A review of the electrofusion joining process for polyethylene pipe systems

Abstract

Electrofusion joining is now an essential and widely used method to assist in the creation of polyethylene pressure pipe systems. The process of electrofusion joining is reviewed by examining the experimental and some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying fusion time and pipe/fitting gap influences the strength of electrofusion joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint has no strength. Second, a joint formation and consolidation stage where an increasing joint temperature aids molecular diffusion to both increase 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 plateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within reasonable limits). Finally there is a cooling stage where the joint bridging “tie molecules” become locked into either side of the joint. It is these tie molecules that give the joint its ductility and strength. The concluding section of the review notes some of the important on‐site practices that, if followed, allow electrofusion joints to acquire their good strength properties, and hence give polyethylene pressure pipe systems of a high integrity.

Experimental and numerical investigation of barreling at the cut ends of solid and skinned PE pipes

“…8, cold zones are located at both sides of the fusion zone to block off the extrusion of any molten polymer from the fusion zone [5]. Therefore, excessive gaps between the coupler and the pipe may result in insufficient build up of melt pressure and lower interface temperatures as the melt flows outside the cold zones, reducing the joint strength [5,6]. The dimensions of the cold and fusion zones for each pipe according to the UK WIS-4-32-14 standard [29] are also shown in Fig.…”

“…Whereas in butt welding the pressure is usually applied through axial compression in EF joining it builds up as the internal surface of the coupler, and the external surface of the pipe in contact with it, melt and expand. Regions near each end of the coupler, and half-way along it where the pipe ends meet, remain unheated: these cold zones maintain the pressure by restricting axial extrusion of molten polymer from the fusion zones [5]. Therefore, excessive gaps between the coupler and the pipe may result in insufficient build up of the melt pressure and lower interface temperatures as the melt flows outside the cold zones [5,6] reducing the joint strength.…”

Electrofusion Joining Technology for Polyethylene Pipes Using Carbon Fiber

“…고분자의 열융착에 대한 열공급원으로는 Heated tool, Gas, Light beam, Ultrasonic, Friction, High frequency heating 등이 있다 (Runčev and Trokovski, 2008). 고분자 소재인 Polyethlene 배관을 사용함에 있어서 (Moon and Takaku, 2005;Andrews and Ward, 1970;Bowden and Young, 1974 (Bowman, 1997;Caravaca et al, 2007 (Fig. 4).…”

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

“…There are several established techniques for joining of PE pipeline such as fusion welding, friction welding and mechanical joints, but by far the most popular method is electrofusion (EF) welding [9][10][11][12]. EF welding usually entails fitting two PE pipes inside a PE fitting or coupler and then melting them together by passing a high current through a high resistance wire element contained within the fitting, see Fig 1 [8].…”

“…The high current causes the wire to heat up, which in turn melts the surface of the PE pipes and fitting causing them to fuse together. The fusion process usually takes 24 to 90 seconds to provide acceptable joint strength [13] which should be as strong as the substrate material being joined [11]. The process can be distinguished by four key steps: i) the incubation period (when the electrical current is introduced and the joint has no strength), ii) the joint formation and consolidation (after fusion, the gap is filled and the PE is molten), iii) the plateau region (the strength stabilizes with respect to fusion time), and iv) the cooling period (crystallization).…”