A New Method for Measuring the Bond Strength of Electrofusion Joint

Abstract

Electrofusion (EF) technique is very widely used in connecting polyethylene and its composite pipes. Safety of pipeline system depends on the quality of joints. For EF joints, the quality is characterized by the bond strength of welding interface. Peel test is a normal method for measuring the bond strength for EF joints. In our previous study (PVP2012-78655), we used the peel test to analyze the bond strength for EF joints with cold welding defects by calculating the bonding energy of fusion interface. However, in most well electrofused joints, test specimens fail in the pipe, rather than the fusion interface. As a result, it is difficult to determine the optimum welding conditions with the method of peel test. In this paper, a new method for measuring the bond strength of EF joint is proposed. A set of horizontal apparatus is designed and specific improved test means are introduced. Test results are then presented, which proves the effectiveness of the new method for high strength joints and in reducing pipe deformations. Finally, criteria to estimate the bond strength of joints are investigated. A comparison is made between the criterion of mean percentage decohesion presented in ISO 13954 and the criterion of normalized decohesion energy, which reveals that the latter one is more practical in statistics for peel tests, with better normality, a good concentration of data and facility to rank EF joints of different types.