pure tungsten and are preferred for radiographic-quality aluminum
welding applications where tungsten contamination of
the weld must be minimized.
41. Ushio, M. and Matsuda, F., 1986, “Study on Gas-TungstenArc Electrodes: Comparative Study on Characteristics of
Tungsten-Oxide Cathode.” IIW Doc. #212-648-86.
42. Photo courtesy of Pratt & Whitney.
6.2.3 Thoriated Tungsten Electrodes (EWTh-X).
Thorium oxide (ThO2, called thoria) is the present industrystandard additive to tungsten electrodes. Two types of
35
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
The EWTh-1 and EWTh-2 tungsten electrodes were
designed for DCEN applications. They maintain a sharpened tip configuration during welding, which is desirable
for the welding of steel, nickel alloys, and most alloys
other than aluminum or magnesium. Thoriated tungsten
electrodes are not normally used with AC welding because it is difficult to maintain the balled end, which is desirable with AC welding, without splitting the electrode.
EWTh-3 is a discontinued classification of tungsten
electrode, which had a blue color code. Note: the new
EWLa-2 now uses a blue color code. This tungsten electrode had an integral longitudinal or axial segment
throughout its length which contained 1.0 wt-%–2.0 wt% thoria and the average thoria content of the electrode
was 0.35 wt-%–0.55 wt-%. Advances in powder metallurgy and other processing developments have caused
this electrode classification to be discontinued, as it has
limited commercial applicability.
SAFETY NOTE*
Thoria is a very low-level radioactive oxide. However, if welding is to be performed in confined spaces
for prolonged periods of time or if electrode grinding
dust might be ingested, special precautions relative to
ventilation should be considered. The user should
consult appropriate safety personnel.
The level of contamination/radiation has not been
found to represent a health hazard during welding, but
rather the grinding dust from the electrodes may be a
concern.43, 44, 45, 46 However, in other nations, especially
European countries, tungsten electrodes containing
greater than 2% thoria are used less now because of
concerns with radiation exposure to the welder. Alternative rare earth doped tungsten electrodes are available
and are discussed below.
Figure 30—Balled Tip on the End of a Pure
Tungsten Electrode Used for AC Welding
thoriated tungsten electrodes are readily available, as
shown in Table 5. The EWTh-1 electrodes contain a
nominal 1% thoria and the EWTh-2 electrodes contain a
nominal 2% thoria, evenly dispersed through their entire
lengths.
6.2.4 Ceriated Tungsten Electrodes (EWCe-2). The
EWCe-2 electrodes are tungsten alloy electrodes
Thoriated tungsten electrodes are superior to pure
tungsten electrodes in several respects. The thoria is responsible for increasing the usable life of these electrodes compared with the pure tungsten electrodes. This
is because the thoria provides higher electron emissivity,
typically 20% higher current carrying capacity (see Table
6), generally longer life, lower electrode tip temperatures, and greater resistance to contamination of the
weld. With these electrodes, arc starting is easier, and the
arc is more stable than with pure tungsten or zirconiated
tungsten electrodes for DC welding.
43. “Thoriated Tungsten Electrodes Studied for Effects on Welders’
Health,” Welding Journal, Vol. 73, No. 5, May 1994, pp. 88–89.
44. Vinzents, P., Poulsen, O. M., et al., 1994. “Cancer Risk and
Thoriated Welding Electrodes,” Occupational Hygiene, Vol. 1,
no. 1, 1994 pp. 27–33.
45. McElearny, N. and Irvine, D., 1993. “A Study of Thorium
Exposure During Tungsten Inert Gas (TIG) Welding in an Airline Engineering Population,” Journal of Occupational Medicine, Vol. 35, No. 7, July 1993, pp. 707–711.
46. British Health and Safety Executive Information Document
HSE 564/56, June 1991.
*ANSI/AWS A5.12/A5.12M-98, Specification for Tungsten and
Tungsten-Alloy Electrodes for Arc Welding and Cutting, p. 8.
36
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
containing a nominal 2% cerium oxide (CeO2—referred
to as ceria), as shown in Table 5. These electrodes were
developed as possible replacements for thoriated tungsten electrodes because ceria, unlike thoria, is not a
radioactive material. Compared with pure tungsten, the
ceriated tungsten electrodes provide similar current levels (Table 6) and the improved arc starting and arc stability characteristics of thoriated tungsten electrodes.
EWCe-2 electrodes are recommended for DCEN welding but can operate successfully with AC.
Because these electrodes contain a different oxide
than the thoriated tungsten electrodes, the electrical characteristics are slightly different. The ceriated tungsten
electrodes operate at slightly different arc voltages/arc
lengths than the thoriated tungsten electrodes. For mechanized and automated welding slight changes to the
welding parameters and procedures may be required.
Table 7
Comparison of Surface Finish Designations
Grit
500
320
240
180
120
4–16
10–32
15–63
70–90
100
0.1–0.4
0.2–0.8
0.4–1.6
1.8–2.3
2.5
Ra (Pin.)
Ra (Pm)
3.6–14.4
9.0–28.8
13.5–56.8
63.1–81.1
90
0.1–0.4
0.2–0.7
0.3–1.4
1.6–2.1
2.3
Note:
(1) RMS (Pin.) = 1.1 Ra (Pin.).
6.3 Surface Finishes. Electrodes with a ground finish
are recommended. Electrodes with a ground finish are
processed to produce a uniform size (usually by centerless grinding which is done to remove surface imperfections). They are then chemically cleaned to remove any
surface impurities. The ground-finish electrodes typically provide better electrical current conduction from
the collet to the electrode and behave more predictably
and more uniformly over time and from electrode to
electrode. The ground-finish electrodes are supplied with
a bright, polished surface with a maximum surface
roughness of 32 μin. AARH [0.8 μm Ra]. See Table 7 for
a comparison of surface finishes. Clean-finished electrodes (produced by chemically cleaning the surface to
remove only surface impurities after the forming operation) are no longer part of AWS A5.12. Electrodes with
a clean (only) finish may be available but are not
recommended.
6.2.5 Lanthanated Tungsten Electrodes (EWLa-X).
The EWLa-X categories of tungsten electrodes were developed as nonradioactive alternatives to thoria. These
electrodes contain lanthanum oxide (La2O3, referred to
as lanthana) in various contents from 1 wt-% to 2 wt-%,
as shown in Table 5. The electrodes with higher concentrations of dopants provide greater electron emission efficiencies. The current levels (see Table 6), advantages,
and operating characteristics of these electrodes are very
similar to the ceriated tungsten electrodes (although
these electrodes operate at slightly different arc voltages
than thoriated or ceriated tungsten electrodes).
6.2.6 Other Tungsten Electrodes (EWG). The EWG
electrode classification was assigned for electrode compositions not included in the above classes. These electrodes contain an unspecified addition of some oxide or
combination of oxides (rare earth or others). The purpose
of the addition is to improve the nature or characteristics
of the arc, or the life of the electrode.
Several EWG electrodes are either commercially
available or are being developed. These include additions
of yttrium oxide or magnesium oxide, or ceriated and
lanthanated tungsten electrodes that contain these oxides
in amounts other than as listed in Table 5 or in combination with each other or with other oxides. AWS A5.12 requires that the specific type and nominal content of the
alloy (dopant) addition shall be marked on the packages.
Potential increase in electrode life and improved operating characteristics may result from oxide additions of
several rare earths in combination.47
6.4 Electrode Sizes and Current Capacities. Tungsten
electrodes are available in a variety of standard diameters
(sizes), as listed in Table 6. These tungsten electrodes are
commercially available in standard lengths of 2, 3, 6, 7,
12, 18, and 24 in. [50, 75, 150, 175, 305, 455, and 610
mm48] with blunt ends (i.e., no end preparation). Shorter
electrodes for applications such as orbital welding equipment are usually available from the equipment manufacturers or other suppliers. Lengths from 1/4 in.–2 in.
[6 mm–50 mm] are typically used and can be purchased
cut to exact lengths and pre-ground with exact tip configurations (see Figure 3149).
The choices of an electrode classification, size, and
welding current are influenced by the type and thickness
47. Ushio, M., Matsuda, F. and Sadek, A. A. 1992. “GTA
Welding Electrodes,” International Conference on Trends in
Welding Science and Technology, June 1992, p. 405–409;
ASM Conference Proceedings. Edited by S. A. David and J. M.
Vitek.
48. Standard sizes and lengths in ISO6848 “Tungsten electrodes for inert gas shielded arc welding, and for plasma cutting
and welding,” although tolerances differ in some cases.
49. Figure 2, Welding Journal, Vol. 74, No. 1, Jan. 1995, p. 41.
37
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
RMS(1) (Pin.) RMS (Pm)
Not for Resale
AWS C5.5/C5.5M:2003
ing. For DCEN welding, tapering of the electrode tip is
usually done for all but the smallest electrodes.
Various electrode tip geometries affect the weld bead
shape and size. In general, as the included angle increases, weld penetration increases and the width of the
weld bead decreases (see Figure 1450). Electrode tip configuration is a welding variable that should be studied
during welding procedure development and adhered to
during production, especially for mechanized and automated welding.
Regardless of the electrode tip geometry selected, it is
important that a consistent tip configuration be used once
a welding procedure is established. Changes in electrode
geometry can have a significant influence not only on the
weld bead width, depth of penetration, and resultant
quality, but also on the electrical characteristics of the arc
(e.g., arc voltage), arc stability, and electrode life. If the
electrode geometry is not selected correctly, tungsten inclusions may result.
THE ELECTRODES ARE PRECUT
TO LENGTHS FOR AUTOMATIC
ORBITAL WELDING MACHINES.
THE ELECTRODES SHOWN
HAVE NOT BEEN TRUNCATED.
Figure 31—Ground Tapered Tip on End
of Doped Tungsten Electrodes
6.5.1 Balling. With AC welding, a hemispherical tip,
or “ball,” is most desirable. Before use in welding, the
electrode tip is balled by striking an arc on a copper
block or other suitable material using AC or DCEP. Arc
current is increased until the end of the electrode turns
white hot and the tungsten begins to melt, causing a
small ball to form at the end of the electrode, as illustrated in Figure 30. The current is downsloped (decreased gradually) and extinguished, leaving a
hemispherical ball on the end of the tungsten electrode
(shielding gas flow must be maintained while the tip is
cooling). The size of the hemisphere should be between
1 and 1-1/2 times the electrode diameter.
of base metals being welded, as listed in Table 8. The
current carrying capacities of all types of tungsten electrodes are affected by the type of welding torch, the type
of power source (DCEN, DCEP, AC, or variable polarity), the electrode extension beyond the collet, and the
shielding gas. Tables 6 and 9 list suggested current
ranges for each electrode type and size using argon
shielding gas, along with gas cup diameters recommended for use with different types of welding power.
Since the maximum current capacity of an electrode depends on many factors (see 4.4.1.2 and 4.4.1.3), the typical current ranges should be used only as a guide. In
general, all of the electrodes may be used with argon or
helium, or with a combination of these shielding gases.
6.5.2 Grinding. The most common method of preparing the tip is by grinding. Figure 33 illustrates typical
grinding, cutting, and truncating methods in preparing
tungsten electrodes for DCEN welding.
To produce optimum arc stability, grinding of thoriated, ceriated, and lanthanated tungsten electrodes
should be done with the axis of the electrode perpendicular to the axis of the grinding wheel and ground on the
flat face of the wheel (i.e., the electrode should be
ground in the longitudinal direction) as shown in Figure
33.51 A polished surface condition of better than 10 μin.
RMS [0.2 μm] will help to extend the electrode life. Circumferential grinding of the electrode tip is not recommended because it can result in arc instability if the
6.5 Electrode Tip Configurations. The shape of the
tungsten electrode tip is an important process variable in
GTAW. Tungsten electrodes may be used with a variety
of tip preparations. With AC welding, pure or zirconiated
tungsten electrodes form a hemispherical balled end (see
Figure 30). Thoriated, ceriated and lanthanated tungsten
electrodes do not ball as readily as pure or zirconiated
tungsten electrodes, and are typically used for DC welding. For these, the end is typically beveled to a conical
shape with a specific included angle, usually with a truncated end (see Figure 32). A small flat at the tip of the
electrode is important to avoid the tip breaking off. These
doped electrodes maintain a ground tip shape much better than the pure tungsten electrodes. Table 9 is a guide
for electrode tip preparation for a range of sizes with recommended current ranges.
50. J. F. Key, “Anode/Cathode Geometry and Shielding Gas
Interrelationships in GTAW,” Welding Journal, Vol. 59, No. 12,
Dec. 1980, p. 365-s.
51. “A Guide to Tungsten Electrode Geometry and Preparation,” Practical Welding Today, Vol. 2, No. 2, March/April
1998.
Tungsten electrode tip configurations are prepared by
balling or grinding. For AC welding the square end of the
electrode is sometimes slightly chamfered prior to ball-
38
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 8
Recommended Types of Current, Tungsten Electrodes,
and Shielding Gases for Welding of Various Metals and Alloys
Thickness
Type of Current(1),(2)
Electrode(3)
Shielding Gas
Aluminum
All
> 1/8 in. [3 mm]
d 1/8 in. (3 mm)
AC
DCEN
DCEP
Pure or zirconiated
Thoriated
Thoriated or zirconiated
Argon or argon-helium
Argon-helium or argon
Argon
Copper, copper alloys
All
< 1/8 in. [3 mm]
DCEN
AC
Thoriated
Pure or zirconiated
Helium or argon-helium
Argon
Magnesium alloys
All
< 1/8 in. [3 mm]
AC
DCEP
Pure or zirconiated
Zirconiated or thoriated
Argon
Argon
All
DCEN
Thoriated
Argon
Plain carbon, low-alloy steels
All
< 1/8 in. [3 mm]
DCEN
AC
Pure or zirconiated
Thoriated
Argon or argon-helium
Argon
Stainless steel
All
< 1/8 in. [3 mm]
DCEN
AC
Thoriated
Pure or zirconiated
Argon or argon-helium
Argon
All
DCEN
Thoriated
Argon
Type of Alloy
Nickel, nickel alloys
Titanium
Notes:
(1) Where AC is listed, variable polarity or pulsed current could be used.
(2) AC = Alternating current; DCEP = Direct current electrode positive; DCEN = Direct current electrode negative.
(3) Where thoriated electrodes are recommended, ceriated or lanthanated electrodes may also be used.
Table 9
Tungsten Electrode Tip Shapes and Examples of Current Ranges
DCEN (Electrode Negative/Straight Polarity)(1),(2)
Electrode Diameter
Diameter at Tip
in.
mm
in.
mm
Included
Angle,
Degrees
0.040
0.040
0.060
0.060
0.093
0.093
0.125
0.125
1.00
1.00
1.60
1.60
2.40
2.40
3.20
3.20
0.005
0.010
0.020
0.030
0.030
0.045
0.045
0.060
0.125
0.250
0.50
0.80
0.80
1.10
1.10
1.50
12
20
25
30
35
45
60
90
Constant
Current
Range, A
Pulsed
Current
Range, A
2–15
5–30
8–50
10–70
12–90
15–150
20–200
25–250
2–25
5–60
8–100
10–140
12–180
15–250
20–300
25–350
Notes:
(1) All values are based on the use of argon as the shielding gas. Other current values may be used, depending upon the shielding gas, type of equipment
and application.
(2) These values will vary depending on duty cycle, pulse frequency, peak/background ranges, etc.
Figure 32—Ground Electrode Tip Geometry
39
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 33—Typical Preparation Method of Tungsten Electrodes Used for
GTA Welding, Including Tip Truncation, Grinding, and Cutting
40
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
surface finish is not smooth enough. The desired surface
finish of a ground electrode is illustrated in Figure 34.52
The grinding wheel should be reserved for the grinding of only tungsten to eliminate possible contamination
of the tungsten tip with foreign matter during the grinding operation. Grinding on diamond wheels is preferred
over silicon carbide or aluminum oxide wheels. Equipment designed specifically for grinding and cutting tungsten electrodes is available. Exhaust hoods and personal
protective equipment (PPE) should be used when grinding tungsten and tungsten alloy electrodes to remove the
grinding dust from the work area.53, 54, 55, 56, 57, 58, 59, 60
POLISHED FINISH:
• Maximum electrode life
• Ideal for high purity welding
• Extremely consistent finish and
angle
• Diamond ground and polished
longitudinally
• Excellent arc starting and
stability
STANDARD FINISH:
• Consistent finish and angle
• Diamond ground in longitudinal
direction
• Good to excellent electrode life
• Exceeds all standards set by
automatic welding equipment
manufacturers
6.6 Electrode Cutting. One of the most overlooked
areas of tungsten electrode preparation is the removal of
the contaminated and/or oxidized tip. A contaminated
electrode produces an erratic arc and a dirty, contaminated weld. Although many welders will simply regrind
contaminated electrodes, the recommended practice is to
cut off the contaminated portion prior to regrinding.
The way to cut tungsten electrodes or remove a
contaminated tip is noted in Figure 35.52 The tungsten
should be rigidly secured on either side of the cut. The
cutting wheel preferably should be diamond to provide a
clean, contamination free, smooth separation. This will
insure the electrode is not fractured or splintered during
the cut off operation. The use of a silicon carbide
type wheel, which contaminates the tungsten, is not
recommended.
Improper methods of removing the electrode tips include breaking with wire cutters, by hand, with a hammer, on a grinding wheel, or other similar means. These
produce splintering or shattering of the electrode tip, and
also create safety concerns.
HAND GROUND FINISH:
• Inconsistent finish
• Incorrectly ground angle
• Poor arc stability and starting
• Reduced electrode life
• Risk of tungsten inclusions and
potential X-ray defect from
tungsten erosion
• Involves potentially hazardous
hand grinding
Figure 34—The Desired Surface Finish
of a Ground Electrode
6.7 Factors Affecting Electrode Life. The life of any
tungsten electrode is shortened by excessive electrode
extension from the collet, excessive welding current, or
electrode contamination, all of which can adversely affect the arc characteristics. The electrode extension beyond the collet should be kept to a minimum to ensure
protection of the electrode by the inert shielding gas. Too
long of an extension can cause overheating and possible
melting or cracking of the electrode.
52. Photo courtesy of Diamond Ground Products.
53. “Thoriated Tungsten Electrodes Studied for Effects on
Welders’ Health,” Welding Journal, Vol. 73, No. 5, May 1994,
pp. 88–89.
54. Vinzents, P., Poulsen, O. M., et al., 1994. “Cancer Risk and
Thoriated Welding Electrodes,” Occupational Hygiene, Vol. 1,
No. 1, 1994, pp. 27–33.
55. McElearny, N. and Irvine, D., 1993. “A Study of Thorium
Exposure During Tungsten Inert Gas (TIG) Welding in an Airline Engineering Population,” Journal of Occupational Medicine, Vol. 35, No. 7, July 1993, pp. 707–711.
56. British Health and Safety Executive Information Document
HSE 564/56, June 1991.
57. MSDS sheets, tungsten mfg.
58. “Practical TIG (GTA) Welding,” Muncaster, P. W., 1991,
pp. 25, Abington Publishing, ISBN 1855730200.
59. Campbell, R. D. and LaCoursiere, E. J., 1995. “A Guide to
the Use of Tungsten Electrodes for GTA Welding.” Welding
Journal, Vol. 74, No. 1, Jan. 1995, pp. 39–45.
60. AWS A5.12/A5.12M-98, Specification for Tungsten and
Tungsten-Alloy Electrodes for Arc Welding and Cutting, p. 8.
6.7.1 Improper Current Levels. Excessively high
current levels for the specific tungsten electrode size can
cause the electrode to quickly erode, melt or split. In
many cases of excessive current, tungsten particles will
be deposited into the weld pool and become a discontinuity in the weld joint. In certain high amperage applications, a cold electrode can exhibit “tungsten spitting” if it
is brought rapidly or instantaneously up to the welding
current. This will usually result in high-density tungsten
inclusions in the weld. This condition can be reduced or
eliminated by starting the arc at a low current and slowly
41
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 35—Proper Cutting of Tungsten Electrodes with a Diamond Cut-Off Blade
6.9 Grinding Dust.61 The grinding (sharpening) of tungsten electrodes generates tungsten metal dust. This dust
may also contain small amounts of oxides like zirconia,
ceria, lanthana and/or thoria. Dust generated by grinding
can be considered a health hazard and most health authorities recommend that all metal grinding machines provide
transparent eye shields, dust extractors and filters. No
dust produced by tungsten grinding should be inhaled by
the person doing the grinding or by adjacent personnel.
Metal dust can cause pulmonary illness over long periods
of inhalation, so it is common sense to protect oneself.
Good shop practice and common sense should be used for
grinding anything. Wear a full-face shield and safety
glasses fitted with side shields, and do not wear loose fitting clothing that could get caught in the machine.
If electrode-grinding dust might be inhaled, special
precautions relative to ventilation should be considered.
A vacuum or exhaust system should be used when grinding electrode tips. Grinding dust from electrodes must not
be inhaled. The user should consult the appropriate safety
procedures, the manufacturer’s suggested procedures,
and follow all company internal safety requirements.
increasing it to the welding current. Current that is too
low for a specific electrode diameter may cause arc wandering and arc starting problems.
6.7.2 Contamination of the Electrode. Metal contamination of the tungsten electrode is most likely to
occur when a welder accidentally dips the tungsten into
the molten weld pool or touches the tungsten with the
filler metal. These often produce tungsten inclusions in
the weld. The tungsten electrode may also become oxidized by use of an improper shielding gas, insufficient
gas flow, loose/leaking gas fittings or gas nozzle (cup),
wind or high air movements, or prematurely shutting off
the shielding gas flow. Other sources of contamination
include: metal vapors from the welding arc, weld pool
eruptions or spatter caused by gas entrapment, and evaporated surface impurities.
6.8 Removing Contamination. When the tungsten electrode becomes contaminated, the welding operation
should be stopped and the contaminated portion of the
electrode removed. The contaminated portion of the electrode should be cut off and then properly redressed to the
appropriate tip configuration (see 6.5.2).
61. See footnotes from 6.5.2.
42
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
6.10 Storage. No firm guidelines have been established
for the storage of thoriated tungsten electrodes by the
American Welding Society62 or the IIW Commission VII.
Guidelines may be incorporated in the Material Safety
Data Sheets (MSDS) provided by the manufacturers.63
Thorium is a naturally occurring radioactive element
that is used in a wide range of industrial processes and
applications. The main hazard is associated with inhalation of dust particles generated during tip grinding.
Thoriated tungsten electrodes, when not in use,
should be stored together in a steel cabinet or similar
metal container. The number of electrodes in storage
should be kept to a minimum, taking into account the expected usage and availability of further stock from the
manufacturer or supplier. As discussed in an earlier section, local exhaust ventilation should be provided at the
grinding operation. The spent tips and grinding dust from
the collection unit should be disposed of in a sealed container to the appropriate location as may be required by
any local, state and federal laws and any company policies. A manager or supervisor should be given the responsibility to ensure that a safe system is in place and
followed.
7.1 Torch Shielding Gas
7.1.1 Purpose of Torch Shielding Gas. The primary
purpose of the torch shielding gas is to protect the electrode, the molten weld metal and the “hot” end of any
filler metal from atmospheric contamination. This contamination is caused mainly by oxygen and water vapor
present in the atmosphere.
Note: Many of the examples in this section are, in detail,
related to the welding of pipe or tubing. The basic principles that these examples are meant to amplify, extend and
apply to all GTAW applications.
7.1.2 Types and Selection of Shielding Gases.
Argon and helium or mixtures of the two are the most
common types of inert gases used for shielding. Argon is
preferred for most applications, except where helium’s
higher heat input is required for welding thick sections of
metals and alloys with high heat conductivity, such as
aluminum and copper. In addition, the lower unit cost
and the lower flow rate requirements of argon make
argon preferable from an economic point of view.
Argon-hydrogen mixtures and sometimes argon-nitrogen mixes are used for special applications. The different
gas mixtures are used to tailor the weld penetration geometry and to improve deposition rates or travel speeds.
Later sections will provide guidelines for using shielding
gas mixtures. Tables 8 and 13 provide a summary of
some common shielding gases and shielding gas mixtures used for gas tungsten arc welding of different base
metals.
7. Gas Shielding, Purging, and
Backing64
Shielding gas is directed through the torch to the arc
and the weld pool to protect the electrode, the filler metal
and the molten weld metal from atmospheric contamination. Backup purge gas can also be used to protect the underside of the weld and its adjacent base metal surfaces
from oxidation during welding. Uniformity of root bead
(underbead) contour, freedom from undercutting, and the
desired amount of root bead reinforcement are more
likely to be achieved when using gas backup under controlled conditions. In some materials, gas backup reduces
root cracking and porosity in the weld. Most alloys when
welded require shielding gas backing; two exceptions
may be aluminum and carbon steel. Some general and
thermodynamic properties of gases are summarized in
Tables 10 and 11 for reference. See Table 12 for dew
point conversions. See 7.6 and 15.7 for additional information on gas safety.
Depending on the volume of usage, these gases may
be supplied in compressed gas cylinders or as a liquid in
insulated tanks. The liquid is vaporized and piped to
points within the plant, thus eliminating cylinder handling. Leaking manifold systems are quite common; thus
care must be taken to keep the system leak tight.
7.1.2.1 Argon (AWS classification SG-A). The
most commonly used shielding gas is argon. Argon is a
heavier-than-air monatomic gas with an atomic weight of
40 and a density of 1.7837 g/L at standard temperature
and pressure (STP).65 Argon is available in various
grades (see 7.3). It is a chemically inert, colorless, odorless, tasteless nontoxic gas. It is obtained from the atmosphere by the separation of liquid air. AWS classification
SG-A is defined as having a minimum purity of 99.997%
in the gaseous state.
62. “Thoriated Tungsten Electrodes Studied for Effects on
Welders’ Health,” 1994, Welding Journal, Vol. 73, No. 5, May
1994, pp. 88-89.
63. Other countries may have specific recommendations; for
example, the British Health and Safety Executive Information
Document HSE 564/6 (June 1991).
64. Further information on this subject is available in AWS
A5.32 and AWS C5.10.
65. Standard conditions for a gas: measured volumes of gases
are generally recalculated to 32°F [0°C] temperature and
760 mm Hg (approximately 1 atm) pressure, which have been
arbitrarily chosen as standard conditions. These conditions are
referred to as standard temperature and pressure or STP.
43
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 10
General Properties of Gases(1),(2)
Description
Argon
Helium
Hydrogen
Nitrogen
Oxygen
Ar
He
H2
N2
O2
Formula
State
Ionization Potential (eV)
Molecular Weight
Compressed Gas Compressed Gas Compressed Gas Compressed Gas Compressed Gas
15.7
39.95
24.5
4.003
15.6
2.02
15.5
28.01
12.5
32.00
Boiling Point, °C
Boiling Point, °F
Boiling Point, K
–185.7
–302.5
87.3
–268.93
–452.08
4.07
–252.87
–423.17
20.13
–195.8
–320.4
77.2
–182.96
–297.33
90.04
Melting Point, °C
Melting Point, °F
Melting Point, K
–189.2
–308.6
83.8
–272.2
–458.0
0.8
–259.14
–434.45
13.86
–209.86
–345.75
63.14
–218.4
–361.1
54.6
Density (gm/liter) @21.1°C
Density (lb/ft3) @70°F
Specific Volume (ft3/lb) @70°F, 1 Atm
Specific Gravity (air = 1) @70°F
Critical Temp, °C
Critical Temp, °F
Critical Temp, K
Critical Pressure (psia)
Critical Pressure (Atm)
Critical Density (lbs/ft3)
0.00165
0.103
9.67
1.380
–122.4
–188.4
150.6
705.4
48.8
33.07
0.00016
0.010
96.06
0.138
–267.95
–450.30
5.05
33.2
2.336
4.32
0.00008
0.005
192.31
0.0695
–240.0
–399.8
33
188.1
13.0
1.93
0.00115
0.072
13.8
0.967
–146.9
–232.4
126.1
0.00133
0.083
12.1
1.105
–118.5
–181.1
154.5
492.9
34.0
19.38
731.4
50.5
27.17
Notes: References:
(1) CRC Handbook of Chemistry and Physics, 54th Edition, 1973–1974. ISBN: 087819-454-1.
(2) Compressed Gas Association, Pamphlet P-9-92.
Table 11
Thermodynamic Properties of Gases(1)
Description
Argon
Helium
Hydrogen
Nitrogen
Oxygen
Heat Capacity
(BTU/lb–Mole °F)
(Cal/gm–°C)
4.97
4.97
4.98
4.98
6.89
6.89
6.90
6.97
7.03
7.03
Thermal Conductivity
(BTU/hr–sq ft–°F/ft)
(Watts/sq meter–°C)
0.0093
0.0530
0.0823
0.4670
0.096
0.545
0.0146
0.0830
0.0142
0.0806
Specific Heat @1 Atm
(J/Kg–K)
(BTU/lb–°F)
521.3
0.1246
5192.0
1.241
1490.0
3.561
1041.0
0.2487
917.0
0.219
1739.9
7.131953
54.8–148.1
27.5
4.178969
1.3–5.0
250.6
5.581833
9.7–31.2
1489.8
7.05041
46.9–124.7
1726.1
7.039904
53.9–148.9
Vapor Pressure(2),(3)
where A =
where B =
Valid Range K
Notes:
(1) References:
(a) CRC Handbook of Chemistry and Physics, 54th Edition, 1973–1974. ISBN: 087819-454-1.
(b) Compressed Gas Association, Pamphlet P-9-92.
(2) Vapor Pressure P in Torr is given by the following:
Log10P = (–0.2185 A/K) + B
where:
K = Kelvin
A = Molar heat of vaporization in cal/gm-mole
(3) Definition of Vapor Pressure: The pressure exerted when a solid or liquid is in equilibrium with its own vapor. The vapor pressure is a function of
the substance and of the temperature.
44
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 12
Dew Point Conversions(2)
Dew Point(1)
°F
Moisture
°C
Dew Point
Moisture
ppm (v/v)
°F
°C
ppm (v/v)
–59
–59
–58
–58
–57
11.4
12.3
13.3
14.3
15.4
–130
–120
–110
–90
–84
–79
0.10
0.25
0.63
–75
–74
–73
–72
–71
–105
–104
–103
–102
–101
–76
–76
–75
–74
–74
1.00
1.08
1.18
1.29
1.40
–70
–69
–68
–67
–66
–57
–56
–56
–55
–54
16.6
17.9
19.2
20.6
22.1
–100
–99
–98
–97
–96
–73
–73
–72
–72
–71
1.53
1.66
1.81
1.96
2.15
–65
–64
–63
–62
–61
–54
–53
–53
–52
–52
23.6
25.6
27.5
29.4
31.7
–95
–94
–93
–92
–91
–71
–70
–69
–69
–68
2.35
2.54
2.76
3.00
3.28
–60
–59
–58
–57
–56
–51
–51
–50
–49
–49
34.0
36.5
39.0
41.8
44.6
–90
–89
–88
–87
–86
–68
–67
–67
–66
–66
3.53
3.84
4.15
4.50
4.78
–55
–54
–53
–52
–51
–48
–48
–47
–47
–46
48.0
51.0
55.0
59.0
62.0
–85
–84
–83
–82
–81
–65
–64
–64
–63
–63
5.30
5.70
6.20
6.60
7.20
–50
–49
–48
–47
–46
–46
–45
–44
–44
–43
67.0
72.0
76.0
82.0
87.0
–80
–79
–78
–77
–76
–62
–62
–61
–61
–60
7.80
8.40
9.10
9.80
10.5
–45
–44
–43
–42
–41
–43
–42
–42
–41
–41
92.0
98.0
105.0.0
113.0.0
119.0.0
Notes:
(1) Dew Point: The temperature at which, in a given mixture of gas and water vapor, the water vapor will condense out of the gas.
(2) Conversion of ppm to %:
1 ppm = 0.0001%
10 ppm = 0.001%
100 ppm = 0.01%
1000 ppm = 0.1%
45
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 13
Advantages of Shielding Gases
Metal
Welding Type
Shielding Gas
Manual
Argon
Aluminum and
Magnesium
Machine
Carbon Steel
Stainless Steel
Better arc starting, cleaning action and weld quality; lower gas
consumption.
Argon-helium
High welding speeds possible.
Argon-helium
Better weld quality, lower gas flow than required with straight helium.
Helium
(DCSP)
Deeper penetration and higher weld speeds than can be obtained with
argon-helium.
Spot
Argon
Generally preferred for longer electrode life. Better weld nugget
contour, ease-of-starting, and lower gas flows than helium.
Manual
Argon
Better pool control; especially for position welding.
Machine
Helium
Higher speeds obtained than with argon.
Manual
Argon
Excellent control of penetration on light gage materials.
Argon-helium
Machine
Argon-hydrogen
(up to 35%-H2)
Argon-helium
Copper, Nickel, and
Cu-Ni Alloys
Advantages
Higher heat input, higher welding speeds possible on heavier gages.
Prevents undercutting, produces desirable weld contour at low current
levels, requires lower gas flows.
An excellent selection for high speed tube mill operation.
Helium
Provides highest heat input and deepest penetration.
Argon
Ease of obtaining pool control, penetration, and bead contour on thin
gage metal.
Argon-helium
Higher heat input to offset high heat conductivity of heavier gages.
Helium
Highest heat input for welding speed on heavy metal sections.
Argon
Low gas flow rate minimizes turbulence and air contamination of
weld; improved heat-affected zone.
Helium
Better penetration for manual welding of thick sections (inert gas
backing required to shield back of weld against contamination).
Silicon Bronze
Argon
Reduces cracking of this “hot short” metal.
Aluminum Bronze
Argon
Less penetration of base metal.
Titanium
Although argon itself is chemically inert it is readily
ionized to form a plasma. Impurities such as moisture
and oxygen can cause variable arc behavior, and in
the case of sensitive materials such as the reactive
and refractory metals, a reduction in weld metal properties. Oxygen, even at relatively low levels of 50 ppm or
lower, can also cause the oxidation of the tungsten
electrode.
Argon is used more extensively than helium because
of the following advantages:
(1) Smoother, quieter arc action
(2) Reduced penetration (e.g., for thin materials)
(3) Cleaning action when welding materials such as
aluminum and magnesium with AC or DCEP current
(4) Lower cost and greater availability
(5) Lower flow rates for good shielding
(6) Better cross-draft resistance (i.e., denser)
(7) Easier arc starting
(8) Better control of the weld pool
The bead profile of an argon-shielded weld is particularly helpful when manual welding thin material because
the tendency for excessive melt-through is lessened (see
46
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
VERTEX ANGLE
(TRUNCATION,
[mm])
AWS C5.5/C5.5M:2003
GAS MIXTURE
100 Ar
75 Ar–25 He
50 Ar–50 He
25 Ar–75 He
100 He
95 Ar–5 H2
39° [0.125]
60° [0.125]
90° [0.500]
180°
Figure 36—GTA Weld Bead Shape as a Function of Shielding Gas Composition
and Electrode Tip Geometry (on 304 Stainless Steel)
Figure 36 66 for an example of the penetration characteristics). The weld profile characteristic is advantageous in
vertical or overhead welding since the tendency for the
base metal to sag or run is decreased.
Argon is used for welding a wide range of materials,
including mild steel, aluminum, copper, stainless steel,
nickel alloys and the reactive metals, titanium and
magnesium.
lium is a “mined” resource obtained by the separation of
natural gas.
The higher ionization potential of helium, approximately 25eV compared to 16eV for argon, produces a
significantly higher arc voltage at the same arc length
and therefore a hotter arc. For given values of welding
current and arc length, helium transfers more heat into
the work than argon. Because helium has a higher thermal conductivity, it can often promote higher welding
speeds and improve the weld bead penetration.
The greater heating power of the helium arc can be
advantageous for joining metals of high thermal conductivity and for high-speed mechanized applications. Also,
helium is used more often than argon for welding heavy
plate. Mixtures of argon and helium are useful when
some balance between the characteristics of both is desired (see Figure 36 for an example of weld penetration
characteristic).
Although helium offers definite advantages for some
applications, it produces a less stable arc and less desirable arc starting characteristics than argon. As little as
5% argon in helium dramatically increases the ability to
7.1.2.2 Helium (AWS classification SG-He). Helium is the lightest monatomic gas, approximately ten
times lighter than argon with an atomic weight of four
(4). The density of helium is 0.166 g/L at room temperature. Its cost is significantly higher than that of argon.
AWS classification SG-He is defined as having a minimum purity of 99.995% in the gaseous state. A high purity grade of 99.998% is readily available. Helium is a
chemically inert, colorless, odorless, tasteless gas. He66. J. F. Key, 1980, “Anode/Cathode Geometry and Shielding
Gas Interrelationships in GTAW,” Welding Journal, Vol. 59,
No. 12, Dec. 1980, Figure 3, p. 366-s.
47
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
initiate the arc. Helium usually requires higher shielding
flow rates (typically 2 to 3 times greater) than argon because helium is lighter than argon. Helium is more
expensive and is usually provided in high-pressure cylinders that tend to contain more impurities (e.g., oxygen
and moisture) than argon.
ARC VOLTAGE, V
7.1.2.3 Argon–Helium Mixtures (AWS classifications SG-AHe and HeA). Helium is added to argon to
take advantage of the best operating characteristics of
each gas. The superior arc starting and stable arc characteristics of argon, with helium’s higher thermal conductivity, produce high quality GTAW welding of aluminum
using AC. Increased travel speeds and depth of fusion,
for both manual and mechanized welding, can be expected as helium content increases (see Figure 36). Helium content usually ranges between 25% and 75%.
The chief factor influencing shielding effectiveness is
the gas density. Argon is approximately one and onethird times as heavy as air and ten times heavier than helium. Argon, after leaving the torch gas nozzle (cup),
forms a blanket over the weld area.
Helium, because it is lighter, tends to rise around the
gas nozzle (cup). Experimental work has consistently
shown that to produce equivalent shielding effectiveness,
the flow volume67 of helium must be two to three times
that of argon. The same general relationship is true for
mixtures of argon and helium, particularly those high in
helium content.
The important characteristics of these gases are the
voltage-current relationships of the tungsten arc in argon
and in helium that are illustrated in Figure 37.68 At all
current levels, for equivalent arc lengths, the arc voltage
obtained with helium is appreciably higher than that with
argon. Since heat in the arc is roughly measured by the
product of current and voltage (arc power), helium offers
more available heat than argon. The higher available heat
favors its selection when welding thick materials and
25
20
HELIUM
15
ARGON
10
0
0
50
100
150
200
250
300
350
400
ARC CURRENT, A
Figure 37—GTA Voltage—Current
Relationships with Argon and Helium
Shielding Gases for Different Arc Lengths
metals having high thermal conductivity or relatively
high melting temperatures.
However, it should be noted that at lower currents, the
volt-current curves pass through a minimum voltage,
after which the voltage increases as the current decreases. For helium, this increase in voltage occurs in the
range of 50 A–150 A where much of the welding of thin
materials is done. Since the voltage increase for argon
occurs below 50 A, the use of argon in the 50 A–150 A
range provides the operator with more latitude in arc
length to control the welding operation.
It is apparent that to obtain equal arc power, appreciably higher current must be used with argon than with
helium. Since undercutting with either gas will occur at
about equal current levels, helium will produce satisfactory welds at much higher speeds.
Another influential characteristic is arc stability. Both
gases provide excellent stability with direct current
power. With alternating current power, which is used extensively for welding aluminum and magnesium, argon
yields much better arc stability and the highly desirable
cleaning action, which makes argon superior to helium in
this respect.
67. Weight Percent. This is the percentage composition by
weight. This is contrasted with atomic percent, which is the
number of atoms of an element in a total of 100 representative
atoms of a substance.
Volume Percent. This is the fraction of the volume of one
substance with respect to the total volume of all the constituents
(then multiplied by 100). Weight percent gives the absolute
quantity of one substance with respect to the total, whereas
volume percent gives the relative amount of one substance versus the others where the density of each of the constituents vary
individually with conditions of temperature and pressure. This
is why, for comparison, gases are usually normalized referring
to conditions of Standard Pressure and Temperature (STP).
Notwithstanding, volume percent is most practical for metering
gas flow.
68. Reference: AWS Welding Handbook, Eighth Edition, Volume 2: Figure 3.15, p. 89.
7.1.2.4 Argon-Hydrogen Mixtures (AWS classifications SG-AH).69 Hydrogen is the lightest and most
abundant of all the elements in the universe. It is a flammable, colorless, odorless, nontoxic gas. Hydrogen’s gas
69. See AWS A5.32, Specifications for Welding Shielding
Gases, Section A8, General Safety Considerations, and A9,
Safety References.
48
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
ARC LENGTH
0.08 in. [2 mm]
0.16 in. [4 mm]
TUNGSTEN ARC,
ALUMINUM
30
Not for Resale
AWS C5.5/C5.5M:2003
density is 0.08988 g/L at STP. As with the other gases
used for GTAW, several grades are available.
Argon-hydrogen mixtures are employed in special
cases, such as mechanized welding of light gage stainless
steel and nickel based alloys, where the hydrogen does
not cause adverse metallurgical effects such as porosity
and hydrogen-induced cracking. Excessive hydrogen
can cause porosity. Increased welding speeds can be
achieved in almost direct proportion to the amount of hydrogen added to argon because of the increased arc voltage and thermal conductivity. However, the amount of
hydrogen that can be added varies with the metal thickness and type of joint for each particular application.
Hydrogen can be added to argon or helium to increase
the temperature of the arc and to provide a slightly reducing atmosphere. Argon-hydrogen mixtures are typically
1%–7% hydrogen in argon, although higher hydrogen
concentrations have been used. Up to 10% hydrogen addition to either argon or nitrogen is common.
Hydrogen is most commonly used for welding in
combination with argon or nitrogen to improve the wetting characteristics of the weld root by reducing the surface tension of the weld metal. In high-speed tube
welding this helps to reduce the undercut. Mixtures of
hydrogen and argon and mixtures of nitrogen and argon
have been used on specialty tube mill applications.
The higher heat input is derived from the dissociation
of the hydrogen in the arc to form atomic hydrogen,
which then recombines to the molecular form in the
cooler regions of the arc and at the workpiece surface releasing energy to the weld pool. The arc voltage of a hydrogen mixture is correspondingly higher compared to
pure argon or helium for identical arc length and current
settings. The actual voltage will be determined by the arc
length and the welding current level (as a function of the
power source volt-current [V-I] characteristic).
The arc itself in an argon (or helium)-hydrogen gas
mixture is more constricted which improves the weld
penetration, i.e., it produces a greater depth to width ratio
(see Figure 36) and enables higher welding speeds to be
achieved. Additionally, the slightly reducing atmosphere
produces a cleaner weld bead surface and, in multipass
welds, reduces the risk of oxide/slag build up. Figure 38
shows improved surface cleanliness with the 5% hydrogen mixture.
It should be noted, however, that the use of hydrogen
may cause cracking in carbon and alloy steels, and excessive hydrogen may produce weld metal porosity in ferritic steels, aluminum, copper and in multi-pass welds in
nickel and austenitic stainless steels. Argon-hydrogen
mixtures are normally limited to use on austenitic stainless steel, nickel-copper, and nickel-base alloys.
An argon-hydrogen mixture containing 5% hydrogen
is commonly used for mechanized welding of tight butt
Figure 38—Improved Surface Cleanliness on
Monel Welds Produced with the
5% Hydrogen Mixture in Argon
Shielding Gas with GTAW
joints in austenitic stainless steel up to 0.154 in.
[3.9 mm] thick at speeds comparable to helium (50%
faster than argon). It is also used for welding stainless
steel barrels, and tube-to-tube sheet joints in a variety of
stainless steels and nickel alloys.
WARNING
All hydrogen mixtures are potentially flammable
and explosive. Mixtures above 5% may require
special procedures and equipment.
7.1.2.5 Nitrogen (AWS classification SG-N). Nitrogen is nontoxic and for all practical purposes it can be
considered chemically inert at room temperature. Nitrogen is a colorless, odorless and tasteless gas. The density
is 1.2506 g/L. AWS classification SG-N is defined as
having a minimum purity of 99.9% in the gaseous state.
Much higher arc temperatures are available when using
nitrogen, particularly for automatic welding. Copper, duplex stainless steels and other alloys are sometimes
welded with nitrogen or nitrogen mixtures with either or
both argon and helium. Nitrogen/argon mixtures provide
higher arc stability and easier arc starting. To overcome
arc-starting problems in nitrogen, the arc is sometimes
started in argon and then switched to nitrogen or nitrogen
mixtures. In practice, the tungsten electrodes erode faster
in nitrogen.
49
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Small amounts (1%–5%) of nitrogen are sometimes
mixed with argon and other inert gases to improve welding speeds or penetration. Excessive nitrogen can cause
porosity and change the properties of the weldments.
Therefore, user testing should be performed to assure an
acceptable weld is made when nitrogen mixtures are
applied. The most extensive use of nitrogen has been in
Europe.
Table 14
Typical Argon Flow Rates
Gas Flow Rate Range
Welding of austenitic stainless steels with nitrogencontaining shielding gas may reduce weld ferrite content
and increase susceptibility to hot cracking. This is
because nitrogen enhances formation of austenite. Care
should always be exercised when using nitrogencontaining gases to ensure that detrimental metallurgical
effects do not occur.
Current Range (A)
(SCFH)
[SLPM]
5–50
50–150
150–350
350–450
7–10
10–20
15–25
20–30
3–5
5–10
7–12
9–14
screens to prevent interference by the wind or draft are
preferred to an increase in the flow of the shielding gas.
7.1.3 Selection of Shielding Gas. No set rule governs
the choice of shielding gas for any particular application.
Either argon or helium, or a mixture of argon and helium
may be used successfully for most applications, with the
possible exception of manual welding on extremely thin
material, for which argon is essential. Argon generally
provides an arc that operates more smoothly and quietly,
is handled more easily, and is less penetrating than an arc
shielded by helium. A guide to the selection of gases is
provided in Tables 8 and 13.
Turbulence in the gas flow system can cause instabilities in the welding arc, which can introduce defects into
the weld. Sharp bends, sharp edges and massive volume
changes in the gas supply system may cause turbulence
in the gas flow. A good rule of thumb is that the diameters of the hoses or pipes should provide approximately a
5:1 reduction ratio (to the torch inside diameter) to assure
a laminar (nonturbulent) flow. Simply increasing flow
rates may cause more turbulence.
7.1.4 Shielding Gas Flow Rates. Shielding gas flow
rates are based on the type of gas, gas nozzle (cup) size,
weld pool size, and ambient air movement. In general,
the flow rate increases in proportion to the crosssectional area of the gas nozzle. The gas nozzle diameter
is selected to suit the size of the weld pool and the reactivity of the metal to be welded. The minimum flow rate
is determined by the need for a stiff stream of shielding
gas to overcome the heating effects of the arc and local
cross drafts. With the more commonly used manual
torches, typical shielding gas flow rates are 10 SCFH–
25 SCFH70 [5 SLPM–12 SLPM] for argon and
25 SCFH–45 SCFH [12 SLPM–21 SLPM] for helium.
Excessive flow rates cause turbulence in the gas stream,
which may aspirate atmospheric contamination into the
weld pool. Typical argon flow rates for various current
levels are listed in Table 14. A cross wind or draft of
approximately 5 mph [8 km/hr] and sometimes less can
disrupt the shielding gas coverage. The stiffest, nonturbulent gas streams (with high flow velocities) are obtained by incorporating gas lenses in the nozzle (cup) and
by using argon as the shielding gas. Figure 24 illustrates
similar gas flow rates in torches without a gas lens (left)
and with a gas lens (right). Windbreaks or protective
7.1.5 Lack of Shielding. Discontinuities related to the
loss of inert gas shielding are tungsten inclusions,71 porosity, oxide films and inclusions, incomplete fusion, and
cracking. The extent to which they occur is strongly related to the characteristic of the metal being welded. In
addition, the mechanical properties of titanium, aluminum, nickel, and high-strength alloys can be seriously
impaired with loss of inert gas shielding. Gas shielding
effectiveness can often be evaluated prior to production
welding by making a spot weld and continuing gas flow
until the weld has cooled to a low temperature. A bright,
silvery spot will be evident if shielding is effective. Figure 39 shows effects of shielding gas contamination on
titanium weldments.
7.2 Purging
7.2.1 Purpose of Purging. The purpose of purging is
to replace unwanted air and other vapor contaminants
from the backside of the weld root by a gas that prevents
oxidation during welding (see Figure 40).72 Oxidation
can produce a variety of problems such as root oxidation
(sugaring), incomplete fusion, porosity and changes in
71. AWS Welding Handbook, 8th Edition, Volume 2: p. 102.
72. See AWS D18.2:1999, Guide to Weld Discoloration Levels
on Inside of Austenitic Stainless Steel Tube.
70. SCFH = standard cubic feet per hour; SLPM = standard
liters per minute; SCFM = standard cubic feet per minute.
50
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
DISCOLORATION FROM CHILL BLOCKS
IS EXPECTED AND IS ACCEPTABLE
1. ACCEPTABLE—NO DISCOLORATION IN
WELD OR HEAT-AFFECTED ZONE
2. NOT ACCEPTABLE—WHITE DEPOSITS IN
WELDS (ARROWS)
3. NOT ACCEPTABLE—BLUE COLOR IN
WELD AND HEAT-AFFECTED ZONE
(ARROW)
4. NOT ACCEPTABLE—BLUE COLOR
THROUGHOUT HEAT-AFFECTED ZONE
5. NOT ACCEPTABLE—SEVERE
DISCOLORATION
Figure 39—The Effects of Shielding Gas Contamination on Titanium Weldments
(Color Chart for Titanium Welding Acceptance)
51
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Figure 40—GTAW Weld Underbead Contamination with
Various Levels of Oxygen Contents in the Purging Gas
weld metal chemical composition, which can affect the
weld metal’s mechanical and corrosion properties.
Purging is recommended when welding stainless
steel, nickel alloys, and most nonferrous base metals.
Purging is usually not required when welding aluminum,
carbon steels and some low alloy steels. Purging is beneficial in reducing scaling when welding carbon steel hydraulic lines.
The tube shown in Figure 40 was prepared by making
10 full-penetration autogenous welds on the outside diameter of a 2 in. [50 mm] 316L stainless steel tube. Welds
on 304L tubing showed no significant difference in heat
tint from 316L. The torch shielding gas was 95% argon,
5% hydrogen (with <6 ppm of oxygen, moisture, and hydrocarbons) to assure full-penetration welds. The hydrogen addition to the torch shielding gas is considered to
have no effect on the heat-affected zone (HAZ) heat-tint
oxide on the inside surface. To provide controlled
amounts of oxygen in the backing gas, medical-grade
compressed air was mixed with 99.996% min pure argon
(<5 ppm of oxygen, moisture, and hydrocarbons). The
oxygen content was measured with a calibrated commercial oxygen indicator. The amount of oxygen in the backing gas was measured to be as follows:
No. 1—10 ppm
No. 2—25 ppm
No. 3—50 ppm
No. 4—100 ppm
No. 5—200 ppm
Combinations of argon and helium are used in selected
applications. Nitrogen is not a chemically inert gas but
has been used with success in purging austenitic stainless
steel, carbon steel, copper and low alloy steel. Nitrogen
should not be used to purge reactive alloys.
CAUTION
Hydrogen and hydrogen mixes are not used for
purging because of the potential explosion and fire
hazard.
7.2.3 Preparation for Purging. The weld root should
be isolated by means of dams or other suitable containment devices. Purging requires entrance and exit openings through which the purging gas can enter and exit the
weld joint area at controlled rates. When argon is used,
the gas inlet should be located lower than the exit opening to prevent entrapment of air. Where lighter than air
gases are used for purging, such as nitrogen, helium or
mixtures where helium is the major component, the inlet
gas opening should be higher than the exit. It should also
be noted that the size of the exit port must be equal to or
greater than the entry to prevent pressure increase. Special precautions must be taken to ensure that all leak
paths are blocked and areas where air may be entrapped
are well vented. Where open root weld joints are used,
tape may be placed over the joint to eliminate air from
re-entering the purged system and to reduce purging gas
losses. The tape should be peeled back as the weld is
made.
No. 6—500 ppm
No. 7—1000 ppm
No. 8—5000 ppm
No. 9—12 500 ppm
No. 10—25 000 ppm
7.2.2 Types of Purging Gases. Argon and helium,
being chemically inert, can be used as purging gases with
all gas shielded welding processes and base metals.
Argon is commonly used in the United States due to its
lower cost and ample supply. Helium is not commonly
used for purging due to low gas density and higher costs.
7.2.4 Purging Flow Rates. The purge flow rate is
based on the volume to be purged. A general rule of
thumb is to purge at flow rates and times that will
52
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
produce 5 to 10 system volume changes. The recommended maximum flow rate is a function of the volume
and shape to be purged. Typically it should not exceed
90 SCFH [45 SLPM].
Reasonable purge flow rates and times can be estimated from calculations of the system volume and by applying time factors. The time for one system volume
change is found by dividing “the system volume” by “the
purging gas flow rate.”
For example, the purge time for one volume change in
a 20 ft [6 m] length of 18 in. [450 mm] diameter pipe
purged at 50 SCFH [25 SLPM] would be:
Volume
On applications where the joints are taped closed during
the purge procedure, it is common for the welder to remove only enough tape to permit access for welding relatively short lengths of weld at a time when welding pipe
greater than 4 in. [100 mm] in diameter.
7.2.5 Purge Gas Exhaust. Provisions for an adequate
vent or exhaust are important to prevent excessive pressure build-up during welding. The area of vents through
which the back-up gas is exhausted to the atmosphere
should be at least equal to the area of the opening
through which the gas is admitted to the system. Extra
care should be taken to assure the back-up purge exhaust
is not excessive when welding the last inch or two
[25 mm to 50 mm] on the root pass.
= Cross-sectional Area u Length
= Pi u (Radius)2 u Length
= (Pi/4) u (Pipe Diameter)2 u Length
= 0.785 u (1.5 ft)2 u 20 ft
= 35.3 ft3
= Rate u Time.
Volume
= Rate u Time, therefore:
Time
= Volume/Rate
= 35.3 ft3/50 SCFH
= 0.70 hours or
= 42 min for one volume exchange.
7.2.6 Methods of Purging. Several examples of
methods or techniques of purging are given below.
7.2.6.1 Purging of Pipe or Vessel. The most common method for purging pipe consists of blanking off the
flanges or ends of the piping system as shown in Figure
42. Tape (duct, masking, or similar) is often used, but
blanks may be made from sheet metal, plastic, plywood,
heavy paper, or cardboard. When using wood, it is suggested that it be wrapped in a material that will minimize
air/moisture transmission. The purge gas is introduced
through one of the blanks and then vented through to one
or more of the other blanks. The gas inlet and venting locations are chosen so that the joints to be welded are located between the inlet and venting locations. Venting
must be adequate to eliminate dead air pockets in the system and to prevent the “closure” or “tie in” of the root
pass from blowing out (see Figure 43).
When the purge gas is heavier than air (e.g., argon), it
is preferable to admit the gas at the lowest point and to
vent at the highest point in the system in order to displace
the atmosphere upward.
When the purge gas is lighter than air (e.g., helium
and nitrogen), it is preferable to admit the gas at the highest point and to vent at the lowest point in the system in
order to displace the atmosphere downward.
Due to the size of the purge volume, and the amount of
time needed for purging, consideration should be given to
purging cost. The calculations above are guides to help
estimate the purge time; but it is recommended that residual oxygen measurements, using an oxygen analyzer, be
taken prior to welding to ensure purge purity. Figure 4173
shows recommended purging times for various pipe sizes.
After purging is completed, the flow of purge gas
prior to welding should be reduced until only a slight
positive pressure74 exists in the purged area to avoid pressure increase in the system. Excessive pressure can cause
root concavity and porosity in the root pass. After the
root and first filler passes are completed, the purge can
sometimes be discontinued. However, care must be taken
to avoid premature discontinuation of the purge. In many
instances where corrosive environments are involved, the
oxidation/heat tint that occurs once the purge has been
discontinued, leads to premature corrosion failure.
When welding with consumable inserts, where the
unfused insert seals the joint root and prevents the escape
of purge gas, flow rates on the order of 8 SCFH–12 SCFH
[3.5 SLPM–6 SLPM] are typical. Flow rates of 15 SCFH–
18 SCFH [7 SLPM–9 SLPM] are typical for joints having
open roots. For small diameter pipe and tubing, it may be
necessary to reduce the flow rates below the values stated.
7.2.6.2 Removable Plugs. The volume of pipe that
must be purged can be reduced by inserting removable
plugs into the pipe assembly on one or both sides of the
joint to be welded (see Figure 44).
7.2.6.3 Removable Chamber. A removable isolating chamber device can be inserted into the piping assembly beneath the joint to be welded so that the joint is
isolated (see Figure 45). This can significantly reduce the
volume to be purged.
73. Data from AWS D10.4-86, Recommended Practices for
Welding Austenitic Chromium-Nickel Stainless Steel Piping and
Tubing,” Figure 4, p 17.
74. To reduce the back diffusion of air into the purged system.
7.2.6.4 Purge Distributor Ring. Use of purge distributor rings is a method that can be used for purging
welds in large diameter pipe (such as 12 in. [300 mm]
53
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Preweld purge time for 12 in. [300 mm] of pipe at a flow rate of 50 ft3/hr (23.5 L/min].
To calculate the purge time for any length of pipe, multiply the value obtained from the chart by the length of the pipe. For example, For
finding the time to purge 200 ft [60 mm] of 5 in. [127 mm] pipe, the chart indicates 1 min is required for 12 in. or 1 ft [300 mm] of pipe
length. Thus, 200 ft [60 m] of pipe length requires 200 x 1 min, which equals 200 min or 3 hrs and 20 min.
Figure 41—Purging Times for Various Pipe Sizes
and over) as shown in Figure 46. This method consists of
placing a ring, made from a small diameter pipe containing numerous small holes around the periphery, beneath
the joint. This arrangement distributes the purge gas to
the underside of the joint.
the joint opening to permit the joint to be tacked. After
tacking, peel back the tape as the root pass is welded
leaving approximately 1 in. [25 mm] at the tube not
welded. Complete the second filler pass to this point, then
remove the tube and tape and then complete the root and
filler pass as soon as possible. Follow the manufacturer’s
directions for flushing out the water-soluble dams.
7.2.6.5 Soluble Paper Dams. When a piping system permits water flushing after welding, dams made
from water-soluble paper and tape may be used to contain the purge. The water-soluble paper is placed on both
sides of the weld joint. In this scheme, the joint opening
is covered with masking tape and the purge is introduced
into the pipe through a long, small diameter tube, which
is inserted through the tape covering the joint opening
(see Figure 47). After purging, remove enough tape from
7.2.6.6 Backing Channel. In welding sheet or
plate, the purge may be introduced through a channel
held beneath the joint as shown in Figure 48. The channel is covered at both ends, and gas is admitted through
the perforated pipe inside the channel. Gas is vented
through the weld joint and the unsealed edges of the
channel.
54
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 42—Purging a Piping System with Open Ends Blanked
General Note: The total area of all vents should approximate the area of the inlet.
Figure 43—Purging of a Piping System with Appropriate Venting
to Eliminate Dead Air Pockets
55
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 44—Purging with Removable Plugs
Figure 45—Purging with Removable Chamber
Figure 46—Purge Distributor Ring
56
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 47—Purging with Water Soluble Paper Dams
Figure 48—Purging with a Backing Channel
57
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 49—Purging with a Gas Distributor (Diffuser)
Figure 50—Typical Inert Gas Glove Box Chamber
7.2.6.7 Purge Distributors. Another method for
purging sheet or plate during welding uses a length of
pipe having numerous small holes that is placed beneath
the joint as shown in Figure 49. The holes in the pipe are
located so as to distribute the purging gas over and under
the surface of the joint.
vision for containing the pieces to be welded in a glove
box containing sight glasses, glove ports, etc. or in a
plastic “bubble.” After the parts have been put in the
chamber, purging is begun, and readings can be taken
with oxygen and moisture analyzing instruments to
assure that welding is not started until the oxygen content
is at a suitable low level, usually less than 20 ppm. In
some special applications, such as welding of stainless
steels in the pharmaceutical industries, the glove box
inert gas atmosphere must be maintained at less
than 10 ppm oxygen in order to produce the ultra-clean
internal tube surface finishes required. Still in other
industries, such as the manufacture of semiconductor
components, it is required that the inert atmosphere be
7.2.7 Additional Methods of Purging
7.2.7.1 Glove Boxes and Bubbles. Maximum benefits can be obtained when the entire object to be welded
can be placed in a controlled atmosphere chamber (glove
box). Such chambers, as shown in Figure 50,75 have pro75. Photo courtesy of Vacuum Atmosphere.
58
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
less than 1 ppm. High purity atmospheres can produce
improved properties.
welding (e.g., weld lathes or tube mills) fixed barriers or
shields may be built into the fixturing.
7.2.7.2 Flexible Purge Bags. When size, configuration, or location of welds to be made preclude welding in the rigid chamber, “bag” welding may be done. In
this technique the piece to be welded is enclosed in a
clear vinyl plastic bag, 0.004 in.–0.006 in. [0.1 mm–
0.16 mm] thick, and of sufficient optical quality to see
through (see Figure 51). The atmosphere in the bag is
evacuated, and the “bag” or “pillow” is inflated with
argon. The GTAW torch is introduced through a small
slit that is cut in the bag, and the weldment is submerged
in the argon atmosphere inside of the bag.
7.2.8 Backing Methods. In addition to trailing shields
and backing channels noted above, other methods to
“back-up” the weld and minimize oxidation are used.
These include fluxes and backing tapes.
Commercial fluxes are available for backing welds, in
lieu of purging, when welding stainless steels, alloy
steels, and high nickel alloys. Each of these groups of
materials requires a specific type flux. (This method is
not as effective as purging with an inert gas and is prohibited in many high-purity applications.) The user is
cautioned to evaluate the compatibility of the flux with
the material to be welded and the temperature and the
service in which the weldment will be used.
Backing tapes generally consist of a thick, dense mass
of woven refractory fibers or ceramic segments affixed to
the centerline of an adhesive coated high temperature
tape. The backing tapes are quick to apply and easily
used on complex shapes. They are widely used on onesided welding where a smooth, convex underbead is
desired (see Figure 55).
7.2.7.3 Trailing Shields. Trailing shields may be
necessary. For example, with titanium, the use of a trailing shield ensures inert gas coverage over the weld area
until the molten metal has cooled to the point that it will
not react with the atmosphere. Two types of trailing
shields using porous stainless steel material are shown in
Figures 52 and 53 for circumferential and straight joints,
respectively. A third type of trailing shield is shown in
Figure 54. In semiautomatic and automatic machine
Figure 51—Flexible Plastic Purge Bag
59
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 52—Trailing Shields. Bottom View of Inert Gas Trailing Shield Fabricated
Using Stainless Porous (100 micron) Tubing (Shown with High Temperature Tape)
Figure 53—Trailing Shields. Inert Gas Trailing Shield Fabricated Using
Stainless Porous (100 micron) Tubing (Shown with High Temperature Tape)
60
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 54—Trailing Shields—Inert Gas Trailing Shield
Fabricated Using Stainless Porous (40–100 micron) Sheet Metal
Figure 55—Shielding with the Use of a Backing Tape
7.2.9 Comments on Materials Used in Gas Recirculating, Purging, and Distribution Systems. All rubber
and plastic materials (e.g., hoses and flexible bags) allow
permeation of significant levels of atmospheric oxygen
and moisture (e.g., into the hose or flexible bag). Permeation of oxygen or moisture occurs even in systems
under pressure (e.g., gas hoses) because it is dependent
not upon the total pressure of the system but rather upon
the difference in partial pressures or concentration of the
contaminant (e.g., oxygen or moisture) inside and outside the system. For example, the partial pressure of oxygen inside a hose may be 20 ppm, but it is in a location
where there is 210 000 ppm on the outside of the hose
(i.e., air contains 21% oxygen). Thus there is a tremendous driving force for oxygen to diffuse (permeate) into
the system.
As the permeation rates for moisture can be easily 10
to 100 times greater that the permeation rates for oxygen
for most plastics, simply measuring the oxygen content
of a glove box is not necessarily sufficient. The moisture
content must also be measured.76, 77 Moisture levels inside flexible glove boxes (glove bags) can easily exceed
1000 ppm. Even a thoroughly purged box with all metal
sides and a single front panel made of plastic (such as
acrylic or polycarbonate) can easily contain 10 ppm–
50 ppm oxygen and 50 ppm–500 ppm moisture during
use.
For welding of titanium and other reactive metals, it is
recommended that glove boxes be made of all metal
76. Bhadha, P. 1994. “Control of Moisture and Contaminants
in Shielding Gases.” Welding Journal, Vol. 73, No. 5, May
1994, pp. 57–63.
77. Bhadha, P. 1999. “How Welding Hose Material Affects
Shielding Gas Quality.” Welding Journal, Vol. 78, No. 7, July
1999, pp. 35–40.
61
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
construction with glass (not acrylic) panels or ports.
Glove box gloves should be made of butyl rubber rather
than nitrile rubber. Although nitrile rubber is softer and
provides more flexibility of motion, nitrile rubber also
allows four (4) times as much permeation of atmospheric
moisture as butyl rubber.
Because of the difficulty in purging atmospheric air
and moisture from dead pockets inside large metal glove
boxes, it is recommended that parts be transferred via a
vacuum-capable antechamber. The antechamber must be
subjected to alternate vacuum and pressurization (with
an inert gas) cycles. A minimum of three, preferably five
pressure/vacuum cycles with a vacuum greater than
25 in. [625 mm] Hg are recommended.
Table 15
Gas Purity Specification by Industrial
Grade(1)
Grade
6.0
5.5
5.0
4.8
4.7
4.5
4.0
Grade
by “9”s
Six “9s”
Five “9s”
Four “9s”
Minimum
Purity(2)
(%)
Maximum
Impurities(2
(ppm)
99.9999%
99.9995%
99.999%0
99.998%0
99.997%0
99.995%0
99.99%00
1
5
10
20
30
50
100
Notes:
(1) Grades by “trade” names (e.g., high purity, etc.) may vary with the
suppliers.
(2) If the purity is determined by the difference method, then the results
reported may have excluded some gases/elements.
7.3 Shielding and Purging Gas Purity. The quality of
the welds made by GTAW will depend on the purity of
the shielding and purging gas as well as the control of the
other variables. Data on gas purity levels are shown in
Tables 15–18. Purification of the shielding and purging
gas at the point of use ensures consistency within the
limits of the purification. Regardless of the alloy system
being welded, the purer the gas delivered to the welding
process the more consistent will be the results. See additional notes on gas purity in 7.3.5 and 7.5. Additional information is contained in AWS A5.32.
99.950% to 99.995%. Table 16 lists the purity levels for
different grades of argon. For some commercial applications, the minimum purity limit is typically 99.950% argon. Often a higher purity argon is not only desirable but
also required, either by the process application or by the
product specification. For example, military applications
may often require a minimum argon purity level of
99.985%, a maximum oxygen content of 50 ppm and a
dew point of –65°F or lower temperature. The dew point
is a measure of the temperature at which water vapor
begins to condense from a gas at atmospheric pressure.
In effect, the dew point is a measure of the quantity of
7.3.1 Argon (SG-A). Welding grade argon is refined
to a “high purity” and is defined in AWS classification
SG-A as having a minimum purity of 99.997% in the
gaseous state. The term “high purity” may have different
definitions when comparing other standards and/or gas
suppliers. “Standard” welding grade as defined by different suppliers and end users can vary from as low as
Table 16
Purity Requirements for Gaseous Argon
Standard(1)
Grade/Quality
Level
Minimum %
Mole/Mole
Water,
Max. ppm
Oxygen,
Max. ppm
Dew Point,
Max. °F
Dew Point,
Max. |°C
Other Gas,
Total ppm
B
C
C
A
C
C
C
C
All
A
B
SG-A
C
D
E
F
99.9850
99.9850
99.9960
99.9970
99.9970
99.9980
99.9990
99.9995
(2)27.5(2)
50
50
7
(1) n/s (3)
5
2
1
2
–65
–65
–72
–76
–76
–90
–100
–104
–54
–54
–58
–60
–60
–68
–73
–76
100
100
21
n/s
24
14
8
14
23.0
14.3
10.5
10.7
3.5
1.5
1.0
Notes:
(1) Standard A = AWS A5.32/A5.32M-97, Specification for Welding Shielding Gases.
Standard B = MIL-A-18455-C (Dept. of Defense Specification).
Standard C = CGA G-11.1-1992 (Compressed Gas Assn. Commodity Specification).
(2) Converted from Requirement of 0.02 mg/L.
(3) The symbol n/s means limits are not specified.
62
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 17
Purity Requirements for Gaseous Helium
Standard(1)
Grade/
Quality
Level
Minimum %
Mole/Mole
Water,
Max. ppm
Oxygen,
Max. ppm
Dew Point,
Max. °F
Dew Point,
Max. |°C
Other Gas,
Total ppm
B
B
C
C
C
A
C
C
C
C
C
A
B
H
J
K
SG-He
L
M
N
P
G
99.995
n/s
97.500
99.000
99.990
99.995
99.995
99.995
99.997
99.999
99.999
n/s(2)
n/s
n/s
n/s
n/s
15
15
9
3
. 1.5
Note (5)
n/s
n/s
n/s
n/s
n/s
n/s
5
3
3
1
Note (5)
n/s
n/s
n/s
n/s
n/s
–71
n/s
n/s
n/s
–100
n/s
n/s
n/s
n/s
n/s
–57
n/s
n/s
n/s
–73
n/s
(2)50(3)
n/s
n/s
(2)10(4)
n/s
n/s
n/s
79
30
9
Note (5)
Notes:
(1) Standard A = AWS A5.32/A5.32M-97, Specification for Welding Shielding Gases.
Standard B = BB-H-1168B (Federal Specification).
Standard C = CGA G-9.1-1992 (Compressed Gas Assn. Commodity Specification).
(2) The symbol n/s means limits are not specified.
(3) Total of all impurities.
(4) Carbon Monoxide = 10 ppm maximum.
(5) Sum = 1 ppm maximum.
Table 18
Purity Requirements for Gaseous Hydrogen
Standard(1)
Grade/
Quality
Level
B
B
C
C
A
C
C
C
C
C
C
Type I
Type II(4)
A
B
SG-H
C
D
E
F
L
M
Minimum % Water, Max. Oxygen, Max. Dew Point,
Mole/Mole
ppm
ppm
Max. °F
99.000
99.500
99.800
99.950
99.950
99.950
99.990
99.995
99.995
99.999
99.9997
Note (2)
Note (2)
Note (2)
32.0
32.0
7.8
3.5
3.5
1.5
3.0
0.2
n/s(3)
n/s
n/s
10
n/s
10
5
5
1
1
0.2
n/s
n/s
n/s
–60
–60
–80
–90
–90
–100
.0 –92.5
n/s
Notes:
(1) Standard A = AWS A5.32/A5.32M-97, Specification for Welding Shielding Gases.
Standard B = BB-H-886-B (Federal Specification).
Standard C = CGA G-5.3-1990 (Compressed Gas Assn. Commodity Specification).
(2) None condenses.
(3) The symbol n/s means limits are not specified.
(4) Type II is liquid state.
63
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
Dew Point,
Max. °C
Nitrogen,
Max. ppm
Other Gas,
Total ppm
n/s
n/s
n/s
–51
–51
–62
–68
–68
–73
–69
n/s
n/s
n/s
n/s
400
n/s
400
25
20
2
2
2
3000
3000
30
30
n/s
34
.06.5
1
.00.5
5
.00.6
AWS C5.5/C5.5M:2003
water vapor present. In this way it is often used to assess
gas purity since it is relatively easy to do, as compared to
a quantitative chemical analysis (see Table 12).
For reactive metals (e.g., titanium) and refractory alloys
and/or special applications, a “very high purity” argon is
required because contamination of the weld in these alloys
can degrade not only the corrosion resistance but also the
mechanical properties. The term “very high purity” may
have different purity definitions when comparing different
gas suppliers. For titanium a minimum purity of 99.997%,
a maximum moisture content of 10 ppm and a dew point
of –76°F [–60°C] or lower is recommended. For very
high/ultra high purity applications such as bio-tech, aerospace, and semiconductor industries the purity levels are
often specified significantly higher, such as 99.999%. An
example of “ultra high purity” is in the semiconductor
industry SEMI Specification E49.6 which requires a maximum impurity level of 0.25 ppm.
Many alloys, such as titanium, stainless steel, and
nickel alloys for high-purity applications, are fabricated
in chambers from which all traces of air have been purged
prior to initiating the welding operation. Figure 40 illustrates the effects of chamber oxygen content on gas tungsten arc weld underbead contamination in stainless
steels.78 Gross discoloration occurred with 200 ppm oxygen but little or no discoloration occurred with 57 ppm
oxygen or less. The discoloration with 200 ppm oxygen
level may be sufficient to cause corrosion problems.
purging gas. It is less frequently used as the gas that initiates or maintains the arc. This purity is acceptable for
general purpose shielding and purging of copper base alloys, nickel base alloys, austenitic stainless steel, carbon
steel and low alloy steel. Irrespective of the purity, nitrogen shielding of alloys other than those listed above
should be done only after in-depth investigation. Nitrogen shielding should not be used for the reactive metals.
The main attraction of nitrogen is its lower cost compared
to both argon and helium. Depending upon quantity of
the gas being utilized, nitrogen gas is often less than half
the cost of argon and can be one-fifth the cost of helium.
Note: Pre-mixed blends can contain significantly higher
levels of oxygen as compared to the pure gases (e.g., argon, helium or hydrogen). Air leaks during the mixing process are the major cause of this discrepancy. Stratification
of contents, from settling of the heavier components is also
a possibility, resulting in a changing blend concentration.
7.3.4 Hydrogen (SG-H). Welding grade hydrogen is
refined to slightly lower purity levels than the inert gases
(see Table 18). (AWS A5.32 defines AWS classification
SG-H as having a minimum purity of 99.95% in the gaseous state and 99.995% in the liquid state). The main reason for this is that the principal impurity of concern is
oxygen. Oxygen will react preferentially with hydrogen
(reaction rate increases as temperature increases) to form
water vapor rather than reacting with the metal being
welded. Section 11 provides additional information regarding which alloy systems can be welded using hydrogen additions. Hydrogen is rarely used by itself either in
the arc or as a shielding gas. It is NOT used for purging
or as a back-up gas for safety reasons (i.e., it is highly
flammable and can be an explosion hazard). Safety details are covered in Section 15.
7.3.2 Helium (SG-He). Welding grade helium is refined to a purity of at least 99.995% in the gaseous state
per AWS A5.32. Other purity-related information is
shown in Table 17 of this document. This level may be
usable for almost all alloy systems. For reactive metals,
such as titanium, pure helium is not frequently used due
to the increased difficulty of keeping the solidified weld
metal blanketed with an inert gas. Helium is not often
used in glove boxes or similar devices. Helium is frequently mixed with argon for greater depth to width ratio
welds. When mixed, the purity of the helium should be
equal to or better than that of the argon. The dew point
data in Table 12 can be used for mixtures of argon and
helium since individually or as mixtures they can be considered ideal gases.
7.3.5 Purity Specification. One measure of purity is
the “grade” of gas as expressed by the number of “nines”
in the percentage of purity. See Table 15 for these purity
conversions. The reader is cautioned that the “grade”
may not give the “purity” that one thinks one is getting.
For example, the stated grade may exclude a particular
gas (e.g., argon in nitrogen) from the measurement difference from 100%. A detailed, definitive discussion of
welding gas purity is beyond the scope of this document.
The reader is encouraged to review additional reference
sources. For example, “Measurement and Definition of
Gas Purity,”79 by Krippene, et al., gives a summary of
the subject.
7.3.3 Nitrogen (SG-N). Welding grade nitrogen is
usually refined to a purity of at least 99.998%. (AWS
A5.32 defines AWS classification SG-N as having a minimum purity of 99.9% in the gaseous state and 99.998%
in the liquid state.) Nitrogen is widely used in Europe as a
78. See also Tapp, J., McKeown, M., and Stanes, I. “Reduced
Oxygen Levels During Welding Improve Stainless Steel Corrosion Resistance,” Tube International, Vol. 13, No. 59, March
1994.
79. Krippene, D. T., Kurek, W. T., and Samuels, S. L. 1989.
Measurement and Definition of Gas Purity. American Laboratory, September 1989.
64
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
When specifying gas purity, it is important to distinguish between the “assay” and the “total purity” values;
and, whether or not the total purity value is a “total purity
by difference” (TPD). Assay is defined by direct measurement of the major components. Total purity is a
means of defining gas purity by measuring certain impurities or minor components and subtracting from 100%.
Products from different vendors and different products
from the same vendor, when reported by the “nines values” (e.g., 99.995%), may have been derived by different
methods of analysis.
all purifiers), do not eliminate the need to properly purge
and shield the weld zone; sufficient pre-flow and postflow shielding gas should be maintained.
7.5.1 Reactive Resins. Reactive resin purification can
be designed to remove a wide range of impurities including moisture, oxygen, hydrocarbons, carbon dioxide and
many other impurities in the welding gas. The life of the
active element depends upon the volume of the impurity
that is passed through it, i.e., the cleaner the gas and the
gas system, the longer the life of the purifier. The reactive compound design varies with the manufacturer. For
example, Cu, Cr, Mn and Li products are known to be
available. These compounds form solid, nonvolatile reaction products that remain in the purifier. The gaseous byproducts of the chemical reaction and its effects on the
weld metal, if any, must be understood and considered by
the user. For example, if small amounts of hydrogen
were to be liberated in the reaction, it would most likely
be burned up in the arc, but if the same gas was used for
backing gas, the hydrogen might be absorbed by the molten pool and end up as porosity in the solidified metal or
cause hydrogen-induced cracking in the heat-affected
zone.
Some of the compounds used to purify the gases
change color as they are consumed. This color change is
useful for end-point detection to trigger alarms when the
purifier is no longer effective.
These systems usually do not require external heating
or cooling to operate or control the purification. Thus,
purification comes as soon as flow of gas is established
through the purifier. See Figure 56 for an example of this
type of purifier. Generally, the reactive compound systems are not regenerated, but may be, depending on the
reactive compound; they are usually replaced when the
reactive compound is no longer active.
In the reactive resin systems, the reaction times are
very fast (essentially instantaneous) and the gas flow rate
does not affect nor limit the purity level. The oxygen absorbing capacity (volume) of the different products varies with the chemical composition and size of the system
purchased. Flow rates of 100 SCFH [50 SLPM] are typically available, but higher flow rates can be designed. For
example, systems capable of flow rates up to 2000 SCFH
[950 SLPM] are available in the semiconductor industry.
These systems are lightweight and can be portable.
The safety aspects of these systems need to be considered. For example, if compressed air or oxygen or an ArCO2 mixture were to be passed through the reactive
resin, sufficient heat can be generated to fuse or char
the resin and perhaps decompose the resin into its basic
by-products. Some resins are designed to minimize or
eliminate this problem. The MSDS sheet and other information should be studied carefully to determine the exact
safety cautions that should be exercised.
7.4 Shielding and Purging Gas Economics. Argon is
the most economical torch shielding gas and can be used
for welding most materials, including refractory/reactive
materials. Helium is not as widely used as argon due in
part to its higher cost. Although cost varies substantially
with quantity, a rough comparison would be: if bulk (liquid) argon = X, then cylinder argon = 1.5X and cylinder
helium = 2.5X. Due to its higher cost, helium is not normally used for purging or back-up purposes. Nitrogen is
the most economical purging gas and can be used as a
root shielding gas for steels. However, it is not inert and
may produce nitrogenization of the weld metal. In austenitic stainless steel this can produce a decrease in the ferrite content, which may increase hot cracking. Nitriding
of the root bead in some steels could render them more
hardenable. Care should always be exercised when using
nitrogen as a root purging gas to ensure that detrimental
metallurgical effects do not occur.
Methods to reduce purging gas costs include: a) eliminating the purging (backing) gas after the root and first
filler passes have been completed if this will not be detrimental to the weld’s service, and b) reducing the volume
to be purged by using dams, plugs, collapsible bags, etc.
7.5 Purifiers. Contamination of shielding gases, usually
by moisture, air, and/or hydrocarbons from gas compressors adversely affects many welding properties. Variability in shielding and backing gas quality can come from
many sources, including contaminated gas cylinders or
bulk storage tanks, cylinder to cylinder purity variations
and/or manifold/piping/delivery system, and other component leaks in the flow control equipment.
One solution is to purify the shielding gas at the point
of use (POU); in welding this is as close to the torch as
possible. A variety of gas purifying systems are commercially available, many of these are spin-offs from the gas
purification technology used in semiconductor manufacturing. These systems typically use a high-surface-area,
reactive material to react with the gas impurities. These
systems require regeneration or replacement of the active
elements at intervals to maintain their effectiveness. The
investment in any purification system must be weighed
against the benefits. Purifiers, in general (this applies to
65
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 56—Point-of-Use (POU) Purifiers
(Waferpure® Reactive Resin Type) Below a Welding Fixture
7.5.2 Heated Metal Getters. These systems are usually designed to react with specific compounds like H2O,
O2, CO, CO2, H2, N2, and hydrocarbons. These systems
contain reactive compounds of titanium or alloys of
zirconium or vanadium. See Figure 57 for an example of
these systems. The heated metal getter system, when operating at normal welding flow rates, can be quite large
in volume (size). The time to “scrub” the gas is usually
dependent upon temperature of the sieve compound as
well as the level of impurity. The smaller cartridge units
can be limited to flow rates as low as 1 SCFH
[0.5 SLPM]. Larger systems are available to handle the
typical welding gas flow rates of 21 SCFH [10 SLPM].
End point detection is typically not built into the system
to determine when the getter needs regeneration. The
economics of these large systems need to be studied
carefully. Operating temperatures as low as 750°F
[400°C] or as high as 1300°F [720°C] or more may be
required to purify at the desired levels. These systems are
generally not portable. Very large systems are typically
required to remove reactive impurities, such as nitrogen
and carbon monoxide.
The safety aspects of these systems need to be considered. If compressed air or oxygen were to be passed
through the hot getter bed, sufficient heat can be generated to melt the entire system.
66
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
typically not built into the system to determine when the
sieves need regeneration.
7.6 Purging Gas Safety. 80 It is not possible to list each
gas mixture that may be encountered. In general, labels
should be checked to identify those that are classified as
flammable or as oxidizers. Mixtures of inert gases should
be handled with the same precautions as argon, carbon
dioxide, helium or nitrogen.
Argon, helium, hydrogen and nitrogen are odorless,
colorless and tasteless. All can cause rapid asphyxiation
and death in confined, poorly ventilated areas. Any atmosphere containing less than 18% oxygen will cause dizziness, unconsciousness or possible death. Use an oxygen
analyzer with an adequate scale range and alarm to check
for adequate oxygen prior to entering a room, tank, enclosed fixture or other confined space.
Argon and nitrogen supplied in liquid form require
the same precautions. Additional care should be taken to
avoid exposure to the cold gas or liquid, which may
cause severe frostbite to exposed parts of the body, especially to the eyes. Do not touch frosted pipe or valves. If
exposure to these cryogenic liquids or cold gases does
occur, immediately contact a physician or seek other first
aid.
Hydrogen is an odorless, colorless, tasteless gas.
Being the lightest element, any escaping hydrogen has a
tendency to rise to the highest elevation in an enclosed
area. Hydrogen is a flammable gas, and burns with a
nearly invisible flame. Mixtures with oxygen or air in an
enclosed room or area can explode if exposed to any
source of ignition, spark or flame. Since it is odorless, it
is not possible to detect a concentration of hydrogen by
smell. Be sure to keep all areas where hydrogen is used
well ventilated. In hydrogen mixed gases, hydrogen
could possibly stratify or separate in cylinders, manifolds, etc. and could cause an explosion or fire.
When a question arises regarding the proper handling
or storage of a gas, contact your safety department or the
supplier of the gas cylinders. A simple status tag as
shown in Figure 58, if used properly, for example can
help minimize the number of empty cylinders in the
shop.
Never identify a gas by the color of the cylinder, as
there is no standard code on cylinder colors, and some
cylinder colors change when exposed to light. ALWAYS
READ THE CYLINDER LABEL. Gases should always be referred to by their proper names. They should
not be referred to as “Air.” Compressed air is a specific
product.
Figure 57—Point-of-Use Gas Purifier
(Heated Metal Getter Type)
7.5.3 Molecular Sieves. Molecular sieves typically
remove only moisture but not oxygen (sieve types 4A
and 5A) and sometimes carbon dioxide (sieve type 13X)
depending on the pore size of the sieve compound. This
type of purifier requires activation (heating)/regeneration
to remain effective. The volumes needed are typically
large for welding gas flow rates. End point detection is
80. Additional information is contained in AWS A5.32. Further
information may be available from the Compressed Gas Association or from the welding gas suppliers.
67
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
-
remedy for this would be to either nickel plate the tool or
fabricate it from an austenitic stainless alloy. Low alloy
and carbon steels may be used for certain tooling applications but due to their tendency to oxidize (rust) and
their magnetic properties they must be carefully used.
Storage of tooling is important, as it must be kept in a
clean dry area. Cleaning of weld tooling prior to use is
important regardless of the material from which it is
made. Magnetic materials used for weld tooling can
contribute to a condition known as arc blow, which is
deflection of the arc from its normal path as a result
of magnetic forces. Materials that contain iron, nickel
and/or cobalt can be magnetized or affected by a
magnetic/electromagnetic field.
Due to some of the aforementioned conditions it is
highly recommended that weld tooling be made from
quality material, which is an important part of the overall
effort required to make high quality weldments. The use
of nonmagnetic material such as copper, aluminum or
austenitic stainless steel is suggested to reduce the effects
of magnetic forces, and as mentioned prior, certain tooling may be nickel flashed to reduce contamination and
eliminate oxidation.
CYLINDER
TAG
MAINTAIN 50 PSIG MINIMUM
SECURE TANK PROPERLY
FOLLOW ALL SAFETY PRECAUTIONS
RETURN TO VENDOR
IN SERVICE
FULL
Figure 58—Cylinder Status Tag
(The Use of a Simple Tagging
System Can Be Very Helpful)
8.1.1 Principles Governing Fixture Design. The decision to use fixturing for the fabrication of a weldment
is governed by economics and quality requirements. The
proper use of fixturing, including heat sinks, can reduce
welding time and can be the difference between success
and failure of the welding operation. The one-time fabrication of an assembly may not justify the use of fixturing; however, the fabrication of a larger number of
assemblies could easily justify the use. Also, high quality
work may dictate that fixturing be used to maintain and
control close dimensional tolerances for either design or
nondestructive examination requirements. A decision not
to build fixturing usually means that the part to be
welded can be fitted and tack welded together with the
resultant structure to be self-supported during welding.
After welding, the resultant distortion can either be tolerated or corrected by either thermal or mechanical
straightening. Care should be taken to avoid excessive
restraint, which can result in weld cracking.
The primary functions of fixtures are:
(1) To locate parts relative to an assembly
(2) To maintain alignment during welding
(3) To control distortion in the weldment
HAZARD ALERT
If a person accidentally enters an enclosed area and
becomes dizzy or unconscious do not enter the area to
render aid unless equipped with an oxygen breathing
apparatus or mask with a fresh air supply. Rescue attempts should only be conducted by a trained team of
a minimum of two persons; the backup person should
not enter the room, but remain outside the area to provide assistance in the removal of the victim.
8. Fixturing and Tooling
8.1 Material Selection. When designing, specifying and
fabricating weld tooling, careful selection of its material
must be made. This can be accomplished by reviewing
the part and/or assembly requirements relative to part
material type, its thickness or mass and its thermal conductivity. Dimensional tolerances of the finished part and
its function must also be considered as it may influence
tooling design and material choice.
Another important issue is to consider if the tooling
could react adversely with the part material. An example
of this condition is that the workpiece can be contaminated with copper or braze material from the tooling. A
8.2 Tooling/Fixturing Considerations
8.2.1 Heat Control and Cooling. Welded materials
may suffer severe distortion or even burn through unless
the heat generated by the welding arc is removed from
the joint as rapidly as possible. This is especially true
when welding thin gauge materials.
68
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Heat sinks to accomplish rapid dissipation of welding
heat are generally manufactured from either copper or
aluminum. In certain applications, rapid removal of
welding heat can be assisted by water-cooled weld tooling. This is usually accomplished by circulating water
through passages in the tool for this purpose. In rare
cases, water can be very carefully sprayed on the tooling
to assist heat removal.
likely fabricated with temporary or even expendable
tooling. If it were a close tolerance job or one with many
pieces to be processed, it would most likely dictate
permanent or hard tools or fixtures.
Welding tooling can be as simple as using a C-clamp to
large exotic fixtures (refer to Figure 60) that may be required for the nuclear or aerospace applications. Many
times, weld tooling can be fabricated on the job. Obviously
large exotic tools would usually require a formal design
and be manufactured by a tool and die type shop or department. Welding aids or tools that may be made up on the job
would fall into the category of temporary or soft tooling.
8.2.2 Distortion Control. Severe localized distortion
can occur due to the extreme differences in temperatures
of the weld metal, heat-affected zones (HAZ) and the
base metals. For example, Figure 59 illustrates a distorted weldment when fixturing was not used. Figure 60
shows an example of tooling to hold a component during
welding in order to control distortion.
Very thin materials will tend to distort more than
heavier weldments; thicker materials will normally require heavier restraints. Certain materials, due to their
coefficients of thermal expansion and contraction will
demonstrate greater distortion than others. Welding trials
conducted on representative test samples may at times be
required to determine what tooling is required to adequately control weldment distortion. Heat sinks can be
used to evenly distribute heat and hold the welded materials in place while cooling takes place.
8.3.1 Run-On/Off Tabs. Run-on and run-off tabs are
pieces of metal placed on either end of the weld joint on
which the weld is started and ended. These will insure
that the complete weld joint has been joined and that trim
allowance is not required. The tabs are usually tack
welded to the ends of the joint, but in some cases they
can be held in place with weld fixturing. Figure 61 is an
example of a strip weld with tabs. They are commonly
used with mechanized GTAW, but can also be used when
manually welding, especially on thin gauge materials.
The tabs should be made from the same material as the
parts being welded. For butt weld joints the tabs should
be the same thickness as the actual weld joint thickness.
For lap joint configuration, using tabs equal to the preweld lap thickness may be of some benefit. The accurate
fit-up between the tab and the weld joint of the material
being welded can prove to be a critical parameter. If
blowholes occur at the junction of tab to joint, then
greater control is required. Backing and shielding gas
can also impact the result of using weld joint tabs.
8.3 Temporary (Soft)/Permanent (Hard) Tooling.
Welding tooling and fixturing is sometimes referred to as
“soft” and “hard” or temporary and permanent. The type
of weldment, its requirements and the number of pieces
processed usually will influence the type of tooling selected and used. For example, a one-of-a-kind job that
has no or few tolerance requirements would be most
Figure 59—Weld Distortion in Ti-6AL-V Bead-on-Plate (Sheet) Weld
69
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 60—Tooling for GTAW of Fuel Cell Components to Control Distortion of Weldment
Figure 61—Run-On/Run-Off Tabs Used for Welding Ends of Strip Material
70
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
The procedure for using tabs is briefly outlined here.
The start (run-on) and run-off tabs are fixed in place. The
welding arc is initiated on the start tab, the joint is
welded and the arc is extinguished on the run-off tab.
After completion of the welding, the tabs are removed by
either cutting or grinding and in many cases can be reused several times before discarding.
pital beds to nuclear power plant piping and jet engines.
The process is used during original component manufacture or during component repair.
The manual GTAW process allows the skilled welder
to control the weld pool width and depth of penetration
by varying current level, arc length (voltage), travel
speed, and filler metal addition. GTAW is the preferred
arc process for joining thin gage metals and for making
welds close to heat sensitive components because it allows for the precise control of process variables. GTAW
is also used for small jobs and repair welding in many
fabrication shops because of the ease of control of the
process and the ability to add filler metal as necessary.
GTAW is used with or without filler metal to produce
high-quality welds with smooth, uniform shapes. The
GTAW process can also be used for spot welding in
sheet metal applications.
The process is used to weld most metals. It is especially useful for joining aluminum and magnesium,
which form refractory oxides, and for reactive metals
like titanium and zirconium, which can become embrittled if exposed to air (i.e., oxygen, moisture, and nitrogen) while molten.
GTAW is used to weld all types of joint geometries
and overlays in plate, sheet, pipe, tubing and structural
shapes. It is particularly appropriate for welding sections
less than 3/8 in. [10 mm] thick. Welding of pipe is often
accomplished using GTAW for the root pass and either
SMAW or GMAW for the fill passes.
The following sections will briefly describe equipment requirements and process techniques relative to
manual welding.
9. Welding Techniques
9.1 General. Prior sections have covered the principals
of the GTAW process, power source and auxiliary equipment, shielding and purging gases, and tungsten electrodes. These sections provide a sound foundation for
understanding the key elements of the GTAW process.
However, these sections have not tied the key process elements together and shown how the GTAW process is
applied in day-to-day shop operations. This section will
describe the different welding techniques and provide examples of how the GTAW process is applied to each
technique.
Definitions of the welding techniques to be covered
are provided below:
manual welding per AWS A3.0: Welding with
the torch, gun, or electrode holder held and manipulated
by hand.
semiautomatic welding per AWS A3.0: Manual
welding with equipment that automatically controls one
or more of the welding conditions.
mechanized welding per AWS A3.0: Welding
with equipment that requires manual adjustment of the
equipment controls in response to visual observation of
the welding with the torch held by a mechanical device.
automatic welding: Welding with equipment
that requires only occasional or no observation of the
welding, and no manual adjustment of the equipment
controls.
9.2.1 Equipment Requirements. Manual GTAW
equipment may include all or part of the items listed in
Table 19. After this equipment is assembled and readied
for welding per individual plant standards and equipment
supplier installation and operation manuals, the welder is
ready to begin welding operations.
9.2 Manual and Semiautomatic Welding. Welders
must be comfortable and relaxed before they weld. No
matter what torch manipulation technique is used, the
welder must try to maintain optimum torch and travel angles. By maintaining a slight leading travel angle (forehand technique) and a torch angle perpendicular to the
weld joint, the leading edge of the weld pool can easily
be seen by the welder. This orientation of the welding
torch will minimize undercutting of the base metal.
Manual GTAW is used for the welding work where
complex shapes, limited production runs, difficult to access weld joints or cost of capital equipment preclude the
use of mechanized or automatic GTAW. The manual
GTAW process can be applied to a wide range of products like stairway railings and tubing assemblies for hos-
9.2.2 Manual Welding Operation Techniques.
When manually welding, there are six basic areas that
should be considered by the welder:
(1)
(2)
(3)
(4)
(5)
(6)
9.2.3 Arc Initiation. There are a variety of ways the
welder can initiate an arc. The welder’s choices of arc
initiation techniques will be mostly dictated by what
capabilities are built into the GTAW power source.
71
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Arc initiation
Torch manipulation
Current level control
Workpiece manipulation
Filler metal addition
Extinguishing the arc
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Table 19
Welding Equipment or Components
Equipment/Techniques
Manual
Semiautomatic
Mechanized
Automatic
Power Sources
X
X
X
X
Current Control Mechanism
• remote foot pedal rheostat
• finger control rheostat
• contactor
• programmable weld controller
X
X
X
—
X
X
X
—
X
X
X
X
—
—
X
X
Arc Voltage Control
—
—
X
X
Electrodes
X
X
X
X
Gas Regulators
X
X
X
X
Gas Flowmeters
X
X
X
X
Gas Supply, (shielding, backing, trailing)
X
X
X
X
Gas Hoses (shielding, purging, etc.)
X
X
X
X
Electrical Cables (workpiece lead, etc.)
X
X
X
X
Torch Cooling System
X
X
X
X
Wire Feeder
X
X
X
X
Vision System
—
—
X
X
Seam Tracking Equipment
—
—
X
X
Workpiece Manipulators
• manual
• mechanized
X
X
X
X
X
X
—
X
Safety Equipment (eye protection, etc.)
X
X
X
X
Fume Exhaust Equipment
X
X
X
X
Descriptions of these initiation techniques are provided
below.
IMPORTANT NOTE: Because radiation from a highfrequency generator may disturb radio service, the use of
this type of equipment is governed by regulations of the Federal Communications Commission. The user should follow
the instructions of the manufacturer for the proper installation and use of high-frequency generating equipment. The
high-frequency radiation and conduction can also trigger
electronic alarms and interfere with electronic and computer equipment, heart pacemakers and telephone systems.
9.2.3.1 High Frequency. High-frequency arc starting can be used with DC or AC power sources for both
manual and automatic applications. In manual operations, a foot switch is usually used to initiate the highfrequency unit and to raise or lower the weld current. The
high-frequency generator superimposes a high voltage
upon the welding circuit. The ionized gas will then conduct welding current that initiates the welding arc.
The addition of continuous high-frequency energy on
the AC welding circuit also assists in reestablishing the
arc at points of current reversal, i.e., twice every cycle.
This technique of arc stabilization finds its greatest application in gas tungsten arc welding of aluminum and
magnesium.
9.2.3.2 Touch or Scratch Start. With the power
source energized, the contactor closed, and shielding gas
flowing through the torch, the torch is lowered to the desired welding location until the tungsten electrode makes
contact with the workpiece. The torch is then quickly
withdrawn in a backward motion a short distance, similar
to striking a match, to establish the arc.
72
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
The advantage of this method of arc initiation is its
simplicity of operation for manual welding. The disadvantage of touch starting is the tendency for the electrode
to stick to the workpiece, causing a tungsten inclusion.
To overcome this limitation, an arc initiation coupon or
run-on tab can be used where the arc is initiated on the
tab. The welder then manipulates the weld arc onto the
workpiece.
9.2.4.3 Brace Technique. The brace technique is a
technique used in manual welding of vessels, sheet metal
and structures. In this welding technique, the welder stabilizes the torch by resting his wrist, arm or elbow as far
away from the weld zone as possible and sliding the
wrist in the direction of welding. Figure 65 shows the
wrist-brace technique.
9.2.4.4 Freehand Technique. The freehand technique should be used only when no other technique is
feasible. Most welders are not steady enough to perform
quality welding without some technique to stabilize the
torch. Uncontrolled torch motion can lead to tungsten
contact with the work or filler.
9.2.3.3 Pulse Start/Capacitor Discharge. Application of a high voltage pulse between the tungsten electrode and the work will ionize a path through the
shielding gas, which will enable the weld current to start
flowing. This method is generally used with DC power
sources.
9.2.5 Workpiece Manipulation. During the planning
of the welding operation sequence and qualifying the
welding procedure and welders, the welding engineer
must establish in which welding position the joint will be
welded in production. Many considerations must be
made relative to welding joint position. Can the component be mounted on a positioner? Can the part be lifted
with an overhead crane; or, is the component mounted in
a fixed installation? Once these questions are answered,
the welding procedure that is developed must match how
the component will be manipulated during welding to
maintain the proper joint position.
The highest deposition rates in GTAW can be obtained when welding is conducted in the flat position because gravity keeps the molten metal in the joint.
Welding in the flat position allows for the fastest travel
speeds. The next best is the horizontal position. Due to
these facts, all efforts should be made to orient the weld
joint in either the flat or horizontal position. However, on
some jobs, the workpiece cannot be manipulated and
therefore vertical or overhead welding may be required.
Excluding fixed position welding, there are two basic
ways (manual and mechanical) the welder can manipulate the workpiece to maintain the optimum joint position. Figure 66 shows an example of a workpiece
manipulator used in manual welding.
9.2.4 Torch Manipulation. After the welder has initiated the arc, the torch must now be manipulated to move
the molten weld pool along the welding joint. Depending
upon the joint type, weld position and accessibility to the
weld joint, the welder can employ different torch manipulation techniques. Care should be taken when using any
torch manipulation technique to prevent the tungsten
electrode from contacting the molten pool. If this happens, the arc should be extinguished and the electrode reground. If the weld is to be of radiographic quality then
the tungsten inclusion should be ground out.
9.2.4.1 Walking-The-Cup. Walking-the-cup is a
technique for manipulating the torch when manually
welding groove and fillet welds. With this technique, the
electrode extension is adjusted to allow the proper arc
length while the edge of the cup rests on the side of the
joint. The torch is manipulated in a manner to swing the
tip of the tungsten back and forth across the side of the
joint by “walking-the-cup” on each edge of the joint. The
left or right edge of the gas nozzle/cup is in constant contact with the members giving the cup a walking motion
on the weld joint. One limitation of this technique is that
it is very difficult to walk-the-cup when welding pipe
less than 2 in. [50 mm] in diameter. Figure 62 shows a
photo where the walking-the-cup technique is being
used.
9.2.5.1 Manual Manipulation. For small pipe
welds that can be rotated, it may be economical to make
the welds using pipe rollers, welding the top quarter, then
manually rotating the pipe and completing the weld in
quarters. Other ways the weld joint can be manually positioned are by physically moving the component or
using lifting devices such as overhead cranes or universal
balance positioners that are manually operated.
9.2.4.2 Dragging-The-Finger. Dragging-the-finger
is a technique used in manual welding of all types of
joint configurations. It can be used when welding all
diameters of pipe and tubing. Figure 63 shows draggingthe-finger technique.
In this welding technique, a fingerstall is made by
overlapping a “sleeve” of fiberglass material approximately 8 in. [200 mm] long. The fingerstall, shown in
Figure 64, is placed over the middle finger and should
extend approximately 1 in. [25 mm] beyond the end of
the finger. The fingerstall is used to stabilize the hand
holding the torch as it is slid along during welding.
9.2.5.2 Mechanical Manipulation. Mechanical
manipulation of the workpiece can be done with one or
more motions. An example is rotation about one axis.
This is normally accomplished with turning rolls, head-
73
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 62—Walking-the-Cup Technique
Figure 63—Dragging-the-Finger Technique
74
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 64—Folding Fingerstall Technique
Figure 65—Brace Technique Showing Wrist in Contact
with Workpiece to Stabilize the Torch
75
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
stock and tail stock arrangements, or turntables, all of
which rotate the assembly about a single axis. Axis
motion can be provided by electrically driven gears (see
Figure 67).
9.2.5.3 Rotating and Tilting. Rotating and tilting
is normally accomplished with a positioner that has a tilting table as well as rotation. A third example of positioning is accomplished by adding vertical or linear
movement.
9.2.6 Filler Metal Addition. The majority of joints
that are GTA welded require the addition of filler metal to
eliminate underfill of the joint or to fill up a prepared joint
preparation such as a V-groove. Filler metal comes in a
variety of forms: cut length filler wire, spooled filler wire,
consumable inserts, and integral sockets. Each of these
filler metal forms requires different welder techniques.
When the addition of filler metal is necessary, a forehand technique is used; the filler metal is held about 15°
to the work and about one inch away from the starting
point until the weld pool is formed. When the weld pool
becomes fluid, filler metal is added. The rate of forward
speed and filler metal added will depend upon the desired width and height of the bead. See Figure 65, which
shows a welder adding filler metal.
Figure 66—Small Rotary Positioner
Used for Workpiece Manipulation
Figure 67—Mechanical Manipulation in a Mechanized Welder
76
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
9.2.6.1 Cut Length Filler Wire. When welding
sheet metal, filler material is normally dipped in and out
of the weld pool to control weld size, heat input and weld
bead geometry. When retracting weld filler rod from the
pool, care should be exercised to insure the hot end of the
rod is not removed from within the welding torch’s protective gas envelope. If the end of the filler wire should
become oxidized, then the oxidized end should be cut
prior to using the remaining wire. When welding a root
pass, filler metal is normally held in one position and not
manipulated. When welding filler and cover passes, filler
metal may be manipulated a slight amount based on joint
opening. During welding, the welder must be careful not
to touch the filler wire to the tungsten electrode, since the
electrode would become contaminated.
Prior to using the filler wire, the welder should verify
that the type of the filler wire matches the filler material
specified81 on the welding procedure. Additionally, the
welder should assure cleanliness of the filler material.
Training of the welder is necessary to assure that approved weld wire identification and storage procedures
are followed.
include more consistent weld bead fusion, and smooth,
uniform underbead surfaces. Additionally, the chemical
composition of the consumable insert can be varied to
obtain an optimum weld microstructure. An example of
this would be to vary the composition of the insert for
automatic stainless steel welding so that the proper
amount of delta ferrite would be formed during solidification. Disadvantages include higher cost and quality
control of consumable.
The consumable-insert method of root-pass welding
originally was developed for use in the fabrication of nuclear powered submarines, for which the highest quality
weld joints are essential and where access to a part of a
joint is limited because of the congested environment.
This method is intended primarily for applications in
which:
(1) accessibility is limited to one side of the joint;
(2) smooth, uniform, crevice-free inner weld surface
contours are essential; and
(3) the highest quality attainable in the root pass is
mandatory.
This method involves the use of an insert that is completely fused by a gas tungsten arc. The insert permits the
deposition of a root pass bead that is smooth and uniform
even though welding is done from one side only, such as
in pipe welding. The insert method is especially useful in
butt-welding of pipe, although there are no particular restrictions on its application. However, consumable inserts must be precisely fitted.
9.2.6.2 Spooled Filler Wire. Wire feeders may be
used to add spooled filler metal to the weld joint. By
using this technique, cold wire is fed into the leading
edge of the molten pool while hot wire typically is fed
into the trailing edge. When retracting weld filler rod
from the pool, care should be exercised to insure the hot
end of the rod is not removed from within the welding
torch protective gas envelope. Filler additions may be
continuous or pulsed. By mechanically feeding wire to
the welding operation, the manual operation is now considered a semiautomatic GTAW process. Figure 6882
shows two ways spooled wire can be added during manual welding operations.
As with cut length wire, proper identification procedure and storage requirements must be strictly followed
when using spooled wire. Also, see 5.6.2 related to hot
wire.
9.2.6.4 Pre-machined Integral Filler. A variation
of a consumable insert is a physical feature machined
into one component that will be welded. This feature
provides the filler metal, e.g., fillet welds on socket
joints. The mating component slips inside the socket.
This type of joint design/filler metal addition is used primarily in small diameter, thin walled tubing applications.
Joint tolerances should not allow gaps between the inside
and outside diameters of the mating parts. During fit-up
of socket weld joints, the welder must assure proper
depth of the mating components. This is an autogenous
weld with integral filler metal.
9.2.6.3 Consumable Inserts. Consumable inserts83 are preplaced filler metal that becomes part of the
weld. The consumable insert is fit between the components to be joined prior to welding. Cross sections of
typical insert rings are shown in Figure 69. The welder
must assure that there are no excessive gaps in the joint
after placing the insert into the weld joint. Consumable
inserts provide filler metal additions when welding the
root pass in pipe and other groove joints. Advantages
9.2.7 Autogenous Welds. Autogenous welds are fusion welds made without the addition of filler metal.
Some materials with specific joint geometries such as
square butt, lap and edge type joints may be welded autogenously. The welder needs to maintain close control
of the weld pool to prevent excess penetration, underfill,
and undercut of the weld joint. Joint configurations such
as V-groove butt welds and fillet welds cannot be welded
autogenously since they require the addition of filler
metal to fill the joint.
Metals with thickness up to 1/8 in. [3 mm] can be
welded autogenously. Some materials are not suitable for
81. See Table 20 for examples of AWS specifications related to
GTAW and filler metals.
82. Photos courtesy of CK Systematics.
83. Ref: AWS A5.30-97, Specification for Consumable Inserts.
77
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
(A) SEPARATE GUIDE TUBE WITH CONTROL SWITCH FOR SEPARATE CONTROL OF WIRE FEED
(B) GUIDE TUBE WITH CONTROL SWITCH MOUNTED ON GTAW TORCH
Figure 68—Gas Tungsten Arc Welding Torch with
Wire Feeders [(A) and (B)] for Spooled Wire
being welded autogenously (i.e., without filler metal additions). When filler metal is not added to the weld pool,
the welding engineer must ascertain whether the resultant weld microstructure will be susceptible to hot cracking. Prior to selecting the autogenous welding method,
all parts or assembly requirements should be carefully
checked to ensure that an autogenous weld will meet the
specifications.
9.2.8 Extinguishing the Arc. The previous sections
have briefly described initiating the arc and manipulating
the torch, filler metal and workpiece. Now that the
welder has successfully welded the component, the
welding arc must be extinguished. Care must be taken
when extinguishing the arc to avoid forming crater
cracks and porosity. The welder can achieve this in
several ways.
78
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
CLASS 1—INVERTED T-SHAPED
CL
0.005 in. [0.13 mm] MAX RIB OFFSET
CLASS 2—J-SHAPED
W
W
h2
h1
d1
H
H
d2
h1
h2
d1
IDENTIFICATION
MARKING SHALL BE
ON THIS SURFACE
IDENTIFICATION
MARKING SHALL BE
ON THIS SURFACE
D
D
General Notes:
1. Lands (d1, d2) on either side of the rib shall be on the same plane within 0.005 in. [0.13 mm].
2. Rib surfaces (h1, h2) shall be parallel within 0.002 in. [0.05 mm] and square with lands (d1, d2) within 0.005 in. [0.13 mm].
3. For dimensions and tolerances, see AWS A5.30-97, Table 8.
CLASS 1 AND 2 INSERTS—CROSS-SECTIONAL CONFIGURATION
IDENTIFICATION
1/16 ± 0.002 in.
[1.6 ± 0.05 mm]
STYLE
TYPE
D-8
2
0
S-
M
SCHEDULE
1/8 ± 0.005 in.
[3.2 ± 0.13 mm]
(STYLE E)
I.D.
O.D.
3/16 ± 0.005 in.
[4.8 ± 0.13 mm]
(STYLE D)
CLASS 3—SOLID RING INSERTS—PLAN VIEW AND CROSS-SECTIONAL CONFIGURATION
Figure 69—Cross Sections of Typical Consumable Inserts
After the arc has been extinguished, it is good practice
to flow the shielding gas from the torch over the end of
the weld to permit this area to cool under the protective
gas. At the same time, this allows the tungsten electrode
to cool under the shielding gas and prevents its oxidation. The filler material end should be maintained under
the shielding gas to prevent oxidation.
effective methods for extinguishing the arc. In this
method, the size of the weld pool is decreased by decreasing the current with a foot or hand controlled rheostat.
9.2.8.2 Weld Tie-In. Moving the arc up and over
to the side of the joint (while remaining in the joint) or
over the previous pass or back stepping is effective in
minimizing disturbance of the final weld pool. A gradual
breaking of the arc will reduce the possibility of porosity
and crater cracks.
9.2.8.1 Decreasing the Current (Down Slope,
Down Ramp). Decreasing the current is one of the most
79
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
IDENTIFICATION MARKING SHALL
BE ON THIS SURFACE
37-1/2˚± 2-1/2˚
D
C
L
(e)
(f )
NOTE (1)
H
(d)
H/2
(a)
(c)
W
(b)
General Notes:
• For dimensions and tolerances, see AWS A5.30-97, Table 8.
• When specified, rings 1-1/2 in.–2 in. [38 mm–509 mm] in diameter shall be formed of 5/32 in. [4 mm] material.
Note:
1. Reference diameter for correlating with pipe I.D.
CLASS 4 INSERTS—CROSS-SECTIONAL CONFIGURATION
WIDEST PORTION
OF INSERT
W
H
1/8 in. x 5/32 in. [3.2 mm x 4.0 mm]
WITH SLIGHT RADIUS ON EDGES
308
R
CLASS 5 INSERTS—CROSS-SECTIONAL CONFIGURATION
Figure 69 (Continued)—Cross Sections of Typical Consumable Inserts
9.2.8.3 Filling the Crater. In this method a small
quantity of filler metal is added just as the electrode is
being withdrawn. This will compensate for the solidification shrinkage of the weld pool and provide a little
extra filler material to help prevent a shrinkage cavity.
After welding is complete, the welder should visually
inspect the welds for undercut, underfill, excess penetration or reinforcement, crater cracks, and surface porosity.
These conditions should be reworked according to ap-
proved shop procedures prior to releasing the component
to final inspection. This part of the welding operation is
also applicable to mechanized and automatic welding
techniques.
9.3 Mechanized Welding. Mechanized welding is used
for large production run applications where there is good
welding joint accessibility and where consistent joint fitup can be maintained. Additionally, mechanized welding
80
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
is used when quality requirements are more critical. Partto-part consistency is significantly more important for
mechanized welding as compared to manual welding.
Planning for manufacturing components that will be
welded with mechanized GTAW techniques begins
when the component is being designed. Joint access must
be provided for the welding head (torch holder) and the
wire feed guide tube (if used). Fixturing concepts need to
be established to assure proper joint fit-up and that dimensions are maintained after welding. Fixturing for
mechanized welding is generally more complex than the
fixtures used during manual welding. Considerations
need to be made for how filler material will be added and
whether trailing gas shields are required.
Mechanized GTAW can be used to weld a variety of
joint geometries and part configurations. The basic
equipment requirements to perform mechanized GTAW
are shown in Table 19. There are many different types of
equipment variations for mechanized welding that range
from lathe-type welding set-ups (see Figure 70) to large
gantry type welding systems (see Figure 67). In these
examples, a mechanical device holds the welding head
and the operator can make manual adjustments to the
equipment controls to vary travel speed, welding current,
or torch position.
9.3.1 Equipment Requirements. Mechanized
GTAW equipment may include all or part of the items
listed in Table 19. After this equipment is assembled and
readied for welding per individual plant standards and
equipment supplier installation and operation manuals,
the welder or welding operator is ready to begin welding
operations.
9.3.2 Circumferential Mechanized Welding. A typical circumferential welding operation using mechanized
GTAW equipment would have an operation sequence
Figure 70—Lathe-Type Welding Setup
81
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
similar to manual welding, except that the torch position
(side-to-side placement relative to the joint) would be
controlled manually. The welding operation would still
include arc initiation, torch manipulation, filler metal addition, workpiece manipulation and extinguishing the arc
as basics to the operation. Figure 67 shows a mechanized
circumferential welding operation.
Prior to initiating the welding cycle or weld controller,
the welding operator sets the RPM of the headstock to
the proper setting so that the travel speed of the workpiece relative to the stationary torch will match the speed
specified in the welding procedure. The welding operator
can check the workpiece travel speed by simply timing
how long it takes the workpiece to make one revolution.
Travel speed is then determined by dividing the circumference of the workpiece by the time required to complete one revolution. On more complex systems the
workpiece positioner can have a tachometer that controls
the RPM of the positioner. The welding travel speed and
part diameter are entered into the weld controller, and the
computer control calculates and controls the positioner’s
rotational speed.
9.3.2.1 Arc Initiation. Mechanized welding employs the same variety of arc initiation techniques as offered by manual welding, except that touch (scratch)
starting is rarely used. These techniques were discussed
previously in Section 5.
When an automatic voltage control (AVC) system is
used in conjunction with mechanized welding, the weld
torch is positioned over the weld joint and the AVC unit
is instructed to set the initial arc gap. This is accomplished by the AVC head slowly lowering the welding
torch towards the workpiece until the tungsten electrode
contacts the workpiece. An electrical circuit is made
when the AVC system senses the contact between the
electrode and the workpiece. Once the circuit is made,
the AVC head retracts the welding torch a preset distance. Once the arc gap position is set, the AVC unit signals the weld controller and the arc initiation cycle is
started. During the welding operation, the AVC monitors
the arc voltage to maintain a constant electrode tip to
workpiece distance. If the AVC unit detects a change in
voltage, the AVC unit promptly adjusts the height of the
welding torch so that the programmed arc gap can be
maintained.
9.3.3 Filler Metal Addition. During mechanized
welding, filler metal is typically added in three different
ways. The first way is the use of spooled wire (cold or
hot), which is added by a mechanical wire feeder where
the wire speed is controlled by a programmable weld
controller or an independent speed controller. The wire
may be continuously fed at a constant speed, pulsed at a
programmed feed rate, or mechanically dipped into and
out of the pool. In an example of this method, an eccentric device rotates and causes the filler metal guide tube
to be pulled and pushed, thus causing the constantly fed
filler metal to be dipped into and out of the weld puddle.
This action simulates how a welder would manually feed
filler metal into the weld puddle. With the advances in
computer controls, the weld controller can now be programmed to electrically control the wire feeder to pulse
feed the wire into the weld puddle, thus simulating the
manual process of adding filler metal to the weld puddle.
The second and third ways filler metal can be added
during mechanized welding are by using a consumable
insert or as an integral socket. Requirements and descriptions of these filler metal addition techniques were previously described in 9.2.6.3 and 9.2.6.4. There is no
difference between the use of inserts or sockets between
manual and mechanized welding except that fit-up becomes even more critical for mechanized welding. High
deposition rates can be achieved with the use of hot wire
feed techniques.
9.3.2.2 Torch Manipulation. Now that the welding operation is progressing, the welding operator may
monitor the position of the tungsten electrode relative to
the welding joint centerline. The operator must adjust the
position of the weld pool to assure complete fusion of the
joint sidewalls. This is accomplished by manually adjusting the welding head cross slide so that the arc is centered over the joint. Welding current can either be
controlled manually or by a programmable weld logic
controller. If the weld logic controller were used, the
welding current, pulse frequency and voltage would be
programmed prior to starting the welding operation.
9.3.2.3 Current Control. Additionally, the current
ramp-up and slope-down cycles can also be programmed. If the welder manually adjusts the current
level, a foot or hand controlled rheostat would be used to
vary the current level during current ramp-up and down.
The current can also be manually controlled during welding, to maintain a constant bead width and penetration
profile.
9.3.4 Extinguishing the Arc. After the weld is completely made around the part’s circumference, the arc
must be extinguished. As with manual welding there are
a variety of techniques like current down slope and weld
overlap that can be used. The current down slope technique can either be controlled manually or by the programmable weld logic controller. The initiation of the
current down slope by the programmable weld logic controller can be initiated manually (welding operator
pushes end of weld cycle button on control console), or
9.3.2.4 Workpiece Manipulation. After the arc is
initiated, the welder starts the workpiece manipulator.
82
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
automatically initiated by a position feedback device located on the headstock positioner. An encoder or resolver
feedback device that is mounted to the positioner’s drive
motor or rotational axis can send a signal to the weld
logic controller when the component has passed through
360° of rotation. Once this position signal is received, the
weld logic controller initiates the current down slope
cycle and stops the positioner’s motion. After the arc is
extinguished, the shielding gas continues to flow for a
preset amount of time. This protects the weld crater from
excessive oxidation.
This is just one example of a mechanized welding operation. As this example illustrates, the complexity of the
system can vary from almost all manually controlled
welding parameters to almost a completely automatic
welding system. When assessing welding needs, many
decisions need to be made. The foremost question that
needs to be answered is “What GTAW technique produces the part for the lowest cost yet still meets the fitness for purpose?” Assuming that the cost of the capital
equipment can be justified and that consistent, highquality welds are required the next technique that could
be considered is automatic GTAW.
merged arc welding (SAW). Like the other arc processes,
heat input to the weldment is fairly high, resulting in reduced mechanical properties and increased weldment
distortion. Perhaps the most restrictive factor is the large
number of welding variables that must be controlled. In
addition to welding current, travel speed, electrode position, and wire feed speed, arc manipulators (hard automation) or robots (flexible automation) must be designed
to meet these additional requirements, and this complexity adds to the cost of the system.
Where weld quality requirements are high, when the
materials cannot be joined by any other process or when
production quantities are large, automation of the GTAW
process can save considerable time and money. The key
to a successful automatic welding operation is to get consistent joint fit-up in the first place and make sure that the
joint is located consistently from part to part.
9.4.1 Orbital Welding. In selecting orbital welding
applications, many considerations should be made. A
few of the key questions that should be answered are:
(1) What size (outside diameter)/wall thickness will
be welded?
(2) What kind of welding head will access the joints?
(3) What kind of joint fit-up does the joint preparation
process yield? Does it need to be improved?
A thorough evaluation of the equipment and installation needs should be conducted prior to selecting the
equipment. Once the process selection work is completed, a welding parameter development program
should be run to determine the relationships between the
key welding parameters. Parameters that need to be controlled are: current levels (if pulsed current is used, high
and low values need to be established), travel speed,
pulse frequency, shielding gas type, backside shielding
pressure, electrode diameter, and tip preparation. Also,
work should be completed to define joint fit-up requirements and what the joint preparation geometry should
be. Also, if filler metal is to be used in the form of inserts
or integral sockets, or if the weld is to be made autogenously, evaluations should be performed to determine the
metallurgical structure of the resultant weld. Once this
work is complete and the welding operators are trained,
production can be initiated.
9.4 Automated Welding. Manual GTAW is a laborintensive process that places great demands on operator
skill levels. Automation can reduce level of skill required
of the operator, thus reducing direct labor costs. Automation places fewer physical demands upon the operator,
resulting in increased arc on time and higher deposition
rates. The basic equipment requirements to perform
automated GTAW are shown in Table 19.
Quality improvements can be realized through automation because of the greater consistency of electrode
and filler wire placement and the greater level of control
possible over the welding parameters. Automation can
also overcome problems associated with synchronizing
filler wire movement, travel speed, and arc current at the
start and end of the weld.
As with any of the other welding processes, the decision to automate GTAW should be preceded by a careful
analysis of production volume, floor space, inventory,
manpower, and investment requirements. Thought
should also be given to changes in product design, tolerances and fit-up, processing and scheduling, and fixturing that might simplify the design of the automatic
welding station.
After concluding that automation is feasible, consideration should be given to the selection of the welding
process itself. GTAW produces very high weld quality
and can be used with a broad array of metals, but there
are several disadvantages as well. The GTAW process
has an inherently low deposition rate when compared to
processes like gas metal arc welding (GMAW) and sub-
9.4.1.1 Arc Initiation. Arc initiation is controlled
by the orbital weld controller. The arc can be initiated
with high-frequency or capacitance discharge. Details of
arc initiation are provided in Section 5.
9.4.1.2 Torch Manipulation. In orbital welding,
the welding head is clamped rigidly over the tubing or
pipe to be welded. The tungsten electrode is centered
over the welding joint and the tungsten to workpiece distance (arc gap) is preset. The tungsten electrode is then
83
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
dinally or laterally over the weld pool without moving
the welding electrode. These oscillators consist of electromagnets, located close to the arc, that are powered by
a variable-polarity, variable-amplitude power supply.
Control features include adjustable oscillation frequency
and amplitude, and separately adjustable dwell times.
Seam trackers are used to maintain the position of the
arc over the weld joint centerline. Seam tracking equipment can be mechanical probes, through-the-arc or vision based. Each type of tracking equipment has its own
idiosyncrasies. Mechanical probes physically track the
joint. Through-the-arc trackers rely on the welding head
to be moved back and forth across the joint (weave pattern) as the weld progresses linearly. Arc voltage readings are taken at the peak amplitude of the weave pattern,
which occurs on each side of the weld joint. A joint sidewall is needed so that values of voltage can be compared
to determine if the arc is centered between the sidewalls.
This requirement limits the application of the throughthe-arc seam tracking to joints with preparations, like Vpreps, that are deeper than 3/8 in. [10 mm]. If the system
detects a difference in voltage from sidewall to sidewall,
the torch is moved by a mechanized cross slide back towards the center of the joint so that successive voltage
readings will be the same at each joint sidewall. The rate
of correction is dependent upon the sensitivity and gain
settings that were initially programmed into the weld
logic controller.
As can be seen from the previous paragraphs, there
can be an increasing complexity added to the torch manipulation capabilities of the system.
Figure 71—Orbital GTAW Weld Head
rotated around the part. Figure 7184 shows an orbital
tube-welding head. A gear driven drive train moves a
guided slip sleeve. The guided sleeve, which holds the
tungsten electrode, is located inside the welding head.
The welding current and shielding gas are fed through an
umbilical cable that also contains a drive motor control
cable. The travel speed of the electrode is controlled by
the orbital welding controller.
In some large diameter welding applications, special
equipment like arc oscillators and seam trackers can be
added to assist with torch manipulation. Arc oscillators
are used to change the location of the welding puddle
with respect to the original weld path. This may be accomplished mechanically or electromagnetically.
The width of gas tungsten arc welds can be increased
by mechanical oscillation. Mechanical arc oscillation can
be achieved by mounting a GTAW torch on a cross slide
that provides movement of the torch transverse to the
line of travel. Such equipment provides adjustable crossfeed speed, amplitude of oscillation, and dwell on each
side of the oscillation cycle.
Better fusion of joint sidewalls and a reduction of the
disruptive effects of arc blow can be obtained by magnetic oscillation. Such oscillators deflect the arc longitu-
9.4.1.3 Workpiece Manipulation. In orbital welding, the workpiece is fixed and the electrode is rotated
around the joint by the welding head. Therefore, during
welding, workpiece manipulation is not required.
9.4.1.4 Filler Metal Addition. When orbital welding is conducted, filler metal may or may not be added.
Like in mechanized welding, filler metal may be added
using spooled wire or consumable inserts into the joint.
An example of spooled wire feed is shown in Figure
22.85 The use of consumable inserts also serves to help
alignment of the weld joint. Descriptions of these filler
metal types are found in 9.2.6.
9.4.1.5 Extinguishing the Arc. After the weld is
completed, the arc can be extinguished by ramping down
the current and/or by the weld overlap technique. The current ramp down schedule is executed at a preprogrammed
time after the electrode has completed its travel around
85. Emerson, John. 1999. “Multipass Orbital Welding of Pipe.”
The Tube and Pipe Journal, Vol. 10, No. 1, January/February
1999, pp. 22–26.
84. Photo courtesy of Swagelok Co.
84
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
the weld joint. Likewise, the amount of weld overlap is
preprogrammed and the amount of overlap at the weld’s
completion is controlled by the weld controller.
10.3.1 Edge Preparation. The weld joint design determines the type of edge preparation that is required for
gas tungsten arc welding. Depending on the thickness of
the weld joint, several configurations for joint cross
sections can be selected. For thicker section weld joints,
a U-groove, J-groove, or V-groove weld joint edge preparation may be desired to ensure complete weld penetration (see Figure 73). For thinner section weld joints,
usually under 0.10 in. [2.5 mm] in thickness, a squaregroove edge preparation will usually be sufficient for
maintaining complete weld penetration during welding.
Joint preparations which are often used for GTAW
are the J-groove or U-groove. These are often used for
precision mechanical or closely fitted components (either
thin or thick). Figure 73 shows some examples of these
types of preparations.
Figure 69 shows consumable inserts in U-grooves.
Consumable inserts with GTAW are more often used
with an open root U-groove.
Mechanical means of weld joint edge preparation are
usually the most desirable, but it is not always the most
cost effective means of removing surface oxides or contaminants. Certain mechanical edge preparation techniques will produce consistent weld joint edges to
minimize weld joint gaps and mismatch when assembling part details. In all mechanical methods, it is important to maintain sharp machining or cutting tools to avoid
working (smearing) or overheating of the weld joint
surfaces.
10. Joint Design, Preparation, and
Welding Positions
10.1 Introduction. Welded joints are designed primarily
to meet strength and safety requirements for the service
conditions of the welded component. Consideration must
be given to the manner in which the stress will be applied
in service, whether the joint will be in tension, compression, shear, bending or torsion, and whether the joint is
statically or dynamically loaded. Fatigue must be factored into joint design for dynamically loaded applications. Joints should be designed to avoid stress-risers and
to reduce residual stress.
A primary consideration in preparing the joint design
is the provision for proper accessibility. Any joint opening should be adequate to permit the arc, shielding gas
and filler metal to reach the bottom of the joint. Other
factors affecting joint design include base metal (such as
surface tension, fluidity, melting temperature, etc.), metal
thickness, whether filler metal is to be added, weld penetration requirements, joint restraint, and joint efficiency
requirements. Joint efficiency86 is defined as the ratio of
the joint strength to the base metal strength and is generally expressed as a percentage.
10.2 Basic Joint Configurations and Welding Positions. The five (5) basic joints are butt, corner, T-joint,
lap, and edge; these are shown in Figure 72.87 Many variations are derived from these basic joints. In all instances
the primary objective is to maintain the desired weld
quality and to minimize welding costs.
Factors affecting cost are part preparation, setup or
fixturing, and actual welding. Welding position refers to
the overall orientation of the weld axis and workpieces.
The welding positions, with variations, are flat, horizontal, vertical and overhead. Refer to AWS A 3.0, Standard
Welding Terms and Definitions, for more detailed information pertaining to weld joints and welding positions.
All joint configurations and positions can be welded
using the GTAW process.
10.3.2 Surface Cleaning. Whichever edge preparation is selected, prior to welding, the weld joint edges and
adjacent areas (on and out of the heat-affected zone)
should be wiped with a clean lint free cloth moistened
with an approved solvent such as alcohol, acetone, or methyl ethyl ketone (MEK), depending on the material type,
to ensure cleanliness during welding. Cleanliness of both
the weld joint area and the filler metal are important considerations when welding with the GTAW process. Edge
preparation tools can be a source of contaminants. Oil,
grease, shop dirt, paint, marking crayon, rust or corrosion
deposits, and moisture must all be removed from the joint
edges and metal surfaces to a distance beyond the heataffected zone; typically 1/2 in. [13 mm] is sufficient.
10.3 Edge Preparation and Surface Cleaning. Edge
preparation and surface cleaning are an integral part of
weld joint design and quality. Surface cleanliness is important regardless of joint design.
11. Welding Characteristics of
Selected Alloys
11.1 Introduction. Most metals can be welded by the
GTAW process. Some metals (e.g., titanium and other reactive metals) are particularly suited to the GTAW process because these can be welded in an inert gas chamber
or with very good shielding to provide sufficient protection from contamination by the atmosphere. Metals and
86. Joint Efficiency (%) = (Weld Joint Strength/Base Metal
Strength) x 100.
87. Source: AWS 3.0:2001, Standard Welding Terms and Definitions, Figure 1.
85
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
APPLICABLE WELDS
BEVEL-GROOVE
FLARE-BEVEL-GROOVE
FLARE-V-GROOVE
J-GROOVE
SQUARE GROOVE
U-GROOVE
V-GROOVE
BRAZE
(A) BUTT JOINT
APPLICABLE WELDS
FILLET
BEVEL-GROOVE
FLARE-BEVEL-GROOVE
FLARE-V-GROOVE
J-GROOVE
SQUARE-GROOVE
U-GROOVE
V-GROOVE
PLUG
SLOT
SPOT
SEAM
PROJECTION
BRAZE
(B) CORNER JOINT
APPLICABLE WELDS
FILLET
BEVEL-GROOVE
FLARE-BEVEL-GROOVE
J-GROOVE
SQUARE-GROOVE
PLUG
SLOT
SPOT
SEAM
PROJECTION
BRAZE
(C) T-JOINT
APPLICABLE WELDS
FILLET
BEVEL-GROOVE
FLARE-BEVEL-GROOVE
J-GROOVE
PLUG
SLOT
SPOT
SEAM
PROJECTION
BRAZE
(D) LAP JOINT
APPLICABLE WELDS
BEVEL-GROOVE
FLARE-BEVEL-GROOVE
FLARE-V-GROOVE
J-GROOVE
SQUARE-GROOVE
U-GROOVE
(E) EDGE JOINT
Figure 72—Basic Joint Types
86
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
V-GROOVE
EDGE
SEAM
SPOT
PROJECTION
BRAZE
AWS C5.5/C5.5M:2003
Figure 73—Weld Joint Edge Preparation
(U-Groove, J-Groove, and V-Groove)
87
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
alloys that vaporize very readily when liquefied are not
recommended for GTAW. Such metals include cadmium,
zinc and those alloys (e.g., silver brazing filler metals
and brasses) which contain high percentages of these low
melting point metals. Not only does the tungsten electrode become quickly contaminated and the arc become
unstable, there can be a potential health hazard.
Details on the welding procedures for specific metals
and alloys, including suggested preweld and postweld
heat treatments and recommended filler metals, are beyond the scope of this publication. Data on specific metals and alloys can be found in the AWS Welding
Handbook, 8th Edition, Vol. 3; ASM Handbook, Vol. 6,
“Welding, Brazing, and Soldering,” 1993, ASM International; and “Welding Metallurgy,” G. E. Linnert, 1994,
AWS. AWS specifications for filler metals suitable for
GTAW are listed in Table 20. In general, when it is recommended that an alloy be in a specified heat treated
condition prior to welding, that a given preheat and post
heat be applied, and/or that the filler material provides a
given chemical composition, then these recommendations are valid for any welding process, including GTAW.
This section presents information on metallurgical
considerations and potential problems unique to the
GTAW process. For the common alloys, Table 8 provides
suggested types of welding current, electrode compositions, and shielding gas compositions for optimum weld
quality. The principal effects of shielding gas and electrode geometry on welding parameters were discussed in
Sections 4, 6, and 7. The general effect is that as one goes
Table 20
AWS Specifications Related to Gas Tungsten Arc Welding(1)
Specification Number
Title
A5.7
Specification for Copper and Copper Alloy Bare Welding Rods and Electrodes
A5.9
Specification for Bare Stainless Steel Welding Electrodes and Rods
A5.10/A5.10M
Specification for Bare Aluminum and Aluminum Alloy Welding Electrodes and Rods
A5.12/A5.12M
Specification for Tungsten and Tungsten Alloy Electrodes for Arc Welding and Cutting
A5.13
Specification for Surfacing Welding Electrodes for Shielded Metal Arc Welding
A5.14/A5.14M
Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods
A5.15
Specification for Welding Electrodes and Rods for Cast Iron
A5.16
Specification for Titanium and Titanium Alloy Welding Electrodes and Rods
A5.18/A5.18M
Specification for Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding
A5.19
Specification for Magnesium-Alloy Welding Electrodes and Rods
A5.21(2),(3)
Specification for Bare Electrodes and Rods for Surfacing.
A5.22(3)
Specification for Stainless Steel Electrodes for Flux Cored Arc Welding and Stainless Steel Flux Cored
Rods for Gas Tungsten Arc Welding.
A5.24
Specification for Zirconium and Zirconium Alloy Welding Electrodes and Rods
A5.28
Specification for Low Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding
A5.30
Specification for Consumable Inserts
A5.32/A5.32M
Specification for Welding Shielding Gases
Notes:
(1) While a seemingly successful GTAW can be accomplished using bare wire or rod of the same alloy as the base metal, this is not recommended.
Chemical composition of filler metals is often adjusted to insure that the weld has the same strength and corrosion resistance as the base metal.
Deoxidizers may also be added to the filler metal to insure a high quality weldment.
(2) Bare rods for GTAW hardfacing have been reclassified in AWS 5.21. See the latest editions of AWS 5.13 and AWS 5.21.
(3) These specifications also include some composite rod classifications for welding with GTAW.
88
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
from 100% argon to 100% helium, the penetration increases. As the included tip angle decreases to a sharper
point, the penetration decreases. These general effects
occur regardless of the base metal. However, the magnitude of the effect will vary, primarily depending upon
the thermal conductivity of the base metal. For example,
it is easier to obtain deep penetration and a narrow bead
with titanium, which has a very low thermal conductivity, than it is with copper, which has a very high thermal
conductivity.
metals (e.g., Type 347). The 300 series filler metals (e.g.,
308, 309) are often used on other base metals (e.g., 410
stainless steel) when postweld heat treatment cannot be
performed.
Argon is recommended for manual welding of thickness up to approximately 1/2 in. [13 mm] because it provides better control of the molten weld pool. For thick
sections, and for many mechanized and automatic applications, argon-helium mixtures or pure helium are often
used to obtain increased weld penetration. Argonhydrogen mixtures are used for some austenitic stainless
steel welding applications to improve bead shape and
wetability. The use of argon-hydrogen mixtures, generally used only on thin gauge 300 series stainless, is not
recommended for other applications without an in-depth
investigation. Mixtures of 98% argon 2% nitrogen have
been reported to be successfully used in the welding of
duplex (50%–60% austenite, 40%–50% ferrite) stainless
steels. Most stainless steels are welded with DCEN.
In general, the precipitation hardening stainless steels
and iron-based superalloys have a liquid weld pool that is
more difficult to control than the weld pool for 300 series
alloys. These alloys have additions of hardening elements (such as Al, Ta, Cu, and Ti) which change the
surface tension of the liquid pool.
Another element that is known to have a strong effect
upon surface tension is sulfur. Figures 74(A) and (B) illustrate the effect of this element on two austenitic stainless steels.88 The shallow penetration produced with
sulfur contents less than 50 ppm can have significant implications for autogenous welds. With very low sulfur
contents (<~50 ppm or 0.005%), the molten weld pool
flows outwards along the top surface away from the center towards the sides. Thus, a shallow and wide weld
bead is created. With high sulfur contents (>50 ppm) the
weld pool flows inward along the top surface toward the
center, and then down at the center. This produces a deep
and narrow weld bead. Some material specifications for
stainless steel now call for 50 ppm–170 ppm sulfur.89
Problems with welding of stainless steels include hot
cracking, which is caused by the metal composition and
the related tensile stress. The 300 series stainless steels
can have hot cracking if the ferrite (or chromium and
nickel) content are not controlled. The hardening elements in the precipitation hardening stainless steels and
superalloys can cause hot cracking. Welding of the freemachining stainless steels, which contain sulfur and
11.2 Carbon and Alloy Steels. Although carbon and
alloy steels are readily welded with the GTAW process,
typical applications involve root pass welding with
GTAW followed by fill passes with SMAW or GMAW.
GTAW is a low deposition rate process, and thus is not
used as much for carbon and alloy steels as are SMAW,
SAW, GMAW or flux-cored arc welding (FCAW). Furthermore, although GTAW provides good shielding and
protection of the weld pool from atmospheric contamination, it does not utilize a flux so it cannot remove or tie
up the impurities, which are present in some steels. An
example of this is the porosity developed by the presence
of impurities in rimmed steels.
Argon or argon-helium shielding gas mixtures are
recommended for welding of carbon and low alloy steels.
Argon is generally used for welding thickness up to
1/2 in. [13 mm], because the molten weld pool under
argon is easier to control than with helium. Helium and
argon-helium mixtures provide deeper penetration for the
same welding parameters. Consequently, these gases are
more commonly used for thicker sections. Argonhydrogen mixtures are not used for steels because of the
potential for hydrogen-induced cracking. DCEN is used
for GTAW of steels.
11.3 Stainless Steels and Iron-Based Superalloys.
Stainless steels of all types (200 and 300 series or austenitic, 400 series of the martensitic and ferritic types, and
duplex and precipitation hardenable) and the iron-based
heat-resistant superalloys, such as A286, are extensively
welded with the GTAW process because they are adequately protected from the atmosphere by the inert gas
shielding. Figure 40 shows the progressive oxidation that
occurs if the inert gas becomes contaminated with oxygen. Similar effects occur if the weld is not adequately
protected.
Filler metal composition is typically close to or nearly
identical to the base metal composition since the filler
metal melts into the weld pool but does not pass through
the arc, where loss of elements can occur. Type 304 base
metal (18-20 Cr, 8-10 Ni) is normally welded using Type
308 filler (19-21 Cr, 10-12 Ni) because there may be
some slight loss of elements in the arc. However, matching filler metal is often used for some stainless steel base
88. Burgardt, P. and Campbell, R., 1992, Chemistry Effects on
Stainless Steel Weld Penetration, Ferrous Alloy Weldments,
Trans Tech Publications, Switzerland.
89. ASTM A270-95a, Standard Specification for Seamless and
Welded Austenitic Stainless Steel Sanitary Tubing, Supplementary
Requirements for Pharmaceutical Tubing.
89
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
(A) 304L STAINLESS STEEL CONTAINING 0.003% (30 ppm) SULFUR, ORIGINAL SCALE 16X
(B) 304L STAINLESS STEEL CONTAINING 0.016% (160 ppm) SULFUR, ORIGINAL SCALE 16X
Figure 74—Effects of Sulfur Content on Bead-on-Plate Weld Bead Shape
in 304L Made with the Same Parameters
255 duplex stainless steel and E-Brite®91 26-1 ultra-high
purity ferritic stainless steel.92
phosphorus (which improve machinability), can also
cause hot cracking. The martensitic stainless steels typically require preheat or postweld heat treatment to avoid
cold cracking.
Gas purity, as discussed in Section 7, is an important
variable and can have a significant effect on the weld and
weldment properties. For example, it has been shown
that the purification of argon shielding gas and backing
gas improves Charpy impact toughness of Ferralium®90
11.4 Aluminum Alloys. GTAW is ideally suited for
welding of aluminum alloys. Welding may be performed
91. E-Brite is a registered trademark of Allegheny Ludium
Corporation.
92. Krysiak, K. F. and Bhadha, P. M., 1990. Shielding Gas
Purification Improves Weld Quality. Welding Journal, Vol. 69,
No. 11, Nov. 1990, pp. 47–49.
90. Ferralium is a registered trademark of Langley Alloys Ltd.
90
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
DIRECT CURRENT, STRAIGHT-POLARITY
(DCEN) PULSED CURRENT
WIRE BRUSHED TO CLEAN SURFACE
Figure 75—GTAW in 6061-0 Aluminum Showing the Surface Contours
with Pulsed Direct Current Straight Polarity (DCEN)
without filler metal for many alloys, however, some alloys weld better with use of a filler metal. The reason for
this is that these alloys, such as 6061, have a composition
that has a tendency for cracking (see Figure 75). Adding
certain filler metals alters the weld metal chemical composition, which minimizes the tendency for cracking
(Type 4043 filler produces less cracking than Type 5356
filler).
Aluminum alloys form refractory surface oxides,
which make joining more difficult. For this reason, most
welding of aluminum is performed with AC (alternating
current using high-frequency arc stabilization) because it
provides the surface cleaning action of DCEP along with
the deeper penetration characteristics of DCEN. Variable
Polarity (VP) or pulsed DC welding is also very successful in welding aluminum. DCEP is sometimes used for
welding thin aluminum sections. DCEN can be used for
high-current automatic welding of sections over 1/4 in.
[6 mm] thick, but since DCEN produces no cleaning action, the aluminum parts must be thoroughly cleaned immediately prior to welding. Porosity is a major concern
with welding of aluminum, especially with DCEN.
Argon shielding gas is generally used for welding of
all thicknesses of aluminum with AC because it provides
better arc starting, greater cleaning action and superior
weld quality than helium. However, when DCEN or
DCEP are used, helium gas provides faster travel speeds
and deeper penetration. Hydrogen is not recommended
for use with aluminum alloys since excessive porosity
can be created. Preheating of aluminum is often required
because of its high thermal conductivity.
gas until it has solidified (magnesium will only burn if it
is in finely divided form).
Magnesium alloys are normally welded with a filler
metal of similar composition. However, occasionally it is
desirable to use a filler metal with a lower melting range
to minimize the possibility of cracking due to thermal
stress created in part by magnesium’s high coefficient of
thermal expansion. An example is the use of AZ91
(875°F–1105°F [468°C–596°C] melting range) filler
with AZ31 (1120°F–1170°F [604°C–632°C] melting
range) base metal.
11.6 Beryllium. Beryllium is a light metal and is difficult to weld because of a tendency toward hot cracking
and embrittlement. GTAW of beryllium is usually performed in an inert atmosphere chamber using argonhelium shielding gas. (Beryllium fumes are toxic—see
Section 15 and ANSI Z49.1 for information on health
and safety issues on welding of beryllium.) Alloys with
low concentrations of beryllium, such as beryllium copper alloys (<2% Be), are truly copper alloys and can be
welded with normal inert gas shielding. On the other
hand, the aluminum beryllium alloys contain large quantities (30%–70%) of beryllium and must be handled as if
they were pure beryllium.
11.7 Copper Alloys. One of the properties of copper alloys is their very high thermal conductivity. GTAW is
well suited for welding of these alloys because the intense heat generated by the arc can produce melting
without a great deal of heat being conducted away from
the weld. However, thick sections frequently need to be
preheated to insure adequate fusion, particularly at the
root of the weld. Most copper alloys are welded with
DCEN and helium because this provides a higher heat
input than argon and allows the heat to stay in the weld
area. AC and VP are sometimes used to weld beryllium
copper and aluminum bronzes because they help break
up the surface oxides that are present. Porosity can be a
big problem with copper alloys. A number of copper
11.5 Magnesium Alloys. Magnesium alloys form refractory surface oxides similar to aluminum alloys, and the
welding considerations discussed in 11.4 apply to these
alloys as well. Welding of most magnesium is done with
AC because of the oxide cleaning action it provides.
There is no fire hazard in welding magnesium provided
the molten weld pool is adequately shielded with inert
91
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
alloys contain high percentages of zinc and lead, which
can create serious welding problems in the form of electrode contamination, welder visibility, porosity, as well
as safety concerns (see Section 15 and ANSI Z49.1).
input, while providing the best inert gas shielding of any
arc welding process. Welding these metals is typically
performed in purged chambers, such as glove boxes (see
Figure 78), containing high-purity inert gases. However,
GTAW is often performed without special purge chambers, by providing the necessary inert gas atmosphere
with special torches that have trailing cups and backup
shielding. To check the effectiveness of the purge chamber or of a shielding method such as a trailing cup, a spot
weld check can be used. Figures 39 and 79 show the criteria used by different companies to verify the effectiveness of a purge chamber prior to doing any GTAW on
titanium alloys. Argon is most frequently used for shielding, because it has higher purity than helium, but helium
and mixtures of the two gases can be used. Argon flow
rates of 15 ft3/hr [7 L/min] or helium flow rates of 40 ft3/
hr [19 L/min] are normally sufficient, even with the large
diameter gas nozzles which are recommended.
11.8 Nickel Alloys. Nickel alloys are often gas tungsten
arc welded, typically with filler metal additions. DCEN
is recommended for all applications and thicknesses, but
AC with high-frequency stabilization may be used for
machine welding. Argon, helium and argon-helium mixtures are the most common shielding gases. Argon with
small amounts of hydrogen (up to 7.5%) is sometimes
used because it provides improved penetration, better
wetability, and provides a reducing atmosphere to remove some impurities. Nickel alloys can exhibit similar
variable weld penetration caused by differences in surface active elements, such as sulfur, as described in 11.3.
In general, nickel alloys (e.g., Inconel®, Monel®,
Hastelloy®93) weld similarly to the 300 series stainless
steels (see Figure 76). However, the weld pool is much
more sluggish and does not flow very well. Weld joints
are often wider on nickel alloys to allow proper wetting.
Nickel alloys also form more slag than stainless steels.
The precipitation-hardening nickel alloys have welding
characteristics similar to the precipitation-hardening
stainless steels. The alloying elements (titanium, copper,
aluminum, and niobium) tend to cause hot cracking.
11.11 Cast Irons. Cast irons can be welded with the
GTAW process because dilution of the base metal can be
minimized with independent control of heat input and
filler metal additions. A high level of welder skill is required to minimize dilution to avoid cracking while producing acceptable penetration and fusion. GTAW of cast
irons is usually limited to repair of small parts. Nickelbased filler metals are recommended because they
minimize cracking due to their higher ductility and their
tolerance for hydrogen. Cracking can also be minimized
by preheat and postweld heat treatment. DCEN is recommended, although AC may be used.
11.9 Cobalt Alloys. Cobalt alloys are considered very
weldable (see Figure 77) and the same comments made
for stainless steels are applicable. During welding, cobalt
alloys can adversely react with copper to form cracks.
Copper contamination can be picked up from hold-down
tooling, heat sinks, or backup bars. A remedy for this is
to either plate the copper fixture with nickel or chrome or
make it from austenitic stainless steel.
11.12 Welding Dissimilar Materials. Iron, nickel and
cobalt base alloys that are considered weldable can generally be joined to other weldable iron, nickel and cobalt
base alloys via the GTAW process. Other alloy systems,
such as aluminum, beryllium, titanium, magnesium, and
the refractory metals can be readily joined, via GTAW,
only within the same alloy system.
When welding dissimilar base metals, the differences
in properties between the two different metals must be
considered, such as thermal expansion, heat-treatment
response, hot cracking, corrosion resistance, and mechanical properties. Nickel or austenitic stainless steel
filler metals are often used on other alloys, such as ironbase alloys where the weldment cannot be postweld heattreated, because these fillers provide improved ductility.
11.10 Refractory and Reactive Metals. GTAW is the
most extensively used welding process for joining of
refractory and reactive metals. Refractory metals (notably tungsten, molybdenum, tantalum, niobium (also
called columbium), and chromium) have extremely high
melting temperatures and, like the reactive metals (such
as titanium,94 zirconium, and hafnium alloys), are readily
oxidized at elevated temperatures unless protected by an
inert gas cover. Absorption of impurities such as oxygen,
nitrogen, hydrogen, and carbon will decrease toughness
and ductility of the weld metal.
For these metals and alloys, GTAW provides a high
concentration of heat and the greatest control over heat
11.13 Filler Metals. Filler metals for gas tungsten arc
welding are available in many forms (e.g., straight rods,
spooled wires, and consumable inserts), as previously
discussed in 9.2.6. Filler metals are available for gas
tungsten arc welding for many different alloys. Filler
metal compositions and requirements for gas tungsten
arc welding are found in AWS specifications, which are
summarized in Table 20.
93. Hastelloy is a trademark of Haynes International,
Incorporated.
94. “Gas Tungsten Arc Welding: It’s Built to Handle Titanium.” Welding Journal, Vol. 70, No. 11, Nov. 1991, pp. 31–
36.
92
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 76—High Quality Welds in Inconel 718,
Original Scale 5X
Figure 77—High Quality Welds in Cobalt Alloy HS188,
Original Scale 5X
93
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
AWS C5.5/C5.5M:2003
Figure 78—Manual GTAW of Titanium in an Inert Gas Chamber (Glove Box)
12. Qualification of Procedures,
Welders, and Welding Operators
product is being manufactured will normally identify
which of the WPS variables are qualification (or essential) variables. Qualification variables are items in the
WPS that if changed beyond specified limits, require
requalification of the welding procedure. After requalification, a revised or new WPS should be prepared. Variables other than qualification variables (or nonessential
variables) are items in the WPS that may be changed, but
the changes do not affect the qualification status. All
changes in the procedure require a revision to the written
WPS prior to using the revised procedure in production.
Normally, a procedure specification must be qualified by
demonstrating that joints made by the procedure can
meet prescribed requirements. The actual welding conditions used to produce an acceptable test joint and the results of the qualification tests are recorded in a Procedure
Qualification Record (PQR).
Welders or welding operators are normally required
to demonstrate their ability to produce welded joints that
meet prescribed standards. This is documented in a
Welder Performance Qualification (WPQ) record or a
Welding Operator Performance Qualification (WOPQ)
record.
An authorized representative of the organization performing the qualification tests must certify the results of
the welding procedure or performance qualification. This
is known as certification.
12.1 Introduction. Most fabricating codes and standards
require qualification of welding and brazing procedures
and of welders, brazers, and operators who perform
welding and brazing operations. Standards or contractual
documents may also require that weldments or brazements be evaluated for acceptance by a qualified inspector. Nondestructive inspection of joints may be required.
Qualified nondestructive testing personnel using specified testing procedures should perform such inspections.
Technical societies, trade associations, and government agencies have defined qualification requirements
for welded fabrications in standards generally tailored
for specific applications such as buildings, bridges,
cranes, piping, boilers, and pressure vessels. Welding
procedure qualification performed for one standard may
qualify for another standard provided the qualification
test results meet the requirements of the latter. The objectives of qualification are the same in nearly all cases.
Some standards permit acceptance of previous performance qualification by welders and welding operators
having properly documented evidence.
A Welding Procedure Specification (WPS) is a document that provides in detail required welding conditions
for a specific application. The standard to which the
94
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
1. ACCEPTABLE—SILVER WELD METAL
2. ACCEPTABLE—STRAW COLOR IN WELD
METAL AND HEAT-AFFECTED ZONE
(HAZ)
3. ACCEPTABLE—LIGHT BLUE AND STRAW
COLOR IN HEAT-AFFECTED ZONE (HAZ)
4. NOT ACCEPTABLE—DARK BLUE COLOR
IN WELD METAL AND HEAT-AFFECTED
ZONE (HAZ)
5. NOT ACCEPTABLE—SEVERE
DISCOLORATION IN WELD METAL
6. NOT ACCEPTABLE—GRAY DEPOSITS IN
WELD METAL
Figure 79—Criteria for Acceptable GTAW in Titanium via Tack Welds Only
95
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
12.2 Welding Program. A company expecting to produce quality weldments to the requirements of codes,
standards and specifications, herein referred to as specifications, should have a formal program defining the administrative control of welding. This program should
include: procedures covering welding requirements, procedures controlling weld filler material and materials to
be welded, documentation supporting welder/welding
operator and procedure qualifications, and proof that the
welding being performed was in conformance with the
acceptance criteria of the specification. A company
manufacturing or fabricating welded components that
are not covered by codes should follow the guidelines of
the codes that are the most applicable to their welding
applications.
12.4.1 Qualification Procedures. Confusion sometimes exists between a WPS and a similar document,
given various names, to define the welding to be done by
a welder or welding operator to become qualified.
Some documents, e.g., MIL-STD-2219, use the term
“Welding Procedure Qualification” when in fact they
mean a WPS with a PQR showing the weld was
qualified.
12.4.2 Standard Welding Procedure Specifications.
AWS B2.1 provides requirements for qualification of
welding procedures and personnel. It also references
AWS B2.1Xxxx, Standard WPSs. The pertinent AWS
Standard WPSs for GTAW are listed in Section 2.
12.5 Procedure Qualification Records (PQR). A Procedure Qualification Record (PQR) is a record of the
welding variables used to weld a test coupon. It also
contains the test results of the tests required, which are
usually mechanical tests. Recorded variables normally
fall within a small range of the actual variables that will
be used in production welding.
The PQR documents all essential and supplementary
essential (when required) variables for each welding
process used during the welding of the test coupon. Recording of nonessential or other variables used during the
welding of the test coupon is optional.
12.3 Establishing Welding Requirements. Welding requirements are as described by the specification. These
documents specify inspection requirements and acceptance criteria for welding as well as joint designs, workmanship, preheat, interpass temperature, postweld heat
treatment and specify, or defer to, another document for
welding procedure and welder performance qualification
requirements. Some of the national welding documents
are under the jurisdiction of:
(1) American Welding Society (AWS)
(2) American Society of Mechanical Engineers
(ASME)
(3) American National Standards Institute (ANSI)
(4) American Petroleum Institute (API)
(5) American Bureau of Shipping (ABS)
(6) Federal Government MIL-STDs, U.S. Coast
Guard and NAVSHIPS/NAVSEA
(7) Compressed Gas Association (CGA)
12.5.1 Qualification (Essential) Variable (Procedure). A change in a welding condition which will affect
the mechanical properties (other than notch toughness)
of the weldment (e.g., change in the welding process,
filler metal, electrode, preheat, postweld heat treatment
(PWHT), or a change in base metal composition). Some
documents cover composition via a “P-number” which
permits minor compositional changes. Examples of
GTAW essential variables may include: type of tungsten,
backing gas, purge gas, and the use of a consumable
insert.
12.4 Welding Procedure Specifications (WPS). A
WPS is a written qualified procedure prepared to provide
direction to the welder/welding operator for making production welds. The usual information contained in a
WPS for GTAW includes:
(1) Limitations (e.g., thickness or diameter)
(2) Joint Designs Allowed
(3) Base Metals
(4) Filler Metals (e.g., types and sizes and wire feed
rates)
(5) Welding Position
(6) Preheat, if applicable
(7) Interpass Temperature, if applicable
(8) Postweld Heat Treatment, if required
(9) Shielding Gas (e.g., type, purity, and flow rates)
(10) Purging Requirements
(11) Electrical Characteristics (e.g., type, amperage,
and voltage)
(12) Tungsten Electrode Type and Size
(13) Technique (e.g., stringer bead or weave bead)
12.5.2 Supplementary Essential Variable (Procedure). A change in a welding condition which could affect the notch-toughness properties of a weldment (e.g.,
change in the direction [uphill to downhill] for vertical
welding, heat input, preheat or PWHT, etc.).
12.5.3 Nonessential Variable (Procedure). A
change in a welding condition which will not affect the
mechanical properties of a weldment (e.g., method of
back gouging, cleaning, etc.).
12.6 Welder and Welding Operator Qualification
Tests. Welder and welding operator qualification tests
primarily are given to determine their ability to produce
sound welds that meet the requirements of the particular
document involved. There are numerous types of qualification tests depending on the requirements of the appli-
96
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
cation. However, the test should be designed to represent
the type of work the welder/welding operator will be required to do.
There are many misunderstandings of the terms “qualification,” “qualified welder,” and “certified welder” because there are so many different organizations that have
issued requirements for welding. The following explanations should help clarify these misunderstandings.
13.2 Weldment Quality. GTAW weld quality relates directly to the integrity of the weldment. It underlies all of
the fabrication and inspection steps necessary to ensure
that a welded product will be capable of serving the intended function for the desired life. Both economics and
safety influence weld quality considerations. Economics
require that a product must be competitive, and safety requires that the product function without hazard to personnel or property.
The majority of welded fabrication standards define
quality requirements to ensure safe operation in service.
(Standards are discussed in Chapter 13 of the AWS
Welding Handbook, 8th Edition, Volume 1, Welding
Technology).
The requirements of such standards are to be considered minimums, and the acceptance criteria for welds
should not be encroached upon without sound engineering judgment. For critical applications, more stringent requirements than those specified in the fabrication
standard may be necessary to ensure the highest degree
of safety.
Initial areas of quality concern are that the materials,
heat treatments, preparations and processing have been
properly verified and documented. Weld quality is usually verified by nondestructive examination (NDE). The
first NDE to be used is visual examination by the welder,
prior to the weldment leaving for the next operation. The
acceptance standards for the welds are generally related
to the method of nondestructive examination. All deviations are evaluated, and the acceptance or rejection of a
weld is usually based on well-defined conditions. Rewelding or repair of unacceptable or defective conditions
is allowed if properly qualified and approved so that the
quality of the weld may be brought up to acceptance
standards.
Common methods of nondestructive examination
(NDE) applied to weldments are as follows:
(1) Visual Inspection
(2) Radiographic (X-ray)
(3) Magnetic Particle
(4) Dye Penetrant
(5) Fluorescent Penetrant
(6) Ultrasonic Inspection
(7) Eddy Current
12.6.1 Qualification and Qualified Welder/Welding Operator. A qualification is a test given to determine the individual’s ability to make a weld according to
the requirements of a particular document. Once the test
is passed, the individual now becomes a “qualified
welder” however; the individual is only “qualified” according to the particular document and not to all others.
Generally a welder must weld within prescribed time
limitations, usually six months, for his qualification to
remain in effect. Most documents specify fewer restrictions for requalification.
Since there are so many different requirements for
welding, a welder who is qualified to the requirements for
one document is not necessarily qualified to weld under
another, even though the tests are similar. For example,
some documents may require vision or written exams in
addition to an actual weld. Because of these differences,
companies and individual welders should be familiar with
the specific requirements for each application.
12.6.2 Qualification and Certification. The proper
term is “qualified welder,” not “certified welder.” The
term certified should not be used; the correct terminology is “welder qualification or welding operator qualification.” One part of the qualification is the
documentation (certification) that is prepared by the organization conducting the test. The qualification record
states that the testing agency (Military, Government
agency, company, owner, or contractor) has witnessed
the preparation of the test coupon(s), and has tested them
according to the applicable requirements and that the
welder has successfully completed all of the requirements. Certification is the documentation that the person
is qualified.
13. Quality Control
A detailed discussion of Overall Weld Quality can be
found in the AWS Welding Handbook, 8th Edition, Volume 1: Chapter 11, pp. 350–383.
13.1 Introduction. Quality is a relative term and can be
defined as the “conformance to a specification.” If a
weldment conforms to the specification then it is considered a quality product. To have higher quality than is
needed for the application is not only unnecessary, it is
also often costly. Thus, quality levels may be permitted
to vary among different weldments and individual welds,
depending on their service requirements.
13.3 Specifications. Specifications include the requirements on the product drawings. The purpose of any inspection is to ensure a predetermined quality level in the
finished product. Since the requirements may vary
widely with service conditions, design factors and economics, each manufacturing company must establish a
97
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
quality level that applies to its specific product. The company’s specification must define the test method and acceptance criteria to assure uniformity in testing and
evaluation of the product.
turer’s manuals is particularly suited to solving of problems at this level.
14.2 Electrical. Many times equipment-related welding
problems are caused by the poor condition of the cables
or by loose and/or corroded connections. If problems are
encountered, it is often helpful to first inspect the cables
and connections. If the symptoms are erratic behavior of
a specific variable such as weld current, one might physically move the position of the welding cables both near
the power supply and at the welding torch or fixture.
This could find a cause-and-effect relationship between
the cable position and the instability of the arc current.
Care should be used, since if the cables are faulty, there
is very strong possibility of electric shock. Electrical
conductors and connectors need to be inspected on all
sensors and measuring devices. Since sensors are many
times located inside of the welding power source, near
high voltage, safety precautions in accordance with the
manufacturer’s recommendations must be observed.
14. Troubleshooting
14.1 General. To consistently achieve high quality gas
tungsten arc welds the important welding parameters, recorded in a WPS (Welding Procedure Specification),
must be followed. Furthermore, the welding equipment
must be operating correctly and the weld tooling/fixturing
must be functioning correctly. Finally, the skill level of
the welder or welding operator must be adequate for the
specific weld and these welding personnel must do their
job correctly. The following illustration shows the importance of skill level.
The quality department of a jet engine manufacturer
tracked the number of defects, mostly minor dimensional
ones, on a complex welded assembly. The number of defects consistently ran in the 0 to 3 range for each assembly and 3 to 4 assemblies were made per week. This rate
of defects was quite constant for over a year. Suddenly
the number of defects jumped to greater than 25 per assembly. This was traced to the fact that the welder who
had been welding the assembly retired and a new welder
had been assigned. While skill level is an important factor it is very difficult to quantify. Thus, the contribution
of welder skill and training on weld quality will only be
addressed peripherally. Most of this section will deal
with the effects of tooling, environment and equipment
on weldments, and will consider all other factors to be
constant.
14.2.1 Welding Power Stability. Voltage variations
in the utility power coming to the welding equipment can
adversely affect the weld quality if the voltage is not
compensated or controlled. These variations may be
caused by the power company or by other users on the
same substation line. An example of a cause for sudden
fluctuations is the turning on or off of a large motor.
Voltage variations can consist of two types: (1) high or
excess voltage and (2) low or insufficient voltage. When
a problem with power fluctuations is suspected, a voltage
recorder that will measure transients should be plugged
into the line. Many companies that calibrate gages or rent
industrial instruments have line voltage recorders that
can be rented or temporarily installed. Such recorders
provide a record of voltage transients coupled with the
time of day. Thus, if a weld problem occurred slightly
after 3:00 PM and the record shows there was a voltage
surge at 3:04 PM, the two events can be correlated.
Therefore, it can be determined if voltage fluctuations
are the cause of the welding problems.
If the problem is voltage spikes, sometimes called
voltage surges, the solution is relatively simple. A voltage stabilizer can be added to the incoming line voltage.
Basically, this is a passive device that can maintain a
constant voltage output to the welding equipment with a
varying input voltage. Some of the newer welding power
supplies have built-in line voltage compensation, which
can continuously compensate for line voltage fluctuations. If compensation is not built in to the welding
power source and if a voltage stabilizer does not remedy
the problem, the services of an electrical contractor or
engineer may be required. When a power fluctuation
problem is suspected and the recorder shows no correlation, e.g., the welding problem occurred about 2:15 and
Troubleshooting, as used in this publication, is the determination of the root cause of why a weld is now defective, when it was made successfully in the past. The
troubleshooting factors, which will be considered in this
section, follow the major equipment items listed in Table
19. Additional possible causes and remedies are outlined
in Table 21. In general, the welder has an idea of what is
causing the weld to be defective, and this section will
deal with not only finding the root causes of defective
welds, but will offer some suggestions at remedying the
problem.
Manufacturers of welding equipment will often provide excellent troubleshooting in their equipment installation and/or operating manual. These guides provide
more equipment specific information than can be provided in the necessarily more general data in this document. Many times the treatment of welding and
equipment problems needs to be addressed at the circuit
board and interconnection level. Use of the manufac-
98
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Table 21
Troubleshooting
Table
21 (Continued)
Problem
Excessive
Electrode
Consumption
Erratic Arc
Possible Cause
Possible Remedies
1. Inadequate gas flow.
1. Increase gas flow.
2. Operating on DCEP (reverse polarity).
2. Use larger electrode or change to DCEN (straight
polarity).
3. Improper size electrode or too sharp a tip for
current required.
3. Use larger electrode or correct tip shape.
4. Excessive heating in holder.
4. Check for proper concentricity and contact with
collet and tighten if necessary.
5. Contaminated electrode.
5. Remove contaminated portion. Erratic results will
continue as long as contamination exists.
6. Electrode oxidation during cooling.
6. Keep inert gas flowing after extinguishing arc for
15 seconds.
7. Using gas containing oxygen, or carbon dioxide.
7. Change to proper gas or see text regarding gas
purity problems.
1. Base metal is dirty or greasy.
1. Use appropriate chemical cleaners, wire brush or
abrasives.
2. Joint is too narrow.
2. Open joint groove; bring electrode closer to work;
decrease voltage.
3. Electrode is contaminated.
3. Remove contaminated portion of electrode.
4. Arc is too long.
4. Shorten arc.
5. Magnetic fields are affecting the arc.
5. Degauss base metal and tooling; rearrange
workpiece connection. Use magnetic arc
stabilizer.
6. Incorrect electrode size.
6. Use electrode with minimum diameter that will
handle maximum current.
7. Inert gas flow problems.
7. Check flow control system and sufficiency of
inert gas supply.
8. Tungsten tip: irregular shape, bad tip finish, tip
ground in non-axial direction.
8. Use properly prepared tungsten tip.
1. Entrapped gas impurities (hydrogen, nitrogen, air,
water vapor, etc.)
1. Purge all air from lines before striking arc;
remove condensed moisture from lines and work;
use welding grade inert gas
2. Defective gas hose or loose hose connection
2. Check hose and connections for leaks. Do not use
rubber hoses. Viton or polyethylene hoses are
acceptable. Replace all contaminated hoses.
3. Oil film on base metal.
3. Clean with approved chemical cleaner. DO NOT
WELD WHILE BASE METAL IS STILL DAMP.
4. Contaminated filler metal.
4. Clean filler metal or use uncontaminated (fresh)
supply.
5. Base metal has high gas content or impurities,
particularly prevalent with castings.
5. Use different base metal; use multiple low
penetration passes.
6. Dye penetrant inspection media not completely
removed.
6. Grind out base metal until all traces of penetrant
are removed.
Porosity
(Continued)
99
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Table 21 (Continued)
Problem
Tungsten
Contaminates
Weld Metal
Weld Bead Size
Inconsistent
Oxidation of
Weldment
Insufficient
Penetration
Lack of Fusion
Possible Cause
Possible Remedies
1. Contact starting with tungsten electrode.
1. Use high-frequency or other starter. Use copper
striker plate.
2. Electrode melting and alloying with base metal.
2. Use less current (particularly during arc starting)
or use larger electrode.
3. Touching electrode to molten pool
3. Use longer arc length.
4. Weld current too high or too erratic.
4. Reduce arc current or increase electrode size.
1. Uneven travel speed
1. Use solid-state or closed loop feedback speed
controls.
2. Welding power instability.
2. Replace electrical components that are in poor
condition. Use correct sizes.
3. Erratic wire feed.
3. Use proper filler wire feed; tighten wire feed and
straightening rolls
1. Insufficient shielding gas flow.
1. Increase gas flow and possibly cup size.
2. Contamination of inert gas hose or regulator.
Incorrect torch assembly.
2. Replace, retighten, or repair hose and torch parts.
3. Cup size too small.
3. Use sufficient cup size for welding current, travel
speed and gas flow.
4. Improper environment, such as wind above
5 mph.
4. Shield welding area by erecting a shelter or wind
block.
5. Dirty or wet workpiece or filler metal.
5. Clean and dry workpiece just prior to welding and
use clean, dry filler metal.
6. Travel speed too fast.
6. Decrease travel speed.
7. Excessive oxide on workpiece.
7. Grind or machine all excessive oxides from
surfaces to be welded.
1. Poor weld joint design or uneven preparation.
1. Change joint design; prepare joint correctly;
reduce weld thickness.
2. Incorrect electrode tip shape.
2. Regrind electrode for flatter angle.
3. Insufficient welding current.
3. Increase welding current.
4. Incorrect gas mix.
4. Use more helium to increase penetration.
5. Travel speed too fast.
5. Decrease travel speed.
6. Arc length too long.
6. Decrease arc length.
7. Weldment has excessive oxide coating.
7. Grind or machine all surfaces to be welded.
1. Insufficient welding current.
1. Increase welding current.
2. Travel speed too fast.
2. Reduce travel speed.
3. Filler wire diameter too large.
3. Decrease filler wire diameter.
4. Arc blow.
4. Change the position of the workpiece connection
or weld toward the workpiece connection. Remove
magnetic fixturing from immediate arc area.
5. Heavy oxide coating on weld joint.
5. Grind, machine, or chemically remove oxides
from welding area.
(Continued)
100
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Table 21 (Continued)
Problem
Lack of Fusion
(cont’d)
Excessive
Distortion
Cracking
Arc Fails to Initiate
Possible Cause
Possible Remedies
6. Incorrect gas mix.
6. Use proper hydrogen mix for most stainless steels
and nickel alloys.
1. Excessive welding current.
1. Reduce welding current or reduce travel speed.
2. Poor design.
2. Use joint designs that add restraint or require less
welding.
3. Improper pass sequencing or number of passes.
3. Use improved procedures to accommodate joint
design.
4. Improper tooling.
4. Apply sufficient constraint along weld joint with
adequate heat sinks.
1. Geometric restraint.
1. Use correct joint designs that avoid excessive
restraint.
2. Thermal stresses.
2. Weld more passes for less heat input.
3. Insufficient root thickness.
3. Travel speed should be lower or weld current
higher.
4. Grain boundary liquation.
(Hot cracking)
4. Use correct welding speed and current to reduce
weldment melting. Use proper filler metal that is
free of low melting constituents.
5. Metallurgical imbalances or phase changes.
5. Use correct filler metal for the base metal being
welded.
6. Filler metal problems.
6. Filler metal should be added at the correct rate for
the travel speed and weld current selected.
1. Power source not plugged in or turned on.
1. Plug in power supply and check to see if it can be
turned on.
2. Power source fuse blown or not seated properly.
2. Replace or insert fuse properly. Be sure fuse is
correct size and to locate cause of blown fuse.
3. Mechanical circuit breaker has tripped
3. Reset circuit breaker. Be sure to find and correct
cause
4. Thermal overload protector turned off power
source.
4. Wait until thermal overload protector cools down.
Be sure to operate power source within the rated
duty cycle.
5. Electrode in poor condition.
5. Grind electrode to correct shape.
6. Weldment has heavy oxide coating.
6. Grind or machine surfaces to be welded.
7. Loose or missing workpiece connection.
7. Make proper workpiece connection.
the recorder shows no sign of a transient between 2:00
and 2:30, the welding power supply may be suspect. In
such instances, the manufacturer’s operating manual is
often the best source of information.
Manufacturers of arc starting units have specific installation requirements to address necessary safety considerations that must be met for high voltage applications
and to prevent interference with other types of equipment. Radiated signals and conducted signals can affect
other welding equipment and other sensitive electronic
equipment if not properly installed, shielded, or isolated. The high-frequency current associated with arc
14.2.2 High-Frequency Current. High-frequency
current is used for starting the arc and is sometimes
superimposed continuously during AC or VP welding.
101
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
starting normally does not create a problem with the
weldment.
14.2.3 Magnetic Fields and Arc Blow. It is a fact of
physics that an electric current will create a magnetic
field. It is also a fact of physics that a magnetic field will
interact with an electric current. Since an arc plasma conducts electric current, it can be deflected by a magnetic
field. This arc deflection, wandering or bowing by a
magnetic field, when it occurs to a discernible extent, is
called arc blow. Magnetic deflection of the arc should
not be confused with disruption of the inert gas flow,
caused by wind currents, which will be discussed later.
Arc blow may occur to such an extent that the arc cannot
be controlled and thus an unacceptable weld is produced.
The common ferromagnetic materials95, e.g., plain carbon and low alloy steels, may be involved in the welding
process as base metals, filler metals and/or tooling.
When there are no ferromagnetic materials involved in
the welding operation, changing the magnetic field created by the electric current is often adequate to provide
arc stability. This may simply involve the movement of
the work cable to a different location, or insuring that the
power leads are not in close proximity to the arc, particularly if they are coiled. While changing the location of
electric current relative to the arc may also work with
ferromagnetic materials; ferromagnetic alloys may need
to be demagnetized, which is often referred to as degaussing. The amount of arc deflection is directly related
to the strength of the offending magnetic field and its orientation relative to the arc. As the strength increases and
the field becomes more perpendicular to the arc, the
amount of deflection increases. Because of these facts,
and the fact that cables which carry high current create a
magnetic field, the relative position of the cables can
change the amount of arc deflection.
As noted previously, a magnetic field is produced
when an electric current is present. With nonferromagnetic materials, when that current is turned off, the magnetic field decays immediately to zero. With
ferromagnetic materials, the effect of the magnetic field
is normally magnified and when the current is turned off
there will still be a magnetic field present. The amount of
magnetic field still present is based upon the retentivity
of the ferromagnetic material. If the retentivity96 of the
material is low, it is said to be “soft” magnetically. Conversely, if the retentivity of the material is high, it is said
to be “hard” magnetically. Many of the low alloy steels,
frequently used to make jaw chucks, turn tables and
other tooling, are hard magnetically. Under repeated use
in welding operations, the residual magnetic fields may
create problems. Thus, fixturing as well as the assembly
to be welded must often be demagnetized.
All of the ways of demagnetizing a part are based
upon the same principle. The part is subjected to a magnetic field continually reversing its direction and at the
same time gradually decreasing in strength to zero. For
this principle to work, the magnetizing force must be of a
high enough intensity, or coercive force, at the start to
overcome the residual magnetism and to reverse the residual field (retentivity) initially in the part. Also the incremental decrease between successive reductions in
current must be small enough so that the reverse magnetizing force will be able to reverse the field remaining in
the part from the last previous cycle reversal. In some
highly magnetic materials, demagnetization can occur as
soon as they are exposed to even weak magnetic fields.
For small to medium size parts, a common method of
demagnetization is to pass them through a coil connected
to an AC power source. Often line frequency (about
60 Hz) is adequate. Alternatively, the parts can be placed
inside a coil and the current level gradually reduced to
zero. In the first method, physically moving a part
through a coil, the strength of the reversing field is reduced, effectively to zero, by axially withdrawing the
part from the coil and for some distance beyond the end
of the coil. For the other method, gradual decay of the
current in the coil accomplishes the same thing. Use of
baskets or trays to pass small parts through the coil is not
recommended unless the parts can be placed on a tray in
a single layer, spaced apart and with their long axes parallel to the axis of the coil. Demagnetization (or degaussing) coils are often available at facilities that do magnetic
particle inspection and are sold by companies that supply
magnetic particle inspection equipment.
Demagnetization of larger parts is often more difficult
since one needs a lower frequency (e.g., 25 Hz) AC or a
95. Materials containing the elements iron, nickel, or cobalt can
be magnetized or affected by a magnetic field.
96. Retentively is the power of retaining or the capacity of
retaining magnetism after the action of magnetizing has ceased.
Problems normally occur with either older equipment
or when an arc starter unit is added to an existing power
supply. Incorrectly installed units can have deleterious
influences upon nearby electronic and communication
systems. Some companies have built special welding
rooms to retain the high-frequency current within specified limits.
GTAW with high frequency could create a safety hazard in that the current will follow the path of least resistance, which could be the welder’s body. To prevent
such an occurrence, the work cable should be as close to
the arc as possible. This will shorten the distance of current travel and help ensure that the welder does not become the shortest path to ground.
102
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
reversible DC which is commonly operated in the 1 Hz–
2 Hz range. Lower frequency is required to completely
penetrate large cross sections. Another technique that has
been used to compensate for arc blow is to construct a
coil that will create a compensatory magnetic field.
These coils have ranged in complexity from simply coiling the power leads to a specifically designed standalone system.
(6) Defects such as splits or cracks in the electrode.
(7) Inadequate shielding gas flow rates or excessive
wind drafts which result in oxidation of the electrode tip.
(8) Use of improper shielding gases or mixtures that
result in oxidation of the electrode tip.
Corrective steps are normally obvious once the causes
are recognized and the welder/welding operator is adequately trained.
14.2.4 Tungsten Electrodes. Since the electrodes are
part of the electrical circuit, they will be discussed under
electrical troubleshooting. The advantages/disadvantages
of the various types of electrode alloys are discussed in
detail in most suppliers’ literature. In general, with “standard” straight polarity DC welding (DCEN), one should
have the smallest diameter electrode that will handle the
maximum current without balling. Balling and having an
electrode too large in diameter (for the current being carried) can cause arc wander. Arc wander often produces
very poor quality joints since the temperature on the
weldment will vary substantially as will the location of
the molten pool. With AC or DCEP welding, balling of
the electrode is normally required due to the increased
heating of the electrode. However, too large a diameter
ball or too large an electrode diameter for the current
being carried can produce arc wander.
Another problem, which is unique to GTAW, is the
inclusion of particles of tungsten or tungsten alloy, from
the electrode, in the actual weldment. These are often
called tungsten inclusions, high-density inclusions or
tungsten contamination. During radiographic inspection
(X-ray) these show up as white spots on the film. Due to
the increased heating of the electrode during AC, some
types of VP and DCEP welding, they are normally created only when these current types and polarities are
used. Thus, such inclusions are very common in aluminum and magnesium weldments. Depending upon the
number of inclusions and the inspection standard being
applied, these tungsten inclusions may or may not need
to be removed. While the most common cause of tungsten inclusions is exceeding the current limit for a given
electrode size and type, some other typical causes are the
following:
(1) Contact of the electrode tip with the molten weld
puddle.
(2) Contact of filler metal with the hot tip of the electrode, which will cause a lower melting alloy.
(3) Contamination of the electrode tip by spatter from
the weld puddle.
(4) Extension of the electrodes beyond their normal
distances from the collet resulting in overheating of the
electrode.
(5) Inadequate tightening of the holding collet or
electrode chuck so that the electrode overheats due to inadequate cooling from the holding mechanism.
14.3 Inert Shielding Gas Troubleshooting
14.3.1 Flow of Shielding Gas. The proper flow of
shielding gas is a very important factor for high quality
GTAW weldments. Insufficient or excessive amounts of
shielding gas can have negative effects on welding quality. Excessive gas can cause turbulence to occur and air
contamination to be introduced; causing oxidation and
discoloration of the weld deposit. Insufficient gas flow
can also result in poorly protected welds, that is, oxidation from the air can occur, and once again oxidized and
discolored weld deposits can be produced. While discolored deposits may appear only to be cosmetically displeasing, the presence of oxide can reduce mechanical
properties (strength and fatigue) and reduce toughness.
Excessive or insufficient gas flow can usually be corrected by adjusting the flow rate of the shielding gas.
Thus, gas flow should be considered an “essential variable” and correctly filed on the appropriate welding procedure. As discussed below, if weld discoloration
persists after adjusting of the gas flow rate, it is likely
that there is another cause. Potential other causes are discussed in 14.3.2 through 14.3.7.
14.3.2 Inert Gas Pressure Stability. The stability of
the inert gas pressure at the GTAW torch is highly critical to weld quality. Unstable gas pressure will manifest
itself in the same manner as improper flow (noted in
14.3.1). The main difference will be that the discoloration of the weldment will often be spotty. That is, the intensity and amount of oxidation will vary if there is a
pressure stability problem, while with a flow problem the
amount of oxidation (discoloration) will tend to be a little
more uniform. The most common causes of pressure instability are the gas control regulators and/or flowmeters,
which will be discussed later. Thus, the volume of
shielding gas will vary at the torch gas nozzle or cup. Atmospheric gases can be pulled into the shielding gas
stream with both excessive and inadequate flow rates.
Therefore, shielding gas flow must be controlled within a
minimum and maximum range as specified in the welding procedure. Many welders who have had trouble
welding titanium alloys have tried to correct shielding
problems by increasing the inert gas flow from the
GTAW torch gas nozzle or cup. The increased gas flow
only causes a greater problem by aspirating air into the
shielding gas via turbulence. Decreasing the gas flow to
103
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
a level that does not cause turbulence, yet is adequate to
provide for proper shielding, and the addition of a trailing shield to cover the recently solidified hot metal are
normally more successful than increasing the gas flow.
chamber. Such a test should be run at various locations
inside the chamber to ensure that a sufficient amount of
air has been removed. Some shielding gases, notably argon, are heavier or denser than air. Thus if argon shielding is to be used, the atmosphere should be checked near
the top of the chamber. Conversely, if helium shielding is
to be used, the atmosphere should be checked near the
bottom of the chamber because helium is lighter than air
and rises.
14.3.3 Gas Purity. The purity of inert shielding gases
is paramount to acceptable weld joint quality for many
precision applications, such as for welding in the semiconductor and bio-technology industries and for welding
reactive metals such as titanium and zirconium. Lack of
purity or contamination can also adversely affect routine,
nonprecision weldments. A quick and effective way to
check a cylinder of inert shielding gas for purity is to
strike an arc on a piece of properly cleaned titanium. The
resultant weld must be measured against a known purity
of inert gas tested under the same conditions. A pure
shielding gas will cause the weld spot or weld bead to be
bright, shiny and clear. Any discoloration will indicate
nitrogen, oxygen, water, and/or hydrocarbons in the cylinder of gas being tested. Stainless steel may also be used
for this test, but it is not as sensitive.
Even if the gas cylinder contains “pure” gas, the
hoses, fittings, lines or other parts of the gas delivery system may be defective or loose, causing the gas to become
contaminated. Check all systems from the cylinder exit
to the torch gas nozzle or cup for all factors that would
allow air or moisture into the system. For example, there
may be condensed water in the lines or system. There are
many ways that moisture can get into the delivery system
and the source(s) need to be identified and eliminated.
14.3.4 Gas Nozzle (Cup) Sizes, Types, and Cleanliness. The gas nozzle of the welding torch must be properly sized and selected for the specific application in
which it is used. A small gas nozzle size may enhance
welder visibility, but may not provide adequate gas
shielding of the molten weld pool.
Torch angle is also important, as excessive tilt97 can
result in ambient air being drawn into the gas stream,
thus contaminating the shielding gas and the molten weld
pool, and affecting the heat-affected zone. Often this
problem is difficult to detect and may require a second
welder’s observation before it can be detected.
A gas lens will generally provide much better gas
coverage than a standard nozzle or cup. The precision
screening device or highly porous sintered bronze in the
end of the gas lens produces an even and constant gas
flow which produces a nonturbulent or gentle flow of gas
over the weld pool. Figure 24 illustrates, via a “tracer” in
the argon gas, the difference in gas flow with and without a gas lens. Note that the left torch, which does not
have a gas lens, produces a more turbulent flow of the
shielding gas.
The shielding gas for the welding torch is usually delivered from the source to the torch through a rubber or
plastic hose. Gas-cooled torches have the inert gas flowing in the same hose as the power cable. Water-cooled
torches will normally have a separate line for the inert
gas and input water, while the return water will be carried in the same hose as the welding power cable. With
individual hoses and cables the defects are easier to locate and repair than if a hose has a multiple function. For
example, there may be an internal water leak between the
cooling water and inert gas if one hose is utilized to carry
both. These consolidated hose bundles are easier to manipulate during the welding operation but are more difficult to troubleshoot.
Also, hose fittings may be loose or damaged, causing
contamination of the shielding gases by aspiration of air.
The fittings on the torch and those inside of a power
source should be checked. The latter fittings are often
overlooked because they are concealed from view.
Welding in an inert gas chamber involves testing the
purity of the gas inside the chamber. One of the more
commonly used techniques is to run a bead on a piece of
properly cleaned titanium. Figure 79 provides visual criteria on the acceptability of the gas purity inside the
Cracks in the shielding gas nozzle or cup, a loose fitting cup or gas lens, damaged gaskets, defective insulators, improper threads, or plugging of cup or gas lens due
to weld spatter are other potential sources of air/water
contamination. For special or unusual requirements, such
as using a nonrecommended size gas nozzle, a test may
need to be conducted with the modified system to ensure
that the weldment is properly shielded.
14.3.5 Trailing Shields. Trailing shields are used for
welding materials, such as titanium and zirconium,
which are very sensitive to atmospheric contamination
even after they have solidified. That is, they can pick up
oxygen from the atmosphere at temperatures above
1000°F [538°C], while their solidification temperatures
are greater than 2000°F [1093°C]. Trailing shields may
also be used to cover any material when high travel
speeds are employed, since the weld may still be molten
after the shielding gas cover from the nozzle has passed.
97. Tilt is the angle through the centerline of the torch and the
direction of weld travel.
104
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Atmospheric impurities can enter from underneath the
trailing shield through the inert gas supply hose and from
the connection between the trailing shield and the torch
nozzle or cup. Heat-resistant flexible side curtains or
skirts can be placed around the edge of the trailing shield
to minimize air incursion from outside the fixture. Flexible glass cloth* and some silicon based elastomeric materials, such as silicone rubber, have also been
successfully used as skirts.
The gas supply line fittings connected to the trailing
shield can be silver brazed or welded in place to prevent
the venturi effect of outside air entering into the trailing
gas. The connection between the trailing shield and the
torch nozzle or cup must also be leak tight. One method
that has been successful with copper trailing shields is to
silver braze the shield directly to the ceramic cup. This
hydrocarbon gas torch brazing operation, which normally uses a silver based braze alloy, must be done with
extreme caution to prevent cup cracking, and practice
joints are recommended. Some users have sealed this
joint with high temperature resistant materials such as
fiberglass.*
ing area must be completely shielded from the rain,
wind, snow, etc. In the event of winter conditions (i.e.,
low temperature), the weld enclosure may need portable
hot air or radiant heaters. These heaters will supply comfort to the welder and should keep the base metals above
0°F [–18°C]. They will also prevent the formation of a
very high thermal gradient and the resultant high thermal
stresses and thermal shock in the weldment. Special precautions and attention must also be given to gas lines,
regulators, and water lines to protect them from the
elements. This type of welding should only be carried
out when an emergency is present or no other option is
available.
14.3.7 Regulators and Flowmeters. Defective
shielding gas regulators98 and/or flowmeters may also
adversely affect weld quality by delivering more or less
inert gas than desired. A quick test can be conducted by
replacing a suspected device with a new regulator or
flowmeter. Regulators should also be checked to ensure
that they are set at the proper pressure for the calibrated
flowmeter being used. Two-stage regulators will provide
a more uniform flow as the pressure in the gas cylinder is
reduced.
*Caution must be exercised with fiberglass or glass cloth
since these may utilize low temperature polymeric binders which will outgas when heated and thus could cause
contamination of the weld, present a health hazard, or
both.
14.4 Water Cooling Systems
14.4.1 Water and Water Vapor. Water and water
vapor can cause defects in many different alloy weldments in different ways. For example, with aluminum alloys the normal result is very high porosity while with
stainless steels the normal result is excessive oxidation.
The source of water and water vapor can come from the
cooling system itself, precipitation, or high humidity.
Condensation on joint members or in the torch is another
common problem. This is normally caused when the
cooling water is below ambient temperature or when the
joint members were stored below ambient temperatures
(e.g., outside in the wintertime) prior to welding. Often a
mild preheat (200°F [93°C] to 300°F [149°C]) will prevent problems that result from condensation on the joint
members. Running the purge gas for 2–3 min prior to arc
initiation will often eliminate condensation problems in
the torch. An alternative to running the purge gas is to
weld on some scrap material until the weld shows no
sign of contamination.
14.3.6 Air Movements. Welding personnel need to
understand the importance of controlling the movement
of air in the welding area. Excessive air movement can
disrupt the shielding gas from protecting the molten pool
and HAZ. This can cause excessive oxidation, embrittlement and porosity in the welded joints. Most good
GTAW welders and welding operators can recognize
shielding gas disruptions and correct the circumstances
causing them.
Excessive air movement in buildings can be caused
by fans, opening and closing large doors, and air conditioning or heating system outlets located near the welding station. When welding outdoors, GTAW weldments
usually must be shielded from air movement by welding
behind a protective device, such as a portable curtain or
in some cases within a tent-type or other protective shelter. Such a shelter is normally required when wind velocity reaches approximately 5 mph [8 km/hr].
There may be codes or regulations for a specific application that may add other requirements/restrictions.
For example, AWS D1.1, states: “Welding shall not be
done when the ambient temperature is lower than 0°F [–
18°C], when surfaces are wet or exposed to rain, snow or
high wind velocities.”
When welding outdoors in inclement weather cannot
be avoided, special precautions must be taken. The weld-
14.4.2 Leaks in Fittings and Hoses. The loss of cooling water to the GTAW torch will affect the welding performance in manual, mechanized, or automated
equipment. If water is released onto electrical components, short circuits and malfunctions can occur. It is
98. Bell, D. 1998. “Regulators: Perform Under Pressure,”
Gases and Welding Distributor, Vol. 42, No. 6, November/
December 1998.
105
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
imperative to determine the location of water leaks
quickly and correct them by the necessary means.
(7) Need for backup bars and heat sinks
(8) Need for hold-down fixtures
(9) Shielding gas coverage, root side of joint, trailing
shields
(10) Cost and schedule
(11) Access to joint, including ease of loading and
unloading parts
(12) Can the tooling/fixturing be inadvertently welded
easily?
(13) Can weld spatter quickly make the tooling
inoperative?
(14) Hardness and durability
14.4.3 Cold Weather Operations. A mixture of antifreeze and water in a recirculating system is used in lieu
of water in most cold weather cooling systems. Often a
leak in a system that contains antifreeze is more serious
than a simple water leak because even after the leak is
repaired the residue or corrosion products can “gum up
the works.” Consequently, it is important to check all
hoses and fittings for leakage prior to welding. Defective
hoses or fittings should be replaced and loose fittings
should be tightened.
When GTAW torches are left in cold weather between
welds or between shifts, water condensation may occur
in the torch shielding nozzle or cup. The results on the
weldment will often be the same as if there were a leak in
the torch body. Preventive action is normally to weld
upon some scrap material until the torch system has been
reheated to evaporate the water condensation. Running
the purge gas to eliminate the condensate may also be
used, but is not as effective in cold weather as the former
suggestion. If the problem continues after the torch has
been reheated, there probably is a leak in the system.
14.5.2 Tooling Quality. The quality of weld tooling
and fixturing can have a significant impact on the quality
of the weldment. Dimensional tolerances and surface finish are generally the two main considerations for tooling
quality. Often, the quality that is required for the tooling
is part specific. Thus, a complex assembly with many
details will often require closer tolerances and a more
elaborate fixture than a simple, noncritical part. For simple welded assemblies, a freehand sketch of the tooling
or fixture on a piece of scratch paper may be adequate.
With a complex assembly, a detailed engineering drawing may be required. Tool “tryout” is often desirable to
ensure that the tooling functions correctly prior to welding of production parts.
14.4.4 Restrictions in the Hoses. Water cooling
hoses may be blocked or pinched, causing the GTAW
torch to overheat. When this occurs, the first thing to
check is that the lines are not pinched or that any heavy
items have not been inadvertently placed upon the hoses
or hose assemblies. Other possibilities for inadequate
coolant flow include ice or foreign particles in the lines,
torch body, or fittings. This cause can be readily checked
by disconnecting the cooling water return line, turning
on the coolant, and observing the flow from the return
line into an open drain or reservoir. If required, the water
cooling system should be cleaned until proper flow is
obtained.
14.6 Filler Material
14.6.1 Filler Metal Control. It is recommended that
filler metals be kept in a controlled storage area. In some
industries, such as nuclear and aerospace, it is common
practice to test each filler lot of material for proper alloy
type and weldability prior to releasing it for storage in
the controlled area. Filler metal containers are always labeled. Additionally, filler metals are generally marked
with a tag, color code, impression stamp or printed label
on each piece of cut wire. Spooled wire is labeled on
each spool. Even with these precautions, filler metals can
become improperly labeled or their identification lost. If
the wrong filler metal identification is suspected, or if the
identification is lost, the materials should be sent to a
qualified testing laboratory to determine its chemical
composition. If the quantity of filler metal does not justify the cost of testing, it should be discarded.
Welders and welding operators must be absolutely
sure that they are using the correct filler metal for each
welding operation. During welding of a component, only
the filler metal specified for the weldment should be
present in the weld booth or weld station. When welding
with that filler metal is complete, the unused filler metal
should be immediately returned to the controlled storage
area. What can happen if such stringent procedures are
not followed is illustrated by the following example. A
welder was having an extremely difficult time joining
14.5 Tools and Fixtures
14.5.1 Construction and Materials. The type of
materials used for tooling and fixtures can be critical to
the quality of GTAW weldments for some metal alloys.
Furthermore, the construction of tooling may be simple
or complex depending upon the application. The following items are critical factors that should be considered in
designing tooling and selecting tooling materials:
(1) Magnetism
(2) Electrical conductivity
(3) Workpiece lead location
(4) Thermal conductivity
(5) Reaction of the tooling materials with base metal;
e.g., copper tooling needs to be chrome or nickel plated
if used for welding cobalt alloys
(6) Melting point relationship
106
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
16 gage (0.06 in. [1.6 mm]) 316 stainless. The weld pool
was out of control. A small amount of the filler seemed
to mix with the molten metal, but most of the filler
“popped” or “jumped” out of the pool. The resultant
weld was very brittle, discolored and contained numerous small cracks and surface porosity. The cause for this
aberrant behavior was that the filler metal rods had lost
their identification and there were mixed filler metals
(stainless steel and titanium) in the container, as revealed
by spectrographic analysis of the some of the filler
metals.
be used to clean aluminum filler metals, but silicon carbide paper is not recommended because silicon carbide
could contaminate aluminum filler metals even though in
both cases, removal of the abrasive from the filler metal
was carried out.
As noted before, the base metals must also be clean.
In the event the weldment requires multiple passes,
cleaning between passes is often required. This can usually be accomplished by vigorously brushing with a
clean wire brush and then wiping. Austenitic stainless
steel brushes are preferred over low alloy or plain carbon
steel varieties. Brushes should not be interchangeably
used on different metals, e.g., a brush used to a clean
steel weldment should not be used on aluminum.
14.6.2 Size and Shape. The size and shape of filler
metals can affect the quality of the weld. Shape is normally not a problem with manual welding as long as the
cross sectional areas are nearly identical. However, with
mechanized or automatic welding the shape can affect
the feeding mechanism or melting efficiency.
With both manual and nonmanual welding, size can
have an adverse effect. In general, if one has trouble
keeping enough filler metal in the molten pool, the size is
too small. Conversely, if adding filler metal causes the
molten pool to freeze or if adequately melting the filler
metal is a problem, the filler wire size is too large.
Consumable inserts, such as rings used in pipe welding, have a large variety of sizes and shapes. Care should
be exercised to ensure that the same size and shape listed
in the WPS is being utilized. Additionally, some insert
shapes allow the entrapment of impurities between the
joint member and the insert, thus causing weld defects
such as inclusions or porosity.
14.7 Design of Welded Assemblies. The design of a
welded assembly can affect the cost of production, assembly quality, ease of weld access, ease of inspection,
manufacturing flow time, and reliability of the welded
assembly in actual use. Unfortunately, in many instances,
by the time an assembly reaches the welding facility, its
design has already been completed. However, the importance of feedback should not be overlooked. If a design
change can make a welded joint more reliable or easier, it
should be reported back to the engineering or design
authority.
Generally, the best weld design is the design with the
least amount of welding! Also, making all the welds in
the flat position is easier and often leads to higher quality
welds than if the welds are made in other positions. Furthermore, the length of the weld joint, the width of the
weld joint, the number of passes, the volume of each
weld, and the number of weld joints should be kept to a
minimum. As with all generalities there will be exceptions. For example, it might be desirable to make a
longer weld in a lightly stressed region than to make a
shorter weld in a highly stressed region.
How design changes and the reduction of the number
of welds in a tank can improve weld quality and minimize distortion is illustrated by the following example.
The original design of an odd shaped tank required the
fabrication of numerous longitudinal welded segments
shaped like a peeled orange segment. Extensive distortion was present and the manufacturing flow time was
felt to be excessive. The design was changed from these
multiple segments to two deep drawn tank ends connected by a circumferential weld on each side of an attachment ring. The total weld length was reduced to 20%
of the original total length. Also, the new assembly design allowed mechanized welding (which increased the
joint quality), eliminated distortion, reduced fit-up time,
increased production quantities, and lowered total cost.
14.6.3 Cleanliness. The cleanliness of filler metals
(and base materials) is paramount to good weld quality.
Welding filler metals must be stored in a clean, contamination-free environment. Aluminum and magnesium alloys are notorious for picking up moisture from the
atmosphere if not kept in a controlled humidity or warm
(often the warming action of a 150 watt light bulb is adequate) environment. Most other GTAW filler metals, because they are normally just bare wires, are not too
susceptible to moisture pick up from the atmosphere.
However, low alloy steel and copper filler alloys can corrode due to humidity, with detrimental effects on weld
quality.
Prior to use, filler metals should be wipe-tested with a
clean cloth moistened with an approved solvent such as
isopropyl alcohol. After wiping, the cloth should show
almost no sign of contamination. In the event contamination is present, corrective measures should be taken.
Chemical cleaning, acid pickling, abrasive cloth cleaning, elevated temperature baking, and shaving have all
been successfully used. Care must be taken to ensure that
the cleaning process does not contaminate the filler
metal. For example, aluminum oxide abrasive paper may
14.7.1 Weld Joint Location. The weld joint locations
should allow easy access by the welder and, whenever
107
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
possible, permit the use of a mechanized or automated
GTAW process. Other factors when considering weld location include stress level, welding sequence, and overall
manufacturing cost. For example, if a complex housing
required tubing to be attached, it might be desirable from
a welding perspective to machine tube stubs onto the
housing so that high quality orbital tube welds could be
made. This design would simplify and likely optimize
the welding operation. On the other hand, the cost of machining the tube stubs integrally with the housing might
well more than offset the additional cost of manually
welding the tubing into orifices via a fillet weld. Thus,
each assembly must be assessed individually. In all cases
the possibility of utilizing mechanized welding for long
production runs should be considered.
When multiple welds are needed, sequencing of the
welds is another factor that must be considered for joint
location. Whenever possible, the sequencing should provide ease of access and yet reduce overall distortion.
can cause a hazardous situation for everyone in the area.
The process of arc welding creates several hazards that
must be guarded against. Useful safety information can
be found in the Owner’s Manual that comes with each
item of welding equipment. More detailed information
can be found in the latest edition of ANSI Z49.1, Safety
in Welding, Cutting, and Allied Processes, (published by
American Welding Society). For mandatory Federal
safety regulations established by the U.S. Labor Department’s Occupational Safety and Health Administration
(OSHA), refer to the latest edition of OSHA Standards
Code of Federal Regulations, Title 29 CFR 1910 (General Industry) available from the Superintendent of
Documents, U.S. Government Printing Office, Washington, DC 20402. Other standards may also apply such as
29 CFR 1915 for use in shipyard fabrication.
15.2 Electrical Shock. Since GTAW is an electrical arc
welding process, welders must be aware of the possibility of electrical shock. Electricity will always take the
path of least resistance. Therefore, it is important that
good connections exist in the entire secondary circuit,
that the workpiece is properly connected to the work lead
of the welding machine, that all cables and their insulation be in good condition, and that all connections are
tight. The welding area should be dry. If there are poor
connections, bare spots on cables, or wet conditions, the
possibility of electrical shock exists. A welder should
never weld while standing in water. If wet working conditions exist, specific safety measures must be taken.
The electrical equipment should be installed and
maintained in accordance with the National Electrical
Code and any state and local codes that apply. Welders or
GTAW operators should never attempt to repair the electrical equipment controlling or providing power for the
GTAW power source. Control boxes should not be
opened. Only trained and qualified electricians should attempt electrical repairs.
14.7.2 Weld Joint Positions. The flat or horizontal
position is the preferred position for all weldments.
These are defined as positions 1G and 2G for groove
welds and 1F and 2F for fillet welds in AWS A3.0. For
manual welding, these positions require less welder skill
than other welding positions. For mechanized welding,
control of power and filler feed are also simpler for flat
or horizontal weldments. Generally, when less skill is
required to perform a weld or when the control of the
weld is simpler, consistently higher quality weldments
are usually the end result.
14.8 Weld Joint Fit-Up. Joint fit-up problems are generally easy to troubleshoot because they are easy to spot. If
the joint has mismatch, if the root opening is incorrect or
highly variable, or if the weld preparation for the joint
has been incorrectly or sloppily done, the weld should
not be started until the fit-up problems have been
corrected. Making a weld on a joint with poor fit-up is
asking for weld quality problems.
15.3 Arc Radiation and Burns. Gas tungsten arc welding results in relatively high levels of visible and ultraviolet light (UV), and infrared radiant energy. Exposure of
uncovered areas of the body to the arc radiation can produce burns similar to sunburn. As exposure time increases, the severity of the burn increases. Even short
periods of exposure (less than a minute) can produce
burns on exposed skin. Screens (or some other suitable
shielding) should be placed around the welding area to
protect visitors and other workers from the arc’s direct
and reflected radiation.
15. Safety
15.1 Hazards. As in any welding process, safety precautions for the GTAW process are very important. There
are many potential hazards common to all arc welding
processes. This section concentrates on potential hazards
associated primarily with the GTAW process, but no attempt has been made to include all hazards resulting
from the misapplication of the process.
All information relating to the safe operation of the
welding equipment and the welding process must be
fully understood before attempting to begin work. A
careless welder who does not observe some simple rules
15.3.1 Eye Protection. The welding arc must never
be viewed with unprotected eyes. Even short exposures
to the arc, which sometimes occur accidentally, can
cause an eye condition known as “flash burn.” Usually
this is not a permanent injury, but may be painful for a
108
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
short time after exposure. The feeling can be described
as having sand in one’s eyes. Sometimes it is possible for
a period of 4–8 hours to pass before a painful sensation
in the eye sets in. Some cases of flash burn may require
treatment by a doctor.
Most industrial locations require the use of safety
glasses. But even if they are not required in some places
of a facility, they are absolutely essential for anyone
working in or passing through an area where welding is
performed.
15.3.2 Clothing. The GTAW process produces fewer
sparks and is considered cleaner than many welding
processes. Thus, lighter clothing is often worn. However,
clothing should be made of a tightly woven flameretardant material. Coverage of all exposed skin not protected by a welding hood is required to prevent radiation
burning. Figure 65 shows a welder equipped for light
duty welding. Welding out of position or on material
prone to producing sparks may require leather chaps,
sleeves, and aprons worn over light clothes for additional
protection. Clothing and shoes must be kept free of oil
and grease or other flammable materials. Protective, heat
resistant, nonflammable gloves (typically leather) should
be worn to protect the hands and wrists.
CAUTION
Continued flash burns could cause permanent eye
damage.
The welder should always be required to wear a welding helmet equipped with the proper shade lens for the
work being done. Welding lenses are not simply colored
glass, but are special lenses which screen out almost
100% of the infrared and ultraviolet rays. Lenses are
manufactured in various shades designated by a shade
number, and the higher the shade number, the darker the
lens. The choice of a shade may vary depending upon a
person’s sensitivity of eyesight and the welding variables. Generally speaking, the welding current used determines the lens shade needed. The higher the current,
the more need there is for a darker shade lens. Table 22
lists lens shades for various welding currents. A number
10 lens is suitable for most GTAW applications. Care
should be taken when using arc-activated lenses to assure
proper shade setting and speed of operation before welding. A low battery can result in the malfunction of such
units and can result in inappropriate exposure to the arc.
Additional safety rules and lens recommendations can be
found in the AWS approved ANSI Z49.1, Safety in
Welding, Cutting, and Allied Processes.
Flash burns of the eyes may occur to people who are
not welding. Persons passing by an area where welding
is being done could possibly get flash burn from reflected radiation. Therefore, it is recommended that all
people in the welding area wear approved, tinted safety
glasses that filter out UV rays.
15.4 Welding Environment. Similar to many other arc
welding processes, GTAW produces UV and infrared radiation, heat, smoke, and fumes which enter the area
where welding is performed. Natural and exhaust ventilation of the weld area is normally adequate for most
GTAW operations. However, exhaust hoods or other devices are sometimes used for local fume removal, when
needed.
In certain applications, additional precautions must be
taken. Metals that have plating, coatings, paint or other
materials near to the arc area may give off smoke and
fumes during welding. Health hazards, especially to the
lungs, may exist from these fumes. The physiological effects of the fumes produced will vary with the metal or
coating involved. Exposure must be evaluated on an individual fume exposure basis. The ventilation and protection requirements listed in ANSI Z49.1 should be
followed.
15.4.1 Ozone. The ultraviolet light emitted by the
GTAW arc acts on the oxygen in the surrounding atmosphere to produce ozone, a gas with a very pungent distinctive odor. The amount produced will depend upon the
intensity and the wavelength of the ultraviolet energy, the
humidity, the amount of screening afforded by any welding fumes, and other factors. The ozone concentration
will generally be increased with an increase in welding
current, with the use of argon as the shielding gas, and
when welding highly reflective metals such as aluminum. If the ozone cannot be reduced to a safe level by
ventilation or process variations, it will be necessary to
supply fresh air to the welder either with an air supplied
respirator or by other means.
Ozone exposures during typical welding operations
are generally below accepted thresholds. However,
Table 22
Guide for Shade Numbers
Arc Current, (A)
Minimum Shade
Suggested Shade(1)
8
8
10
11
10
12
14
14
Less than 50
50 to 150
150 to 500
500 to 1000
Notes:
(1) As a rule of thumb, start with a shade that is too dark to see the weld
zone. Then go to a lighter shade which gives sufficient view of the
weld zone without going below the minimum.
Reference: See latest edition of ANSI Z49.1, Safety in Welding, Cutting,
and Allied Processes.
109
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
certain conditions, such as welding in confined spaces or
on highly reflective surfaces using argon-rich gases, may
result in exposures exceeding published limits.
cylinder’s weight and velocity could cause serious injury
or even a fatal accident. It is imperative that cylinders are
securely fastened at all times (while on location or while
being transported in suitable cylinder carts). Chains are
usually used to secure a cylinder to a wall or cylinder
cart.
15.4.2 Chlorinated Hydrocarbons. Decomposition
products of chlorinated hydrocarbons can include toxic
gases such as phosgene, hydrogen chloride, and chlorine.
These products are injurious to the lungs, upper respiratory system, eyes and skin. Experimental evidence has
shown that chlorinated hydrocarbon vapors in the vicinity of an arc (even though not in direct contact with the
arc) decompose rapidly. The decomposition is caused by
the ultraviolet radiation rather than by the high temperature of the arc. Although the concentration of chlorinated
hydrocarbon vapors may be too low to be detectable by
the sense of smell, welding in areas containing chlorinated hydrocarbon vapors can produce excessive concentrations of these toxic gases. Greater decomposition is
produced by argon than by helium because of the greater
radiation intensity when using argon.
15.8 Fires and Explosions. Hot slag, sparks, and arc
radiation act as a source of ignition and burns. Fires and
explosions are hazards that can exist in a welding area.
The welding area must be kept free of flammable, volatile, or explosive materials. The welder or operator
should wear flame-retardant, appropriate clothing for the
operation. Welding should never be performed on sealed
containers or containers that have held combustibles.
Welding should not be attempted in enclosed areas, such
as the inside of tanks, without extra-special precautions
including lookouts and training in emergency procedures
in accordance with ANSI Z49.1. Workers should be
familiar with fire prevention and fire and burn protection
measures.
15.5 Oxygen Deficiency. Shielding gases can displace
oxygen in enclosed and confined spaces. This can result
in simple asphyxiation without warning. Argon and helium are commonly used shielding gases in GTAW.
Argon (since it is heavier than air) settles near the bottom
of confined spaces, while helium and nitrogen (since
they are lighter than air) rise to the top of confined
spaces. These colorless, odorless and tasteless gases cannot be detected by the human senses at concentrations
normally present in welding operations. An atmosphere
with a diminished oxygen level can cause dizziness, unconsciousness, or even death. Tanks and confined spaces
should always be checked for oxygen content prior to entry. The ventilation requirements set forth in the latest
edition of ANSI Z49.1 should be followed when welding
or working in confined areas.
15.9 Common Sense. It is very important to be fully
trained in the use of the welding equipment before attempting to use it. If unsure about any aspect of the operation, the welder or operator should speak first with the
welding supervisor. Safety is an important factor not
only for oneself, but also for everyone in the vicinity. It
can be said that common sense is the most important tool
a welder can bring to the welding area. Common sense
tells us we must respect the basic safety steps which must
be taken to avoid both personal injury and injury to a fellow worker.
15.10 Grinding Dust.100, 101, 102, 103, 104, 105 The grinding
(sharpening) of tungsten electrodes generates tungsten
metal dust. This dust may also contain small amounts of
oxides like zirconia, ceria, lanthana and/or thoria. Dust
generated by grinding can be considered a health hazard
15.6 Noise. Normal GTAW operations do not exceed
noise level requirements as specified by OSHA. However, associated activities (e.g., grinding, sand blasting)
may produce excessive noise levels. Exposed workers
should wear properly fitted ear protection in such cases
because exposure to excessive noise levels for extended
periods of time may result in hearing impairment.
100. “Thoriated Tungsten Electrodes Studied for Effects on
Welders’ Health,” Welding Journal, Vol. 73, No. 5, May 1994,
pp. 88–89.
101. Vinzents, P., Poulsen, O. M., et al., 1994. “Cancer Risk
and Thoriated Welding Electrodes,” Occupational Hygiene,
Vol. 1, No. 1, 1994 pp. 27–33.
102. McElearny, N. and Irvine, D., 1993. “A Study of Thorium
Exposure During Tungsten Inert Gas (TIG) Welding in an Airline Engineering Population,” Journal of Occupational Medicine, Vol. 35, No. 7, July 1993, pp. 707–711.
103. “Practical TIG (GTA) Welding,” Muncaster, P. W., 1991,
p. 25, Abington Publishing, ISBN 1855730200.
104. MSDS sheets, tungsten mfg.
105. Campbell, R. D. and LaCoursiere, E. J., 1995. “A Guide to
the Use of Tungsten Electrodes for GTA Welding.” Welding
Journal, Vol. 74, No. 1, Jan. 1995, pp. 39–45.
15.7 Safe Handling of Cylinders.99 Regardless of the
content, pressurized cylinders must at all times be handled with great care. Shielding gases such as argon and
helium are nonflammable and nonexplosive. However, a
broken cylinder valve could release the content under extremely high pressure, which could cause the cylinder to
be hurled about at dangerously high speeds. A damaged
99. For more information, see CGA Pamphlet P-1, Safe Handling of Compressed Gases in Containers.
110
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
and most health authorities recommend that all metal
grinding machines provide transparent eye shields, dust
extractors and filters. Dust produced by tungsten grinding should never be inhaled by the person doing the
grinding or by adjacent personnel. Metal dust can cause
pulmonary illness over long periods of inhalation, so it is
important to protect oneself. Good shop practice and
common sense should be used for grinding anything.
Wearing a full-face shield and safety glasses fitted with
side shields, and not wearing loose fitting clothing that
could get caught in the machine are also good practices.
If electrode-grinding dust might be inhaled, special precautions relative to ventilation should be considered. A
vacuum or exhaust system should be used when grinding
electrode tips. Electrode-grinding dust must not be inhaled. The user should consult the appropriate safety
procedures, the manufacturer’s suggested procedures,
and all internal company safety requirements.
111
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
This page is intentionally blank.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Nonmandatory Annexes
Annex A
Guidelines for Preparation of Technical Inquiries for
AWS Technical Committees
(This Annex is not a part of AWS C5.5/C5.5M-2003, Recommended Practices for
Gas Tungsten Arc Welding, but is included for informational purposes only.)
A1. Introduction
with the edition of the standard that contains the provisions or that the Inquirer is addressing.
The AWS Board of Directors has adopted a policy
whereby all official interpretations of AWS standards
will be handled in a formal manner. Under that policy, all
interpretations are made by the committee that is responsible for the standard. Official communication concerning an interpretation is through the AWS staff member
who works with that committee. The policy requires that
all requests for an interpretation be submitted in writing.
Such requests will be handled as expeditiously as possible but due to the complexity of the work and the procedures that must be followed, some interpretations may
require considerable time.
A2.2 Purpose of the Inquiry. The purpose of the inquiry must be stated in this portion of the inquiry. The
purpose can be either to obtain an interpretation of a
standard requirement, or to request the revision of a particular provision in the standard.
A2.3 Content of the Inquiry. The inquiry should be
concise, yet complete, to enable the committee to quickly
and fully understand the point of the inquiry. Sketches
should be used when appropriate and all paragraphs, figures, and tables (or the Annex), which bear on the inquiry must be cited. If the point of the inquiry is to obtain
a revision of the standard, the inquiry must provide technical justification for that revision.
A2. Procedure
A2.4 Proposed Reply. The inquirer should, as a proposed reply, state an interpretation of the provision that
is the point of the inquiry, or the wording for a proposed
revision, if that is what inquirer seeks.
All inquiries must be directed to:
Managing Director, Technical Services
American Welding Society
550 N.W. LeJeune Road
Miami, FL 33126
A3. Interpretation of Provisions of
the Standard
All inquiries must contain the name, address, and affiliation of the inquirer, and they must provide enough
information for the committee to fully understand the
point of concern in the inquiry. Where that point is not
clearly defined, the inquiry will be returned for clarification. For efficient handling, all inquiries should be typewritten and should also be in the format used here.
Interpretations of provisions of the standard are made
by the relevant AWS Technical Committee. The secretary of the committee refers all inquiries to the chairman
of the particular subcommittee that has jurisdiction over
the portion of the standard addressed by the inquiry. The
subcommittee reviews the inquiry and the proposed reply
to determine what the response to the inquiry should be.
Following the subcommittee’s development of the response, the inquiry and the response are presented to the
entire committee for review and approval. Upon ap-
A2.1 Scope. Each inquiry must address one single provision of the standard, unless the point of the inquiry
involves two or more interrelated provisions. That provision must be identified in the scope of the inquiry, along
113
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
proval by the committee, the interpretation will be an official interpretation of the Society, and the secretary will
transmit the response to the inquirer and to the Welding
Journal for publication.
tained only through a written request. The Headquarters
staff cannot provide consulting services. The staff can,
however, refer a caller to any of those consultants whose
names are on file at AWS Headquarters.
A4. Publication of Interpretations
A6. The AWS Technical Committee
All official interpretations will appear in the Welding
Journal.
The activities of AWS Technical Committees regarding interpretations are limited strictly to the Interpretation
of provisions of standards prepared by the committee or
to consideration of revisions to existing provisions on the
basis of new data or technology. Neither the committee
nor the staff is in a position to offer interpretive or consulting services on: (1) specific engineering problems; or
(2) requirements of standards applied to fabrications outside the scope of the document or points not specifically
covered by the standard. In such cases, the inquirer
should seek assistance from a competent engineer experienced in the particular field of interest.
A5. Telephone Inquiries
Telephone inquiries to AWS Headquarters concerning AWS Standards should be limited to questions of a
general nature or to matters directly related to the use of
the standard. The Board of Directors’ policy requires that
all AWS staff members respond to a telephone request
for an official interpretation of any AWS standard with
the information that such an interpretation can be ob-
114
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
Annex B
Suggested Reading List and Other References
(This Annex is not a part of AWS C5.5/C5.5M-2003, Recommended Practices for
Gas Tungsten Arc Welding, but is included for informational purposes only.)
(1) Bittence, J. C., “Welding the Advanced Alloys”
Advanced Materials and Processes, 35–39, Metal
Progress; December 1987.
(2) Heiple, C. R., et al., “Surface Active Elements Effects on the Shape of GTA, Laser, and Electron Beam
Welds.” Welding Journal 62(3): 72s-77s; March 1983.
(3) Katoh, M. and Ken, H. W., “Investigation of
Heat-Affected Zone Cracking of GTA Welds of Al-MgSi Alloys using the Varestraint Test.” Welding Journal
66(12): 360s; December 1987.
(4) Kelly, T. J., “Rene 220C—The New, Weldable
Investment Cast Superalloy.” Welding Journal, 69(11):
422-s–430-s; November 1990.
(5) Kujanpaa, V. P., et al., “Role of Shielding Gases
in Flaw Formation in GTAW of Stainless Steel Strips.”
Welding Journal 63(5): 151s-155s; May 1984.
(6) Linnert, G. E., “Welding Characteristics of Stainless Steels.” Metals Engineering Quarterly 1-15; November 1967.
(7) NASA Tech Brief MFS-27121, “Microstructure
and Weld Cracking in Inconel 718.” Marshall Space
Flight Center, Alabama; March 1979.
(8) Patterson, R. A., et al., “Discontinuities Formed in
Inconel GTA Welds.” Welding Journal, 65(1): 19-s–25s; January 1987.
(9) Sullivan, R. P., “Fusion Welding of Stainless
Steels.” ASM Metals Engineering Quarterly, 16-41;
November 1967.
(10) Kato, S. and Tanabe, S., “High Speed Welding of
0.5mm Thickness Alloy Sheets using Pulsed TIG Welding.” Welding International (7): 602–608; 1988.
(11) Prager, M. and Shira, C. S., “Welding of
Precipitation-Hardening Nickel-Base Alloys.” Welding
Research Council Bulletin, 128; 1968.
(12) Yeniscavich, W., “Chapter 18—Joining.” Superalloys, II; 1987.
(13) Burgardt, J. and Campbell, R. D., “Chemistry
Effects on Stainless Steel Weld Penetration” Key Engineering Materials, Vols. 69 & 70 (1992) pp. 379–416.
(14) Shirali, A. A. and Mills, K. C., “The Effect of
Welding Parameters on Penetration in GTA Welds,”
Welding Journal, 72(7), July 1993.
(15) Anik, S. and Dorn, L., “Metallophysical Processes in
the Welding of Copper and Copper Alloys—Welding Methods,” Welding and Cutting, Vol. 9, 1988 p. E139–E143.
115
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
This page is intentionally blank.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
AWS C5.5/C5.5M:2003
List of AWS Documents on Arc Welding and Arc Cutting
AWS Designation
Title
C5.1
Recommended Practices for Plasma Arc Welding
C5.2
Recommended Practices for Plasma Arc Cutting
C5.3
Recommended Practices for Air Carbon Arc Gouging and Cutting
C5.4
Recommended Practices for Stud Welding
C5.6
Recommended Practices for Gas Metal Arc Welding
C5.7
Recommended Practices for Electrogas Welding
C5.10
Recommended Practices for Shielding Gases for Welding and Plasma Arc Cutting
For ordering information, contact Global Engineering Documents, an Information Services Handling (IHS) Group company, 15 Inverness Way East, Englewood, Colorado 80112-5776; telephones (800) 854-7179, (303) 397-7956; fax (303)
397-2740; Internet: www.global.ihs.com.
117
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale
This page is intentionally blank.
Copyright American Welding Society
Provided by IHS under license with AWS
No reproduction or networking permitted without license from IHS
Not for Resale