In-Service Durability of uPVC Water Mains

In order to determine whether uPVC pressure pipe performance is affected by time in service, sections of uPVC water mains of ages up to 16 years have been exhumed and tested. From a combination of quality and mechanical property tests it is shown that initial pipe quality is the overriding influence in determining pipe performance.

uPVC pipes, which were first used as water mains over 25 years ago, currently have about 50% of the market share for pipe renewals and new works. This usage of uPVC is not spread evenly across britain, some engineers remain reluctant to specify it owing to its poor historical performance (11, whilst others are concerned that the pipes may age and become more susceptible to brittle failure with time in service. The work described in this paper was undertaken in collaboration with Severn Trent Water Authority, to determine whether the durability of uPVC water mains is affected by time in service.

uPVC is a viscoelastic material and therefore its properties are expected to change with time. Various research workers have investigated this phenomenon but they have used new pipes and artificially aged them by heat. In particular L C E Struik (2) found that the effect of artificial ageing on uPVC, using a variety of temperatures and times, is to make it stiffer and more brittle and to reduce the rate of stress relaxation of the material, whilst Schwencke (3) concluded that the effect of artificial ageing, which can be achieved by storing pipes at 60°C for 17 hours, is to increase their creep resistance and strength. A variety of preliminary tests carried out at WRc did not show artificially aged pipes to behave in the same way as pipes which had been in service for many years. It was decided that a study of properties of genuinely old pipes would provide results which could be interpreted more easily.

In this study pipes which had been in service for up to 16 years have been exhumed and tested in the ways described as follows.

In order to reduce the number of variables a single pipe size and class, 4 inch diameter class C (operating pressure 9 bar), from a single manufacturer was chosen for study. Pipes of a range of service ages which had experienced similar service conditions were exhumed. The manufacturer with the most extensive records of quality control and type testing for past production was chosen to allow this data to be compared with similar test data generated from tests on the exhumed pipes.