PVC-A pipes. ductile-brittle transition in failure mode. new tests to evaluate the resistance of the crack growth.

In 1989 the English and Welsh water industry was privatised. A research program was conducted to develop new testing and quality procedures. So many pipes, taken from mains placed in service over time, were disinterred and tested. The failure causes were analysed mainly by application of “fracture mechanics”. To try to examine the long-term transition in failure mode (ductile-brittle) we must know the conditions that control the initiation and growth of crack. The concepts of toughness and fracture mechanics were introduced. The tests were carried out on pre-notched samples cut in form of C-ring. Following an extensive research program it was established that adding an elastomeric modifier such as CPE to PVCU, the yield stress or strength was reduced a little compared to PVC-U, but the toughness is enhanced, so we always have a ductile material. This research allowed the development of PVC-A (A=alloy). It meets the requirements of BS PAS 27 of 3/99. It is approved by the UK Drinking Water Inspectorate.