Study on the Failure Mode of Cracking Through the Fitting of Electrofusion Joint

Electrofusion (EF) technique has been widely used in polyethylene and its composite pipeline system. The strength of the EF joint is regarded as higher than that of present pipe, for the EF joints are usually failed at the pipe when subjected to internal pressure. However, several recent studies from different researchers have revealed that the EF joint may fail by cracking through the fitting in the long-term hydraulic pressure tests. In this study, the structure parameter and loading condition were taken into consideration to investigate the failure mechanism of this failure mode. The progress of crack initiation and propagation was studied by FEA method and linear elastic fracture mechanics theory. EF joints with different structure and welding parameters were analyzed to find out the design factors which would have major influence on the failure mode of cracking through the fitting. The analytical results show a reasonable agreement with experimental observations, and also reveal that the length of inner cold welding zone has a great influence and should be carefully determined in the designation of EF fittings.