P. Tayefi, S.B.M Beck and R.A. Tomlinson
Papers # 2014 Chicago
Electrofusion welding is a common jointing method for polyethylene (PE) pipe in the UK water industry. Here, electricity is used to heat a coil that melts the fitting and the host pipe of the same material. When the joint cools it forms a bond. However, premature failure of these can occur if best practice installation principles are not followed on site. Current literature fails to link failures associated with fatigue if the jointing system is installed incorrectly. Therefore, an experiment was designed with the aim to observe the severity that poor installation has on joint integrity.
A novel experimental rig, designed to be retrofitted to an existing servo-hydraulic fatigue testing machine, has been used to cyclically pressurise PE tapping tee fittings that have been created with a controlled element of contamination. Extensive fatigue tests have shown the relationship between joint failure and the dynamic pressures experienced in water distribution systems. Furthermore, the effects of contamination have shown to have a detrimental effect on electrofusion assets.
Additionally, a bespoke ultrasonic rig was designed and built to monitor the crack propagation of selected fittings during live dynamic tests to confirm the mode of failure. The system aimed to capture crack growth during a live test. The link between dynamic pressures, poor workmanship and failure modes are presented.