LOW PRESSURE SEWERS AND THEIR HDPE PIPE – AN ENVIRONMENTAL
NIGHTMARE?
The Low Pressure section of the Cudjoe Regional Wastewater System (CRWS) will have over
100 miles of High Density Polyethylene (HDPE) Pipe, ranging in size from 2” to 8” that will be
buried 2’ to 4’ under the surface. It will be under pressures of 15psi to 60psi. The Low Pressure
System is asserted to be a low cost, reliable, wastewater collection system that will save money
on initial sewer system installation. But what are its long term costs? . Could it be an
environmental disaster in the future due to pipe failures? Or perhaps a financial disaster if the
piping needs replacement in a few years?
The Florida Keys are a series of coral (limestone) islands. In most areas of the lower Keys, there
is salt water flowing only a few feet below the surface. Limestone, with a high water table, is
naturally unstable. Sink holes, dips, settling of buildings and shifting roadbeds occur over time.
Idiots dig and drill without checking. Each home with a grinder pump (projected to be 2,800)
will pump into a series of headers and ultimately into an 8” plastic line that runs over 20 miles
from Big Pine to Lower Sugarloaf. In addition, 275 lift stations that consist of large concrete
tanks with up to 5 grinder pumps will take the gravity feeds and pump them into the same
lines.
The problem, in general, is that HDPE pipe has a tendency to become brittle and crack over
time. It is inevitable that failures will occur at some time in the future. Our specific problem is
that when cracks occur and effluent leaks, it is very likely that it will go right into our porous
limestone aquifer. Eventually the effluent will reach our pristine waters, but this could be some
distance away. Complicating things is that there is no way to monitor for leaks in a pressure
system. With gravity, when there is a leak, salt water will leak into the pipe and be detected at
the waste treatment plant and looked for in the manholes it flows through. A vacuum system
line failure is noticed immediately and can be found through simple diagnostic troubleshooting.
A leak in a pressurized sewer system might go undetected for months or longer. We may
discover that the incremental improvement in sewage treatment we seek is lost through a
collection system that is ill designed for our environment.
There is an excellent web site at http://hdpefailures.com/ that provides numerous examples
of failures and should have been read by our County Engineer before this system was signed
approved. For other ways the LPS/grinder system costs more, go to
www.newtoncoalition.com or contact us at info@newtoncoalition.com.
Walt Drabinski
Sir Isaac Newton Coalition
The specifications for our system followed by samples of info on HDPE failure. We need to
remember the names of the people prominently displayed on the next page.
SECTION 15018
HDPE FORCE MAIN PIPING
PART 1 - GENERAL
1.01 DESCRIPTION
A.
This specification governs the material, pipe, fittings, joining methods and general
construction practice for High Density Polyethylene (HDPE) piping systems.
1.02 QUALITY ASSURANCE
A.
References, American National Standards Institute (ANSI), American Society for
Testing and Materials (ASTM), Federal Specifications (FS), International
Standards Organization (ISO), and manufacturer’s printed recommendations.
A.
Pipe shall be manufactured from a PE 3408 resin listed with the Plastic Pipe
Institute (PPI) as TR-4. The resin material shall meet the specifications of ASTM
D3350-02 with a minimum cell classification of PE345464C. Pipe shall have a
manufacturing standard of ASTM D3035. The pipe shall contain no recycled
compounds except that generated in the manufacturer's own plant from resin of
the same specification from the same raw material. The pipe shall be
homogeneous throughout and free of visible cracks, holes, foreign inclusions,
voids, or other injurious defects. The pipe shall be identified for the application by
a green colored stripe AND, for long term identification, “Low Pressure Sewer
FM” shall be debossed (indent imprinted) in the identification line of the pipe.
1. Pipe & Fittings for 1-¼" Service Laterals shall be SDR 9 IPS HDPE
2. Pipe & Fittings for 2" & 3" Force Main shall be SDR 13.5 111 IPS HDPE
3. Pipe & Fittings for 4" and Larger Force Main shall be SDR 13.5 111 DIPS
HDPE
Sample Articles from http://hdpefailures.com/
HIGH DENSITY POLYETHYLENE PIPE WATER AND SEWER FAILURES
High Density Polyethylene (HDPE) Pipe is used in water and sewer pipe installations across the
United States. The pipe system is typically joined by thermal fusion or "welding" through the
use of "butt-welding" equipment or "electro-fusion" saddles that are often used in trench to
connect HDPE pipe segments. The American Water Works Association publishes standards for
HDPE pipe used in water mains and transmission lines (AWWA C906) and in service lines
(AWWA C901). However, the common HDPE pipe failure modes are not addressed in HDPE
pipe manufacturer literature or the reference pipe standards. Listed below are some examples of
HDPE pipe failure modes that are frequently encountered in the field. These issues should be
considered and addressed proactively in the pipe material selection process, the subsequent
design and construction process.
City of Dalton, Georgia:
Once held out as an HDPE success story and case study, Dalton, GA is a city
with thousands of feet of HDPE pipe that was installed in the late 1990's and
early 2000's.1 Dalton's experience with HDPE pipe has been challenging. By
the end of 2005, Dalton reported about 450 failures.
Example of HDPE pipe splitting experienced by Dalton, Georgia (2011).
HDPE Pipe Failures by Year and Type for 2003, 2004
and 2005
HDPE Failure Type
2003
2004
2005
Fusion
73
93
113
Pipe Split
14
93
66
With expenses totaling $916,741.17 – that included emergency repair costs
of $234,390.93 for 2003 and 2004 alone, Dalton Utilities proactively set out
to determine why their HDPE pipes were failing. Both the pipe manufacturer
and an independent testing lab reported that the pipe was fully compliant
with the governing pipe standard (AWWA C906). Dalton purchased electronic
pressure gauges to monitor their operating pressures at all locations where
HDPE pipe splits were occurring and retained several independent
laboratories and experts to determine the cause of HDPE pipes' poor
performance. Their independent consultants concluded, "the results
(pressure gauges) did not reveal any high, cyclic pressure events in the
pipeline that could be related to the root cause of the pipe failures". The
consultant further stated that, "it appears that the pipeline is operating at
pressures within the range claimed by the pipe manufacturer and as
specified".
HERNANDO COUNTY, FLORIDA:
Hernando County, FL is currently in design for a replacement of
approximately 10,000 LF of an HDPE water main that has seen numerous
failures over the past 6-7 years (Hernando Beach WM Replacement). The
6"and 8" DR17 DIPS HDPE line has experienced approximately 30 splitting
failures since the line was commissioned.
Failed 6” HDPE pipe from the Hernando County water distribution system (2010)
Some Plastics Can Be Adversely Affected by Drinking Water
Disinfectants
Research has Established that Common Drinking Water Disinfectants
Degrade Polyethylene (HDPE & MDPE) Pipe: Research dating back to
the 1950's documents oxidation of polyethylene polymers1,2,3 It is
understood that the amount and type of oxidants, that are added to disinfect
drinking water, attack polyethylene pipes and can cause premature aging –
and failure. Reports of HDPE water pipe failures have linked the failures to
oxidative degradation. The two largest water utilities in the world, Veolia
Environnement and Suez Environnement experienced a rash of HDPE service
line failures – which were initially thought to be ductile in nature (warmer
soils can soften plastic pipe causing bursts). Upon closer examination – the
failures were brittle in nature – indicating chemically induced embrittlement.
Veolia and Suez spent millions of dollars and eventually built a pressure
testing laboratory that could simultaneously test approximately 400 samples
under various pressures, temperatures and disinfectant regimes. They also
exhumed over 200 samples of in-service HDPE pipe from around the world
(including North America). Analysis of the laboratory testing and subsequent
correlation with the forensic examination of field samples has been published
in respected peer review journals.4,5,6,7 Veolia's and Suez's findings are
consistent with others in the world of polymer research. It is now readily
accepted that HDPE pipes are subject to degradation and therefore pose a
threat for possible premature failure in water disinfectant environments –
particularly in warmer environments. 8,9,10,11,12,26
Failed HDPE Water Line, France–
Suez Environnement 2009
6” Failed HDPE Water Line, USA –
Duvall, Edwards 2010
Edwards, et al. Failure Analysis of Polypropylene Used in Hot Water
Environments – Effect of Different Stabilizer Systems, ANTEC 2007.
Choi, et al. Modeling Stress Corrosion Cracking in Plastic Pipes, ASCE
Pipelines 2008.
Rozental-Evesque, et al. A Reliable Bench Testing for Benchmarking
Oxidation Resistance of Polyethylene in Disinfected Water Environments,
Plastic Pipes XIV, 2008.
Further Forensic Analysis of Field Exhumed Pipe in the United States
(US) Has Confirmed HDPE Pipe Oxidation: In 2007, Jana Laboratories
(Toronto) published a paper for the ANTEC plastics conference that
examined a number of exhumed HDPE pipe samples and reported, “..it
would appear that the failures are generally consistent with the Mode 3
Oxidative Initiation-Mechanical Propagation type of failure”.15 In 2009,
Engineering Systems Inc., led by Dr. Donald Duvall (a noted polymer expert
and former technical manager of one of the largest HDPE pipe
manufacturers) conducted a study that examined over 50 HDPE pipe
samples from 13 US water utilities which found varying degrees of oxidation
induced degradation in the samples (23 were from failure sites).13, 14 Failures
which are suspected to be related to oxidation have occurred and continue
to occur across the US. Las Vegas Valley Water District is in the process of
replacing 86,000 HDPE service lines due to pre-mature aging and failure.16
HDPE service line failures in cities such as Mesquite, NV; Pomona, CA;
Henderson, NV; Bakersfield, CA; Maui, HI; Hamilton, OH; Laughlin, NV; HB
& TS, TN have all been linked to oxidative aging in potable water service.13,14
Scott, Charles, Forecasting Pipe Replacements Using Weibull Analysis,
Society for Maintenance and Reliability, Annual Meeting, 2007.
Service Temperature and Type of Disinfectant Influence the
Degradation Phenomenon: The problem of oxidative degradation in HDPE
pipes has been particularly severe in areas with higher water temperatures
that use either chlorine dioxide disinfectant or chlorine (hypo-chlorite)
disinfectant.6 Accordingly, some HDPE pipe manufacturers have modified
their warranties to limit coverage in oxidative environments.17 The Australian
trade association, PIPA (Plastics Industry Pipe Association of Australia),
printed an advisory in 2010 that stated, “Especially at service temperatures
above 20°C, chlorine dioxide will shorten the service life of polyethylene
pipes. For this reason chlorine dioxide water disinfection should not be used
with polyethylene, polypropylene or polybutylene (i.e. polyolefin) pipes.” 18
Duvall, et al. Oxidative Degradation of High Density Polyethylene Pipes
from Exposure to Drinking Water Disinfectants, 2009.
Appropriate Design Guidance is Lacking, but Needed: There is a real
need for practical, quantitative guidelines for prospective HDPE pipe users
and their design engineers. Outside of some very general warnings, the only
guidance currently being provided by the manufacturers of HDPE pipes is in
the form of very general chemical compatibility charts that do not consider
pressurized environments or long term exposure and express only vague
warnings on unspecified “pressure reduction” or “service life
reduction”.20,21,22 A recent JANA Laboratories paper, sponsored by the
polyethylene pipe trade association – Plastics Pipe Institute, looked at some
chlorine and chloramine (did not include chlorine dioxide) disinfected waters
and reported that,
“… a methodology has been developed for characterization of the Mode 3
(oxidation) long-term aging mechanism. This methodology for forecasting
long-term aging for this mechanism shows that performance is a function of
the water quality, water temperature, and operating stress and varies by
utility.” 23
However, the quantitative details for applying the methodology are not
disclosed and are not available for use by designers. Certainly, one of the
greatest challenges in applying any methodology, once released, will be the
difficulty in being able to accurately anticipate all of the potential changes in
water quality, temperature and stress that could take place in the coming 50
to 100 years for any system.
Finally, Carollo Engineers reviewed the existing literature in 2007 and their
investigations also found that premature aging of HDPE in potable water
lines was a failure mode which was not well understood in the US, but
should be addressed by the relevant pipe standards.19 Carollo found that
HDPE oxidation in water disinfectant environments is a problem not currently
addressed by the HDPE pipe standards. ASTM and AWWA are silent on
guidance for engineers and owners who require guidance in the area of
prevention of premature aging of HDPE pipe.
In Summary –Polyolefin Materials such as Polyethylene (HDPE) are
Inherently Susceptible to Oxidation by Chlorine Based Water
Disinfectants. Pipe Industry Design Guidance to Account for Factors
that Impact the Rate of Oxidation Induced Aging such as
Temperature, Disinfectant Concentration, Pressures in Isolation or
more Importantly in Combination Do Not Exist:
Polyethylene is a polyolefin family polymer – just like polypropylene and
polybutylene. As a polymer family, polyolefins are more susceptible to
oxidation through a free radical mechanism than other plastics. Antioxidants are added in polyethylene pipe formulations to extend their service
lives (the anti-oxidants are preferentially attacked by the free-radicals and
“sacrificed” – as long as they are available in the pipe). However, premature
failures of HDPE water pipes have demonstrated that under some operating
conditions the antioxidants are depleted and serious degradation of the pipe
occurs. This is why PVC, not HDPE, pipes are typically used for swimming
pool piping and manifolds where chlorine contact with plastic is required.
Polyolefin pipes are not recommended for service in highly oxidative
environments, which includes some drinking water systems. The idea that
polyolefin pipe materials are subject to oxidation induced failure is not new
to the pipe industry. In fact, the $1.1 billion Polybutylene Pipe Settlement
Fund was the result of a legal class action that centered around the
susceptibility of polybutylene pipes to fail in home plumbing systems where
warm chlorinated water contributed to premature embrittlement and
cracking.25 Another class action settlement featured polypropylene water
heater “dip-tubes” where polypropylene dip tubes failed prematurely due to
oxidative attack and resulting embrittlement. 24 While the polyethylene pipe
industry has sponsored a study that positions “100 year life” as expected for
polyethylene pipelines in water disinfectant environments (chlorine,
chloramines – not chlorine dioxide), it remains the only study that comes to
that conclusion. 23 On the other hand, the vast majority of research studies
(both exhumed pipe forensics and controlled laboratory studies) point to
premature oxidation induced aging as an important failure mode in
polyethylene pipe systems. Despite this set of facts, pipeline designers still
have no meaningful guidance from third party sources that can reconcile the
various factors (pressure, temperature, disinfectant type, disinfectant
concentration) which have been shown to affect HDPE pipe degradation in
oxidative potable water environments.
End Notes:
1. C.K. Haywood, “Oxidation and Ageing,” Chapter 6 in Polythene, ed. A.
Renfrew & P. Morgan, Interscience Pub., New York (1957).
2. J.H. Heiss & V.L. Lanza, “The Thermal Embrittlement of Stressed
Polyethylene,” Wire, October, 1958, pgs. 1182 – 1187.
3. H. Kambe, “The Effect of Degradation on Mechanical Properties of Polymers,”
Chapter 9 in Aspects of Degradation and Stabilization of Polymers, ed.
H.H.G. Jellinek, Elsevier Scientific Publishing, New York (1978).
4. Colin, et al. Aging of Polyethylene Pipes Transporting Drinking Water
Disinfected by Chlorine Dioxide I. Chemical Aspects, Polymer Engineering
and Science, 2009.
5. Colin, et al. Aging of Polyethylene Pipes Transporting Drinking Water
Disinfected by Chlorine Dioxide Part II –Lifetime Prediction, Polymer
Engineering and Science, 2009.
6. Rozental-Evesque, et al. The Polyethylene Life Cycle, ASTEE 2009, Nice,
France.
7. Devilliers, C. et al Kinetics of chlorine-induced polyethylene degradation in
water pipes, Polymer Degradation and Stability, March 2011.
8. Hassinen, et al. Deterioration of Polyethylene Pipes Exposed to Chlorinated
Water, Polymer Degradation and Stability, 2004.
9. Dear, et al. Effect of Chlorine on Polyethylene Pipes in Water Distribution
Networks, Journal of Materials: Design and Applications, 2006.
10.
Choi, et al. Modeling Stress Corrosion Cracking in Plastic Pipes, ASCE
Pipelines 2008.
11.
Water Research Foundation, Dietrich, A. et al. Chemical
Permeation/Desorption in New and Chlorine-Aged Polyethylene Pipes, 2010.
12.
Eng, J. et al. Cytec Industries, The Effects of Chlorinated Water on
Polyethylene Pipes, Plastics Today, March 2011.
13.
Duvall, et al. Oxidative Degradation of High Density Polyethylene Pipes
from Exposure to Drinking Water Disinfectants, 2009.
14.
Duvall, D.E., Edwards, D.B. Forensic Analysis of Oxidation
Embrittlement in Failed HDPE Potable Water Pipes, American Society of Civil
Engineers, Pipelines proceedings 2010
15.
Chung, et al. An Examination of the Relative Impact of Common
Potable Water Disinfectants (Chlorine, Chloramines and Chlorine Dioxide)on
Plastic Piping System Components, ANTEC 2007.
16.
Scott, Charles, Forecasting Pipe Replacements Using Weibull Analysis,
Society for Maintenance and Reliability Professionals, 15th Annual
Conference, Louisville, KY, 2007.
17.
Charter Plastics, 50 Year Limited Warranty PE 3408, PE 3608 and PE
4710 Potable Water Pipe, 4/21/11
18.
Plastics Industry Pipe Association of Australia Limited (PIPA) “Chlorine
Dioxide Disinfectant for Drinking Water – Effect on Pipe and Seal Materials”
July 2010
19.
Carollo Engineers, Evaluating the Compatibility of Chemical
Disinfectants with Plastic Pipe Materials Used for Potable Water Distribution –
Technical Memorandum, August 2008.
20.
Performance Pipe (website), Who says HDPE isn’t tough Enough to
handle chlorine?
21.
Chevron Phillips Chemical Company LP , Performance Pipe Field
Handbook, June 2012.
22.
Plastics Pipe Institute, Technical Note 19, Chemical Resistance of
Thermoplastic Piping Materials, 2007.
23.
JANA Laboratories, Technical Report, Impact of Potable Water
Disinfectants on PE Pipe, June 2010.
24.
Edwards, et al. Failure Analysis of Polypropylene Used in a Hot Water
Environment –Effect of Different Stabilizer Systems, ANTEC 2007.
25.
Cox vs. Shell Oil Company (Polybutylene Pipe) 11/17/1995 Date of
Settlement
26.
Cytec Industries, "The Effects of Chorinated Water on Polyethylene
Pipes", Plastics Engineering, October 2011.