Plastic Pipe Facts™

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 6
Failed HDPE Water Line, France– Suez Environnement 2009 6” Failed HDPE Water Line, USA – Duvall, Edwards 2010

 

General Oxidation Localized Oxidation

Edwards, et al. Failure Analysis of Polypropylene Used in Hot Water Environments – Effect of Different Stabilizer Systems, ANTEC 2007.

 

Microcrack

Choi, et al. Modeling Stress Corrosion Cracking in Plastic Pipes, ASCE Pipelines 2008.

 

Ageing Bench

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

PESL Failures by Month

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

Thick degraded layer Multi-axial cracks

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.   Anti-oxidants 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.