A REVIEW OF THE ELECTROFUSION JOINING PROCESS FOR POLYETHYLENE PIPE SYSTEMS

Electrofusion joining is now an essential and widely used method to as sist in the creation of polyethylene pressure pipe systems. The proces s of electrofusion joining is reviewed by examining the experimental a nd some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying f usion time and pipe/fitting gap influences the strength of electrofusi on joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint h as no strength. Second, a joint formation and consolidation stage wher e an increasing joint temperature aids molecular diffusion to both inc rease the joint strength and promote a more ductile mode of failure. A plateau region then follows where the joint strength, and ductility, remain reasonably constant despite the fusion time increasing. This pl ateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within r easonable limits). Finally there is a cooling stage where the joint br idging ''tie molecules'' become locked into either side of the joint. It is these tie molecules that give the joint its ductility and streng th. The concluding section of the review notes some of the important o n-site practices that, if followed, allow electrofusion joints to acqu ire their good strength properties, and hence give polyethylene pressu re pipe systems of a high integrity.