AssesmentofHDPECorrugatedPipesUsedinMiningApplicationsandtheirCompliancewithSpecifications-1

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/283513305
Assessment of HDPE corrugated pipes used in mining applications and their
compliance with specifications
Conference Paper · September 2015
CITATIONS
READS
0
596
3 authors, including:
Mario Paredes
TRI Environmental Inc.
22 PUBLICATIONS 141 CITATIONS
SEE PROFILE
All content following this page was uploaded by Mario Paredes on 06 November 2015.
The user has requested enhancement of the downloaded file.
Proceedings of Heap Leach Solutions, 2015
September 14-16, 2015, Reno, Nevada, USA
Published by InfoMine, © 2015 InfoMine, ISBN: 978-0-9917905-8-6
Assessment of HDPE corrugated pipes used in
mining applications and their compliance with
specifications
Richard W. Thomas, TRI/Environmental, Inc., USA
Mario Paredes, PE TRI/Environmental Inc., USA
David Cuttino, TRI/Environmental, Inc., USA
Abstract
Samples of HDPE Corrugated Pipe were collected from North America, South America, and the United
Kingdom. Each of the dozen samples was characterized by a series of resin and pipe tests. The results
were compared to the requirements found in ASTM Standard Specifications F2986, “Standard
Specification for Corrugated Polyethylene Pipe and Fittings for Mine Leachate Applications,” and F2987,
“Standard Specification for Corrugated Polyethylene Pipe and Fittings for Mine Heap Leach Aeration
Applications.”
Only two of the twelve samples met all of the requirements found in these ASTM standards.
Additionally, five samples contained significant amounts of polypropylene, which indicates the presence
of post-consumer recycled HDPE and two of these also had about 10% added filler. Of the twelve
samples, 58% failed to achieve the minimum resistance to cracking criteria of 24 hours by the NCLS
stress crack test (ASTM F2136). This paper presents all the results obtained and discusses the potential
implications for the long-term performance of the different pipe products in mining applications,
particularly in heap leach pads.
Introduction
Corrugated HDPE pipe plays an important role in heap leach pad mining applications. Since it may
experience some loads or strains from the very thick ore overburden, and exposure to harsh chemicals like
concentrated sulfuric acid, it should be made with consistent high quality to perform as intended. In an
1
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
effort to ensure quality pipe is used in mining applications, ASTM International published two standard
specifications in 2012. The first (F2986) is for “Corrugated Polyethylene Pipe and Fittings for Mine
Leachate Applications.” The second one (F2987) is for “Corrugated Polyethylene Pipe and Fittings for
Mine Heap Leach Aeration Applications.”
In an effort to determine if these specifications were being followed and to survey the quality of pipe
used in mining, one dozen samples of corrugated pipe were obtained in the spring of 2015. Pipes were
collected from manufacturers in North America, South America, and the UK. These were all new pipes
headed to the field for installation. The purpose of this study was to compare the properties of these
production pipes to the requirements found in the new ASTM standards.
Some requirements for the two ASTM specifications are found in Table 1.
Table 1: PE Compound requirements of two ASTM standard specifications
Requirement
Property
Test method
Recycled allowed
ASTM F2986
ASTM F2987
No
No
density
ASTM D1505
>0.947 g/cm3
>0.947 g/cm3
Melt index
ASTM D1238
<0.4 g/10 min
<0.4 g/10 min
Flexural modulus
ASTM D790
>758 MPa
>758 MPa
(110,000 psi)
(110,000 psi)
>21 MPa
>21 MPa
(3000 psi)
(3000 psi)
Yield stress
ASTM D638
These properties are part of a Cell Classification system found in ASTM D3350. The properties have
historically been measured on the actual virgin pipe resins, but more specifications are written so the
properties are measured from samples from the pipe. These properties are similar to those found in
highway application specifications like AASHTO M294 (AASHTO-2014). The purpose of measuring
these properties is to ensure that a consistent type of polyethylene was used when manufacturing the
pipes. The basic controlling properties for polyethylene are the melt index and the density. The properties
in Table 1 relate to these.
The pipe properties shown in Table 2 are those specifically done on finished pipe for quality control
and quality assurance.
2
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
The dimensions, stiffness, and brittleness are specified to ensure a minimum set of properties exists
when the pipe is made. The first three properties in Table 2 give some indication of how a pipe may last
over many years of service.
The carbon content should be controlled because research by Bell Labs showed that 2.5% black was
the optimal amount to effectively block UV radiation for service lifetimes of greater than forty years
(Gilroy 1985). Therefore, most engineering applications that use black polyethylene require a carbon
black content of 2-3% in the compound.
Table 2: Additional pipe requirements of two ASTM specifications
Property
Test method
Carbon content
ASTM D4218
Requirement
ASTM F2986
ASTM F2987
2-3 %
2-3 %
>24 hrs
>24 hrs
>20 min
> 20 min
-0 to +4.5%
-0 to +4.5%
of nominal
of nominal
Varies with
Varies with
pipe size
pipe size
Varies with
Varies with
pipe size
pipe size
No cracks
No cracks
ASTM D1603
Stress crack
ASTM F2136
resistance (NCLS)
(50°C, 4.14 MPa,
Igepal CO-630)
Oxidative induction
ASTM D3895
time (OIT)
Inside diameter
Wall thickness
Pipe stiffness
Pipe brittleness
ASTM D2122
ASTM D2412
ASTM D2444
(3.9°C, 2.5 kg, 1.5m)
The NCLS stress crack resistance test is one of several ways to evaluate the material’s ability to withstand
an environment that promotes cracking. This particular test involves a small, dumbbell shaped specimen
into which a face notch of about 20% of the specimen’s thickness is cut. The specimens are then mounted
in a lever arm device and placed in an aqueous solution of 10% Igepal CO-630 at 50°C. Once the samples
reach the test temperature, a load equivalent to 4.14 MPa of stress is added to each. The time-to-failure
3
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
for each of five test specimens is recorded and the average time reported. The test is used to set a
minimum value for the application and as a way to show that appropriate HDPE resins are being used.
The oxidative induction time or OIT is a way to evaluate the additive packages found in the pipe.
The OIT test has been greatly misused over the years so it’s appropriate to state what it is and what it is
not:
 The OIT test does not, by itself, predict service lifetimes in oxidative environments.
 The OIT test cannot tell which stabilizers are present.
 A larger number in the OIT test does not necessarily mean better performance, unless the same
additive package is used in both samples.
 The OIT test indicates the presence of added stabilizers.
 Loss of OIT over time can be used to evaluate the effectiveness of different stabilizers.
There are a number of other properties one can measure to compare different pipe samples and to
generate more information concerning the long-term performance of the corrugated pipe. The first of
these is buckling strength.
The buckling strength can be determined simply by extending the test used to determine the pipe
stiffness. The stress on the pipe is increased at a constant rate until there is a peak in the load/deflection
curve. This can be useful because a variety of things can affect this value, such as wall thickness, resin
density, and the presence of fillers or other additives.
Another useful test for corrugated HDPE pipe is the elongation-at-break. The tensile yield stress
seems to be the only tensile property required in most pipe specifications. However, there is knowledge to
be obtained from the amount a tensile bar will stretch before it breaks. During a tensile test, every
specimen will fail at the location of the largest flaw. This can be a piece of dirt, a nick in the specimen, a
large carbon agglomerate, or anything else that acts as a break initiator. Very clean virgin compounds
exceed 800% elongation while even carbon black filled materials easily exceed 400% as long as the
carbon black is of high quality. Low elongation values in tensile tests can indicate the presence of fillers,
the use of poor quality carbon black, and even the presence of recycled HDPE in the sample. A proposed
specification for use of recycled resins in pipe suggested a minimum elongation of 150%. (Thomas,
2011).
Since low tensile failure values can indicate the presence of recycled polyethylene and/or fillers, two
other tests are useful to glean more information about the pipe.
The first one is the ash test. Ash is considered anything that is not organic. It could be a filler such as
calcium carbonate, a processing aid such as calcium stearate, or even bits of metal or glass often found in
samples of post-consumer recycled polyethylene. This test is most convenient to do along with the carbon
4
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
black test. After the polyethylene has been pyrolysedin the tube furnace or oven, all that remains is the
sum of the carbon black and the ash. This result can be over 10% if there are fillers. Therefore, if one then
burns off the carbon black, the percent ash will be obtained.
The second test determines if post-consumer recycled HDPE is present in the pipe. This test
determines the percentage polypropylene (PP) in the sample. PP is almost always found in post-consumer
recycled resins because it is largely composed of detergent bottles. Detergent bottles can contain up to
about 30% PP from the bottle closures and the spouts, both made from PP. Typical lots of post-consumer
HDPE can contain10-15% PP. The test involves a melting profile with a Differential Scanning
Calorimeter (DSC) (Thomas – 2011).
Methodology
Samples obtained
Twelve samples were obtained in the spring of 2015. Information about the samples is shown in Table 3.
Table 3: Pipe samples
Pipe number
Diameter mm
(in)
Manufacturer
Country
Perforations
1
375 (15)
1
Chile
No
2
250 (10)
1
Chile
No
3
375 (15)
2
Chile
No
4
250 (10)
2
Chile
No
5
300 (12)
3
USA
No
6
250 (10)
4
USA
Yes
7
200 (8)
5
Chile
Yes
8
125 (5)
5
Chile
Yes
9
150 (6)
6
UK
Yes
10
100 (4)
6
UK
No
11
100 (4)
4
USA
Yes
12
100 (4)
7
Mexico
Yes
5
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
This group of samples represents seven manufactures and seven different sizes. Six were perforated,
while the others were not. The distribution intends to provide a fair representation of drainage pipe used
in mining applications.
Tests performed
Each of these samples was subjected to a series of more than fifteen tests. The properties evaluated
included density (ASTM D1505), melt index (ASTM D1238), tensile yield stress (ASTM D638), tensile
elongation-at-break (ASTM D638), flexural modulus (ASTM D790/D3350), carbon content (ASTM
D4218), ash content (ASTM D5603), polypropylene content (NCHRP 696), stress crack resistance
(NCLS – ASTM F2136), oxidative induction time (OIT – ASTM D3895), high pressure oxidative
induction time (HPOIT – ASTM D5885), dimensions (ID, wall –ASTM D2122/F2986), stiffness and
buckling (ASTM D2412), and impact resistance (ASTM D2244).
Results and discussion
Since there are a large number of results to be presented and discussed, they are split into three sections.
These sections: Physical Properties, Mechanical Properties, and Durability Properties.
Physical properties
The physical properties of the pipe compounds are shown in Table 4.
Table 4: Physical properties of the twelve pipe samples
Sample-
Density
Melt index
% Carbon
% Ash
% PP
1-375
0.962
0.25
2.68
0.1
0.1
2-250
0.961
0.35
1.61
0.1
0.2
3-375
0.962
0.28
0.71
1.1
2.3
4-250
0.961
0.41
0.60
0.9
3.0
5-300
0.954
0.20
1.37
2.9
2.0
6-250P
0.961
0.11
1.72
0.7
0.1
7-200P
0.950
0.31
2.41
0.1
0.5
8-125P
0.958
0.38
1.87
0.3
0.3
9-150P
0.960
0.37
4.01
13.0
6.2
pipe type
6
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
10-100
1.070
0.38
4.31
9.3
5.3
11-100P
0.958
0.11
2.14
0.2
0.5
12-100P
0.963
0.45
2.04
0.2
0.7
These properties were all measured on a compression molded plaque made from the pipe. The plaques
were molded according to ASTM D4703. The density and melt index are the two main control properties
during the manufacturing of polyethylene resins. These are fundamental properties. The density is an
indication of the crystallinity of the PE while the melt index is related to the molecular weight of the PE.
Since these are independent properties, both are required to characterize PE resins.
Unfortunately, when the density is done by gradient density (ASTM D1505) or specific gravity
(D792), the results are influenced by other ingredients in the compound. For example, the density of
carbon black is 2.27 g/cm3 and the density of calcium carbonate is 2.72 g/cm3. Therefore, anytime fillers
or even are carbon black added, the density becomes more unreliable. ASTM D3350 allows for a
correction for added carbon black, but experience has shown the result is not always accurate. The value
of 1.070 g/cm3 for sample number 10 cannot be explained at this time.
The melt index measures how much melted sample flows through a standard sized orifice at a
standard temperature (190°C), and under a standard load (2.2 kg) during a period of 10 minutes. A large
majority of resins used in corrugated plaque manufacturing have a melt index of less than 0.40 g/10 min.
The ASTM standards for mining call for the percentage of carbon black fall between 2.0 and 3.0%.
Other corrugated pipe standards have had 2.0 – 4.0% and older standards had 2.0 – 5.0%. With the
requirement of 2.0 - 3.0%, only four of the twelve samples would meet the ASTM standard. This is not an
overly significant issue, but it is true that as one adds more carbon black, the pipe becomes more brittle.
Increased brittleness can lead to cracks during service and even reduce the buckling strength of the pipe
by reducing its flexibility.
The presence of ash is more alarming than the high carbon black values. First of all, when the ash
test is performed on virgin polyethylene, the amount of ash is almost immeasurable, and will be below
0.1%. We only report the value to 0.1% because the results are not as reliable as the value gets very small.
Ash content above a couple of tenths of a percent is often a sign of the pipe having recycled PE content.
Recycled materials are not necessarily bad. Research for the National Academies through the
Transportation Research Board (TRB) and within the National Cooperative Highway Research Program
(NCHRP) demonstrated that pipe containing 100% recycled PE can be made to exceed the requirements
for highway applications and have estimated service lifetimes of more than 100 years (Thomas - 2011).
However, recycled resins should only be used in low-risk applications or by those that truly understand
the limits involved with using recycled PE. In a situation where there are very high sustained loads, harsh
7
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
chemicals, and high temperatures, one would want to minimize the risk by using only virgin materials.
The two samples with nearly 10% ash should be a concern because large amounts of fillers negatively
impact the mechanical properties of HDPE. Once more, the long-term cracking resistance can be heavily
affected by added inorganic fillers.
When one looks at the percent black, the percent ash, and the percent polypropylene, a clearer
picture concerning recycled PE emerges. First of all, polypropylene can come from two different sources.
The first is the carrier resin in the carbon black concentrate. Color concentrates are most often sold as
50:50 blends of carbon black and PE. The PE used in color concentrates is most often post-consumer
recycled (PCR) resin, unless virgin resin is specified. If one starts with a 50% blend and wants to make
2.5% black in the final compound, the concentrate must be diluted 20:1. So, assuming there is 10-15%
polypropylene in the PCR carrier resin, the final PP content will be between 0.5 and 0.75%. Notice that
PP was detected in all twelve samples. Three samples had just a trace (<0.2%), four samples had between
0.3% and 0.7%, and the remaining five had from 2.0 to 6.2%. The last group shows that PCR-HDPE was
added to the final pipe formulation.
Mechanical properties
The next set of test results demonstrates the differences between the pipe samples when they are subjected
to mechanical stress. The results of different mechanical tests are shown in Table 5.
Table 5: Mechanical properties of the twelve pipe samples
Sample-
Yield
Break
Flexural
5%
pipe
stress (MPa)
strain (%)
modulus
Stiffness1
(MPa)
(kg/cm/cm)
type
1-375
24.58
139
967
2.952
2-250
27.32
120
1027
3.806
3-375
24.98
350
1008
3.057
4-250
26.85
131
899
4.073
5-300
25.96
81
1012
3.884
6-250P
25.19
251
1053
3.885
8
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
7-200P
23.42
91
925
4.017
8-125P
26.62
48
983
3.252
9-150P
23.88
12
1118
3.915
10-100
22.79
8
1109
3.979
11-100P
25.70
239
1000
6.595
12-100P
27.63
80
1167
3.460
1: Force per displacement per unit length
2: Force per unit length
The minimum required tensile yield stress is 20.60 MPa (3000 psi) in both ASTM pipe standards. All of
these pipes are well above the requirements. However, both standards also require a minimum base resin
density of 0.948 g/cm3. Based upon the relationship between yield stress and density found in the Plastic
Pipe Institute’s TR-43 (PPI – 2003), one can see that in order to meet the density requirement, the tensile
yield stress needs to be above 24.13 MPa (3,500 psi). Because the density measurements of those
compounds containing fillers and recycled materials are unreliable, the yield stress-density relationship
can be used to evaluate the densities of the base resins. The pipes with yield stresses below 24.13 MPa
include samples 7, 9 and 10. There is nothing out of the ordinary with sample 7 but samples 9 and 10
have high concentrations of carbon, fillers, and polypropylene.
The strain (elongation) at break values are related to the “flaws” in the pipe. Six of the twelve pipe
samples had break strains of less than 100%, and only three had break strains greater than 150 %.
Samples 9 and 10 are particularly worrisome because they broke at a strain near or at the yield point. This
should not be acceptable for any pipe product, especially for one used in designed structures like mine
heap leach pads. The presence of flaws can also affect the stress crack resistance of the pipes. A
sufficiently large flaw (critical defect) can initiate a stress crack.
All the flexural modulus results indicate that each of the pipe samples met the minimum required
value of 759 MPa. And, just like tensile strength, there is a relationship between density and flexural
modulus (PPI 2003). Therefore, with the density requirement of 0.948 g/cm3, all the flexural modulus
values should be greater than 863 MPa, which they are. These first three properties were measure on test
specimens taken from compression molded plaques. The next three properties were measured directly on
samples of pipe.
The 5% stiffness results represents the load required to reduce the inside diameter of the pipe 5%.
The units of kg/cm/cm are unusual. The value reported is the force (kg) required to compress the pipe,
9
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
normalized to the distance traveled (cm) and the length of the pipe sample (cm). Three of the pipe
samples failed to meet the minimum requirement for stiffness.
Durability properties
In an application such as this, there are a number of factors that will affect the long-term properties of the
HDPE pipe. These include the time-dependent response to stress and strain, the resistance to oxidizing
chemicals such as sulfuric acid, and the accelerating effects of elevated temperatures. Unfortunately, there
are only a couple of tests that address these important design considerations. Three tests were performed
that can be related to the materials long-term performance. They are shown in Table 6.
All three of these tests were performed on compression molded plaques made from the pipe. The
first test is a measure of the stress crack resistance of samples. The test is called the Notched Constant
Ligament Stress (NCLS) test and is a measurement of the time it takes for a face notch (cut about 20%
through the thickness of the specimen) to grow when the specimen is subjected to 4.137 MPa (600 psi) of
stress in a surfactant solution at 50°C. The required minimum value for this test in the two ASTM pipe
specifications is 24 hrs. Seven of the twelve samples did not meet this requirement. In fact, the average
values ranged from 6 to 548 hrs. This shows a very large difference in the pipes ability to resist cracking.
Table 6: Durability properties
Stress crack
OIT
HPOIT
pipe type
Sample
resistance (hrs)
(min)
(min)
1-375
11
40
246
2-250
10
18
244
3-375
16
13
88
4-250
7
6
62
5-300
71
74
326
6-250P
40
21
173
7-200P
548
60
335
8-125P
38
9
95
9-150P
13
14
78
10-100
14
6
66
11-100P
48
28
273
10
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
12-100P
6
13
139
The next test is the Oxidative Induction Time (OIT) test. This measures how long it will take a sample to
be consumed by oxygen at a test temperature of 200°C. The onset of oxidation is delayed by added
process stabilizers and long-term antioxidants. The minimum required value is 20 minutes in the
specifications. These samples showed a large range of values which went from a low of 6 minutes to a
high of 74 minutes. It seems reasonable to assume anti-oxidants would be consumed more rapidly in low
pH environments but this was shown to not be true for HDPE geomembranes (Abdelaal-2012).
The test can also be performed at a lower temperature (150°C) under an applied oxygen pressure of
3.448 MPa (500 psi). This High Pressure OIT (HPOIT) test is sensitive to a class of additives known as
Hindered Amine Light Stabilizers (HALS) (Thomas – 1993). These additives dramatically improve the
resistance of HDPE to UV exposure as well as acting as long-term antioxidants. A pipe containing HALS
and having a high number in this test should be more resistance to the effects of exposure to sulfuric acid.
This test is not required by the ASTM specifications, but one can see that the results ranged from 62 to
335 minutes.
Summary and conclusions
The purpose of the study was to measure various properties on a selected number of pipes made around
the world for mining applications. The focus has mostly been on heap leach pads because this is where
the environment is the most severe. The overburdens can be very high, the temperatures can be
significantly above ambient, and the pipes can be exposed to concentrated sulfuric acid.
The results obtained on a dozen different samples has demonstrated that the pipe sold into this
market is variable in terms of its composition and its mechanical properties. Some of the properties that
are believed to affect the pipes performance over its service lifetime are discussed below.
Recycled polyethylene
Five of the twelve pipes (42%) contained significant amounts of recycled PE based on the percentage
polypropylene in the samples. The presence of PP is specific for post-consumer recycled HDPE. Results
of an NCHRP study (Thomas – 2011) demonstrated that contamination is a main concern with the use of
PCR-HDPE and this must be controlled to ensure consistent performance in corrugated drainage pipe.
Contaminants influence the strain-at-break and the stress crack resistance, and probably play a role in the
buckling strength and long-term resistance to stress. Contamination can be controlled by specifying a
minimum strain-at-break and a maximum ash and polypropylene content.
11
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
Stress crack resistance
In other buried pipe applications, the resistance to cracking under a sustained load or strain has been
identified as a service life-limiting property. Therefore, minimum stress crack resistance requirements are
placed on corrugated HDPE pipe, even if it contains recycled and is used for land drainage, where the
overburden can be just 0.3 m. Our results show that the pipes used for mining varied from 6 to 550 hours
of average failure time in the NCLS stress crack test. To put this in perspective, the worst HDPE for stress
crack resistance, 100% post-consumer recycled HDPE and HDPE homopolymer have stress crack failure
times around 6-8 hrs. HDPE homopolymer is used to make milk jugs and is not good enough for
detergent bottles because it cracks when it is used for detergent bottles. Additionally, PCR-HDPE is
primarily made from detergent bottles and milk jugs. A reasonable NCLS average failure time is 24
hours, which was the value established for corrugated pipe under highways about fifteen years ago. Seven
of the twelve pipes tested (58%) failed to meet an average failure time of 24 hrs.
Oxidation resistance
Pipes used in copper mining may be exposed to hot concentrated solutions of sulfuric acid. Since this acid
initiates oxidation, the service lifetime could be partly controlled by the long-term antioxidants present in
the pipe compound. Tests that have been used to evaluate additive packages are the OIT test and the
HPOIT test. The two test methods for pipe used in mine applications have a modest OIT test requirement
of 20 minutes. This is less than the typical value of 100 minutes for HDPE geomembranes, but the pipe
has higher natural density (0.948 vs. 0.938 g/cm3), which gives it higher natural resistance to oxidation.
There really is not enough knowledge about how this pipe reacts to concentrated sulfuric acid to establish
a minimum value. However, seven of the twelve pipes (58%) failed to meet a modest requirement of 20
minutes.
Conclusions
The corrugated HDPE piping being used in mining operations today varies greatly in composition and
properties. The differences surely contribute to variable performance in the field. It would be beneficial to
the mining industry to understand how these products perform in service and how their long-term
survivability can be improved to increase the output and profitability of the mine. However, until product
specifications with defined minimum properties are adopted, the industry will continue to deal with
variability in product performance. ASTM International has published two specifications that if followed,
could bring more continuity to the corrugated pipes used in mining applications.
12
HEAP LEACH SOLUTIONS, 2015 ● RENO, NEVADA, USA
References
Abdelaal, F.B., Rowe, R.K., Smith, M., Brachman, R.W. and Thiel, R. 2012. Antioxidant depletion from HDPE and LLDPE
geomembranes without HALS in an extremely low pH solution, Proceedings of GeoAmericas 2012, Lima, Peru.
AASHTO. 2014. Standard Specification for Corrugated Polyethylene Pipe, 300- to 1500-mm (12- to 60-in) Diameter, American
Association of State Highway and Transportation Officials, Washington, D.C.
ASTM International F2986-12 Standard Specification for Corrugated Polyethylene Pipe and Fittings for Mine Leachate
Applications, ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania, 2012.
ASTM International F2987-12 Standard Specification for Corrugated Polyethylene Pipe and Fittings for Mine Heap Leach
Aeration Applications, ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania, 2012.
Goddard, James B. Profile wall polyethylene pipe specification development, Beijing International Plastic Pipe Exchange
Conference, Beijing, China, November, 2011.
Gilroy, H.M. 1985. Polyolefin longevity for telephone service, SPE/ANTEC 31.
PPI. 2003. Design service life of corrugated high density polyethylene (HDPE) pipe, Plastic Pipe Institute Technical Report TR43, Washington D.C.
Smith, M.E. 2004. Drainage pipe deflection for high heaps, The Mining Record, 4th Quarter.
Thomas, R.W. and Ancelet, C.R. 1993. The effect of temperature, pressure, and oven aging on the high pressure oxidative
induction time of different types of stabilizers, Proceedings of the Geosynthetics ’93 Conference, Vancouver, British
Columbia.
Thomas, R.W. and Cuttino, D.M. 2011. Performance of corrugated pipe made with recycled polyethylene content, NCHRP
Report 696, Transportation Research Board, Washington, DC.
13
View publication stats