Abstract: During the electrofusion welding process of polyethylene pipes, the strength of electrofusion joint is mainly determined by the time elapsed during the diffusion entanglement stage of the polyethylene molecular chains at the interface between the sleeve and pipe. There is an relationship between the time and depth of the fusion zone extended to the inside of the pipe. To explore the relationship between the depth of the fusion zone and welded joint performance, a depth measurement method for the fusion zone was proposed by means of ultrasonic technique, and a series of experiments were carried out for the depth measurement of the fusion zone in the pipe as well as the joint performance characterization. The experimental results indicated that the depth of fusion zone was related to the interfacial welding strength. When the depth was controlled within a certain range, the basic peeling strength and interface ductility could be obatained. On the basis of these results, a new method was proposed to determine the welding time of the electrofusion joint in terms of measuring the depth of fusion zone. Furthermore, the deviations caused by various factors such as temperature, welding voltage and wire resistance were fully considered to make this new method more suitable for practical engineering applications.

Key words: polyethylene pipe, electrofusion joint, welding performance, ultrasonic inspection, fusion zone