If a product or system has a long life – whether below or above the ground – it invariably improves its value within the circular economy. Predicted lifetimes of below ground plastic pipe systems are now well over 100 years – according to research undertaken by TEPPFA, the European plastic pipes and fittings group. This research has seemingly shown that for polyethylene (PE) pressure pipes for example, reliable working lifetimes have been found to be in excess of 200 years.
All products have modes of failure and in the case of PE plastic pipes, excluding non-time dependent ductile rupture failures due to excessive pressure, the main types of failure are stress cracks and oxidation. However, continuing work in developing newer variations of these materials is helping to reduce the occurrence of both of these factors. The TEPPFA research also showed that PE gas pipes last even longer than PE water pipes, as chlorine in water initiates an oxidation degradation mechanism. Despite this slow oxidation, the research has shown that these late life failure modes (wear) are likely to start at about 235 years from original installation2 – over two centuries is a significantly long timespan.
Other research from TEPPFA shows that plastic pipelines require fewer repairs during their lifetime3 and are subject to fewer defects or leakage developing, such as through fissures, displaced joints, deformation or infiltration.
As always, good installation is key to maximising the lifespan of below ground plastic pipes. If best practice techniques are followed, including the correct types of pipe and fittings, clean and effective joints and correct trench depths and materials, the pipe can be installed and remain undisturbed below ground for many decades – even centuries.
Pipe network requirements and loads do vary during their lifetimes so for example if additional service pipes are required, these can be fitted to PE pressure pipes via branch saddles drilled into the live pipe, minimising invasion to the existing system.