Trimteck Valve Training Module 3 - Severe Service Applications & Solutions

Trimteck-Optimux Control Valves
Analysis of Severe Service Applications & Technologies
Training Module 3
About Trimteck
Trimteck is a family-owned American company with 15 years of experience in
engineering, manufacturing, and marketing high-quality, cost-effective flow control
solutions for critical processes. Our products are currently helping customers safely
improve quality, optimize throughput, and reduce costs and emissions across an array
of industries in more than 50 countries. Our applications engineers and certified
representatives are committed to personalized customer service.
Trimteck manufactures a comprehensive line of Optimux control valves – and a variety
of actuators, positioners, severe service trims, and other accessories – that our
applications engineers and representatives use to solve the most complex flow,
pressure, and temperature control problems quickly and economically.
Welcome to Trimteck.
-1-
Value Proposition
As Trimteck grows, we are increasingly honing our value proposition to express
that we are an innovative, agile organization that competitively offers a full
control valve line of exceptional quality and proven design
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Agenda
I. Understanding Severe Service Problems
II. Generic Guidelines for Valve Selection
III. Specific Guidelines for Severe Service Valve Selection
-3-
Understanding Severe Service Problems
15% of valves are responsible for 85% of valve problems in any
given industrial plant; and using the wrong valve in a severe
service application can lead to costly premature failures
-4-
What Constitutes a Problem Valve?
In general, there are three major categories of problems that can be predicted and
addressed while sizing and specifying a control valve
Problem
Factors
1. Cavitation & Flashing
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•
•
•
•
•
•
•
•
Excessive Fluid Energy Along Flow Path
Inadequacies in Actuation System
Pressure Drop
Velocity
Flow Rate
Trim Selection
Seat Leakage
Consistency & Composition of Fluid
Time of Exposure
•
•
Consistency & Composition of Fluid
Incorrect Material Selection
2. Noise & Vibration
3. Corrosion & Erosion
-5-
Background: Fluid Flow & Pressure Recovery
Fluid Flow and Pressure
Recovery in a Control Valve
P1
Low Recovery
Pressure
P2
High Recovery
Pvc
Vena Contracta
Valve
Inlet
Trim
Inlet
Trim
Outlet
-6-
Valve
Outlet
Cavitation Explained
Cavitation and flashing in control valves occur only with liquid media, and the
principal factors responsible are fluid velocity and pressure drop.
If upstream pressure is just above the vapor pressure, then the pressure may drop
below the vapor pressure as the fluid flows through the valve.
Cavitation will occur if the pressure recovers downstream of the valve to a
pressure that is once again above the vapor pressure.
Velocity
Pressure
-7-
Background: Cavitating & Flashing Flow
Liquid Flow Regimes in a Control Valve
P1
Pressure
Pv
Cavitating Flow
P2
Vapor Pressure
Flashing Flow
Pvc
Vena Contracta
Valve
Inlet
Trim
Inlet
Trim
Outlet
Valve
Outlet
-8-
Flow Path
Cavitation Damage
Cavitation damage is a form of hyper-erosion that can destroy both control valves
and piping, which can result in unacceptable process failures.
The vapor bubbles created as a result of a pressure drop will implode – nucleate,
grow, collapse, and rebound – as the vapor returns to liquid form.
The implosion of vapor bubbles in the cavitation phenomenon inflicts damage in
the form of small pits in the metal, which cumulatively wear away surfaces.
Valve Plug with Cavitation Damage
Implosion of Vapor Bubbles on Surfaces
-9-
Flashing Explained
Similarly to cavitation, if upstream pressure is just above the vapor pressure, then
the pressure might drop below the vapor pressure as the fluid flows through the
valve.
Unlike cavitation, however, flashing will occur if the pressure does not recover
downstream of the valve, but rather remains below the vapor pressure.
- 10 -
Background: Cavitating & Flashing Flow
Liquid Flow Regimes in a Control Valve
P1
Pressure
Pv
Cavitating Flow
P2
Vapor Pressure
Flashing Flow
Pvc
Vena Contracta
Valve
Inlet
Trim
Inlet
Trim
Outlet
Valve
Outlet
- 11 -
Flow Path
Flashing Damage
In flashing service, the pressure drop will result in the process flashing from a liquid form to
a gaseous form, carrying with it the liquid droplets at high velocity through the valve trim
and into the downstream piping.
Flashing damage is characterized by scalloping of the metal parts within the valve.
- 12 -
Noise & Vibration Explained
As pressure drop is taken in a control valve, most of the resultant energy is lost as heat and
the remainder is converted to noise.
In liquid applications, both cavitation and flashing tend to cause hydrodynamic noise,
however, in gaseous applications – gas or steam – a sudden pressure drop and high
velocity cause turbulence that results in aerodynamic noise.
Aerodynamic noise is a problem not only because of the noise pollution and possible
damage to people within earshot, but because it indicates that there is turbulence and
vibration in the valve and the downstream piping, which can cause physical damage to
equipment.
- 13 -
Vibration Damage
Shockwaves and turbulence, often caused by the control valves themselves,
sometimes create vibration in the pipeline.
If the plug stem is not rigid (i.e. is a two-piece threaded stem), properly aligned,
and well-actuated, the plug could oscillate around the seat and eventually crack
the stem.
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Factors Explained
- 15 -
Corrosion & Erosion Explained
Corrosion is the deterioration of a material resulting from a chemical or
electrochemical reaction with its environment, such as a trim component in
contact with the process fluid.
General corrosion affects the entire surface of the exposed material uniformly,
while localized corrosion can manifest itself by pits and cracking in specific
locations.
In control valves, erosion is generally defined as the wearing away of a material by
any of many severe services: dirty process, cavitation, and flashing. In this
discussion, we will limit our analysis of erosion to that caused by a dirty process
– or particulates in suspension.
There are cases when corrosion and erosion combine to cause significant damage.
- 16 -
Corrosion Damage
Valve Stem and Yoke Corrosion
Valve Plug Corrosion
- 17 -
Agenda
I. Understanding Severe Service Problems
II. Generic Guidelines for Valve Selection
III. Specific Guidelines for Severe Service Valve Selection
- 18 -
Generic Requirements for Valve Selection
The first step in combating severe service applications is selecting the correct
valve for the service.
Generic Selection Requirements Include:
 Valve Coefficient
 Flow Characteristic
 Rangeability
 Shutoff/Leakage Class
 Body Materials & Style
 Trim Materials & Design
 Soft Goods Materials
Optimux OpGL Globe Control Valve
- 19 -
Valve Coefficients
The measurement commonly applied to valves is the valve coefficient (CV) - also
referred to as the flow coefficient - which is used to determine the valve size that
will best allow the valve to pass the required flow rate while providing control of
the process fluid
One CV is defined as one U.S. gallon (3.78 liters) of 60°F (16°C) water that flows
through an opening during 1 minute with a 1- psi (0.1-bar) pressure drop
CV = Flow coefficient
F = Flow rate (US GPM).
SG = Specific Gravity fluid (Water = 1).
ΔP = Pressure drop (psi).
- 20 -
OpGL Trim – Flow Characteristics
Each valve has a flow characteristic, which describes the relationship between the
valve coefficient (CV) and the valve stroke – as a valve opens, the flow
characteristic—which is inherent to the design of the selected valve—allows a
certain amount of flow through the valve at a particular percentage of the stroke,
which allows the valve to control the flow in a predictable manner
The three most common types of flow characteristics are equal percentage, linear,
and quick-open
- 21 -
Flow Characteristics Continued
Two rules of thumb for choosing the right flow characteristic:
1. If most of the pressure drop is taken through the valve and the upstream
pressure is constant, a linear characteristic will provide better control
2. If the piping and downstream equipment cause significant resistance to the
system, equal percentage will provide better control
Control Valve Pressure Drop
Recommended Inherent Flow
Characteristic
Constant ΔP
Linear
Decreasing ΔP with increasing load: ΔP at maximum
load >20% of minimum load ΔP
Linear
Decreasing ΔP with increasing load: ΔP at maximum
load <20% of minimum load ΔP
Equal Percentage
Increasing ΔP with increasing load: ΔP at maximum
load <200% of minimum load ΔP
Linear
Increasing ΔP with increasing load: ΔP at maximum
load >200% of minimum load ΔP
Quick Open
- 22 -
Rangeability
Rangeability is the ratio of maximum to minimum flow that can be acted upon by a
control valve after receiving a signal from a controller
High rangeability allows a valve to control flow from large to small flows, and it is
imperative to select as broad of rangeability as possible in cavitating
applications.
Rangeability is affected by three factors:
1. Valve geometry – inherent rangeability due to the design of the body and the
valve plug
2. Seat leakage – excessive seat leakage can cause instability as the valve lifts off
of the seat
3. Actuator – diaphragm actuators are seldom accurate at less than 5% of the valve
opening, whereas piston-cylinder actuators can provide control within 1% of valve
lift due to the presence of air in two chambers
- 23 -
Shutoff Requirements
Industry standards regarding the amount of permissible leakage of the process
fluid through a valve’s seat.
Leakage Class
Designation
Maximum
Allowable
Leakage
Test Medium
Test Pressure
Test Procedure
Class I
N/A
N/A
N/A
No Test
Class II
0.5% of rated
capacity
Air or water at 50
- 125o F(10 52oC)
Lower of 45 - 60 psig or
maximum operating
differential
Lower of 45 - 60 psig or
maximum operating
differential
Class III
0.1% of rated
capacity
As above
As above
As above
Class IV
0.01% of rated
capacity
As above
As above
As above
Class V
0.0005 ml per
minute of water
per inch of port
diameter per psi
differential
Water at 50
to125oF (10 to
52oC)
Maximum service
pressure drop across
valve plug not to exceed
ANSI body rating
Maximum service
pressure drop across
valve plug not to exceed
ANSI body rating
Class VI
Not to exceed
Class VI standard
per port diameter
Air or nitrogen at
50 to 125o F (10
to 52oC)
50 psig or max rated
differential pressure
across valve plug
whichever is lower
Actuator should be
adjusted to operating
conditions specified with
full normal closing thrust
applied to valve plug seal
- 24 -
Shutoff Requirements Continued
In severe service applications, tight
shutoff is imperative and an actuator
that provides the appropriate seat load
is necessary.
Furthermore, when pneumatic actuation
is required, a piston-cylinder actuator
with accessories for velocity control will
provide the end-user with more accurate
control of the process and more thrust
for tighter shutoff.
Trimteck-Optimux Anti-Surge Valve with
OpTK Piston Cylinder Actuator
- 25 -
Body Materials
Common practice dictates that the end-user specify the body material, especially
with special or severe service valves
General service valves are specified with commonly found materials to match the
pipe material
Standard Materials
 Carbon Steel
 Stainless Steel
 Chrome-moly
A Word on Investment Casting …
Control valve bodies are either cast, forged, or machined from bar stock, with
standard sand casting as the most commonplace method
Trimteck elects to use an advanced investment casting method as its
standard for control valve bodies between .5” and 4”
Investment casting offers the following benefits:
Special Alloys
 Hastelloy B and C
 Titanium
 Monel
 Bronze
 Consistent and repetitive close tolerances
 Superior integrity and no porosity
 Fatigue performance equal to that of forgings
 Minimal need for machining
- 26 -
Trim Materials
Valve parts – body, bonnet, bonnet bolting, plug, ball, disk, wedge, and/or drainage
plug – exposed to pressure, process fluid, corrosion, and other effects of the
service are required by regulation to be manufactured from approved metals
In applications requiring elevated material hardness levels and resistance to
corrosion and abrasion, Trimteck has pioneered the use of CVD-5B
Trim Material Characteristics
- 27 -
Gaskets
A gasket is a malleable material, which can be either soft or hard, that is inserted
between two parts to prevent leakage between that joint
Common Gasket Materials and Types
Type
Gasket
Material
Max Temp
(oF/oC)
Min Temp
(oF/oC)
Max Pressure
(psi/bars)
Flat
Virgin PTFE
350/175
-200/-130
6000 – 1000 psi
415 – 70 bar
Flat
Reinforced
PTFE
450/230
-200/-130
6000 – 500 pis
415 – 35 bar
Flat
CTFE
200/95
-423/-250
6000 – 500 psi
415 – 35 bar
Flat
FEP
400/205
-423/-250
6000 – 500 psi
415 – 35 bar
Spiralwound
AFG
1500/815
-20/-30
6250 psi
430 bar
Spiralwound
316SS/PTF
E
350/176
-200/-130
6000 – 500 psi
415 – 35 bar
Spiralwound
316/Graphit
e
1500/815
-423/-250
6250 psi
430 bar
Hollow Oring
Inconel X750
1500/815
-20/-30
15000 psi
1035 bar
- 28 -
Agenda
I. Understanding Severe Service Problems
II. Generic Guidelines for Valve Selection
III. Specific Guidelines for Severe Service Valve Selection
- 29 -
Specific Requirements for Severe Service Valve Selection
The next step in combating severe service applications is to control for the
following elements:
Problem
Requirements
1. Cavitation & Flashing
•
Control Velocity:
•
2. Noise & Vibration
3. Corrosion & Erosion
•
Liquids: Inlet shouldn’t exceed 60
ft/s (18 m/s); Outlet shouldn’t
exceed 100 ft/s (30 m/s)
Gases: Trim exit shouldn’t exceed
head velocity of 70 psi (480 kPa)
•
Stage Pressure Reduction
•
Reduce Noise to 85 dBa at 3 ft (1m)
from the valve (un-insulated)
•
Ensure appropriate material selection
•
Examine Fluid Composition
•
Ensure appropriate material selection
- 30 -
Severe Service Solutions by Technology
In order to solve the various valve problems discussed in Section I, differing
methods and technologies exist; all involve one or more of the following:
 Utilization of low recovery trim packages, which break
down the mass flow into a multiplicity of small flow
streams
 Introduction of multi-stage pressure-reducing trims,
which create a torturous path to further reduce velocity,
pressure, and energy levels
 Optimization of actuation and flow direction to take
further advantage of the design mechanics
 Selection of appropriate materials, some of which are
more resistant to cavitation, flashing, erosion, and
corrosion than others
- 31 -
Sigma (σ): The Cavitation Index
The most widely-accepted and precise cavitation index used to quantify and
predict cavitation in control valves is Sigma (σ).
Simply put, Sigma is the ratio of the potential for resisting formation of vapor
bubbles to the potential for causing formation of vapor bubbles.
- 32 -
Controlling Mild Cavitation: 1.5 < σ < 1.7
When mild cavitation is present in a process, specifying a hardened single-stage
low recovery trim package may be sufficient.
Instead of attempting to eliminate the cavitation, a single-stage trim uses mutual
impingement technology to force the vapor bubbles to collapse against
themselves in the center of the valve gallery – and prevents them from causing
damage to critical metal trim or body components
Mutual Impingement of Vapor Bubbles
Trimteck ST-1 Anti-Cavitation Trim
- 33 -
Controlling Moderate to Severe Cavitation: 1.0 < σ < 1.5
In applications with more severe cavitation, the ideal solution is to reduce pressure
gradually from the trim inlet to the trim outlet.
By staging pressure reduction, the trim can prevent the process pressure from
dipping below the vapor pressure – thereby preventing the formation of the
damaging vapor bubbles altogether.
Liquid Flow through a Four-Stage
Pressure Reducing Trim
Trimteck-Optimux ST-2 Multi-Stage Anti Cavitation Trim
- 34 -
Effects of a Staged Pressure Reducing Trim
Staged Pressure Drop through a Control Valve
Three Stage
Low Recovery
Valve Trim
P1
1
2
3
Pressure
Pv
P2
Vapor Pressure
Pvc
Vena Contracta
Valve
Inlet
Trim
Inlet
Trim
Outlet
Valve
Outlet
- 35 -
Flow Path
Controlling Flashing: σ < 1.0
No matter how many pressure stages are
introduced into a valve, in flashing service
the pressure drop will result in the liquid
flashing from liquid form to a gaseous form
– carrying with it erosive water droplets at
high velocity.
Therefore, if flashing is present in a service,
then the damaging effects must be
controlled by displacing the erosion to
non-critical components in the system.
One way to do this is with a hardened
venturi-style seat in an angle-body valve,
which will displace the effects of the
flashing downstream of the valve.
Trimteck-Optimux ST-5 Venturi Seat Trim
for Flashing Service
- 36 -
Controlling Aerodynamic Noise & Vibration
Similar to cavitating applications, the ideal solution for noise abatement is to
reduce pressure gradually from the trim inlet to the trim outlet. By staging
pressure reduction, the gas velocity and effects of expansion are reduced and
noise is abated.
To reduce the effects of vibration on valve equipment, select a robust single-piece
plug, which is guided in the bonnet as opposed to within the cage.
Multi-Stage Noise Abatement Trim
- 37 -
Trimteck-Optimux ST-3 Multi-Stage
Noise Abatement Trim
Controlling Corrosion & Erosion
Some materials are inherently more resistant to corrosion than other materials.
Alloys containing chromium get their corrosion resistance from a passive oxide
layer on their surface, which acts as a barrier to further oxidation or corrosion.
Most stainless steel and nickel alloys rely on this layer for their corrosion
resistance.
316 Stainless Steel exhibits this type of protective film, and most control valve trim
is manufactured from this material as a standard. In order to achieve increased
protection from corrosion, the amount of nickel in the alloy can be increased.
For example nickel alloy C, commonly known by the Haynes International
trademark Hastelloy® C, exhibits excellent resistance to sulfuric, hydrochloric,
and organic acids as well as ammonia, dry chlorine, and hydrogen sulfide. Nickel
alloy 625, commonly known by the Special Metals trademark Inconel® 625, also
has high corrosion resistance in a wide range of environments, and is commonly
specified in the oil and gas industry for resistance to pitting, crevice corrosion,
and SCC caused by high chloride levels, as well as resistance to sulfide stress
cracking.
- 38 -
Controlling Corrosion & Erosion
In applications requiring elevated material hardness levels and resistance to
corrosion and abrasion, Trimteck has pioneered the use of CVD-5B
CVD-5B is a chemical vapor diffusion process utilizing a hard wear-resistant metal
mesh that deposits itself into the substrate material providing a Rockwell
Hardness level of 72.
Trim Material Characteristics
- 39 -
Trimteck’s Severe Service Philosophy
Severe service applications vary in degree of severity, so without over-engineering,
Trimteck offers its customers timely, cost-effective products to enhance
performance while driving down operating costs
Our rationale is simple: invest in a reasonably-priced custom-engineered solution
and enjoy extended performance combined with a dramatic reduction in
operation and maintenance costs caused by failures and untimely shutdowns
- 40 -
Thank you for your attention, and we hope you will give
Trimteck the opportunity to solve your severe service
applications.