Excellent impact performance of PVC pipeline materials in gas distribution networks after many years of service

It has been about fifty years ago since the first unplasticized poly(vinyl chloride) (uPVC) pipes were installed for use in gas distribution purposes. Currently, about 22,500 km of uPVC is still in use in the Dutch gas distribution network. The pipes were originally designed for a lifetime of 50 years, but due to positive experiences the question arises if (and how long) the lifetime can be extended without any concessions to safety. This is supported by the data of leak surveys presented in this paper. The amount of leaks per installed km of uPVC is even slightly lower than that of polyethylene or steel pipes. Only impact modified PVC has a better performance. The impact behaviour is presumed to be the limiting factor for the lifetime of uPVC. Therefore, the impact behaviour was studied as a function of the age. Two types of research have been carried out: instrumented falling weight tests were carried out on recently produced uPVC pipes (some of which were aged artificially) and tensile impact tests were carried out on excavated uPVC pipes which had been in service for 20 to 50 years. The overall conclusion that can be drawn from these experiments is that the most significant change in impact behaviour is likely to occur in the early stages, just after the production of the uPVC pipe. Physical ageing occurs on a logarithmic timescale, thus the changes occurring between the 20th and the 50th year of service are relatively small compared to the changes that occur in the first 20 years. This leads to the conclusion that uPVC pipes that currently show good impact behaviour, are expected to have good impact properties for many years to come.