Assessing the risk of failure and remaining useable life of polyethylene water mains

Polyethylene potable water mains with an assumed minimum design life of 50 years have been in widespread use in the UK water industry for more than 30 years. In the 1980s and 1990s Severn Trent Water buried two polyethylene pipe test beds in the Midlands that was fully analysed chemically and mechanically before installation. A recent UKWIR funded collaborative project has exhumed several of these pipes and repeated these tests. Analysis on these pipes showed that some of the newest PE100 pipes could last as long as 160 years. It also confirmed the relationship between certain chemical markers such as antioxidant concentration and carbonyl levels and the mechanical performance of the pipe.

Based on these test results and the statistical analysis performed, combined with previous work performed on artificially aged samples, a risk assessment methodology for the UK’s polyethylene pipe water network was derived. Further to this, a procedure to perform a statistically robust risk assessment on the networks of the water companies was produced. This procedure sets out the number of samples required, methods for obtaining the sample test methods for the chemical analysis, and methods for calculating the remaining useable life of polyethylene pipe from the results.

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