Butt fusion

ISO/TR 11647 1996 Fusion compatibility of polyethylene (PE) pipes and fittings ISO 12176-1 1998 Plastics pipes and fittings - Equipment for fusion jointing polyethylene systems - Part 1 Butt fusion... 

Techniques, used by the gas and water industries to join and repair pipelines, include butt fusion, electrofusion socket welding and socket jointing (309). The study of bond strength testing for solvent joints in piping systems has noted extreme sensitivity to minor variations in sample preparation (259). 

PTFE (and other fluoropol5miers) tubes and lined pipes are welded by the butt fusion technique (Fig. 

Figure 7.16 (a) Welding device for (b) butt fusion welding of pipes. 

Munn. I. J.. and Georgiou. G. A. (1995). Ultrasonic and radiographic NDT of butt fusion welds in polyethylene pipe. Plastic Pipes IX Conf.. Scotland. UK, 18 21 Sept. 1995. 

A gas distribution system can be assembled using compression fittings, similar to those used on domestic water pipes, for pipes of diameter <63 mm. However, fusion joints which caimot leak, are more common. Socket fusion, used to join pipes of sizes up to 125 mm, involves the use of an injection-moulded socket that fits on the pipe ends. A simple socket allows straight continuation of the pipe, whereas 45 and 90° elbows allow sharp corners, and equal tees allow branches to be added. Butt fusion, used to make axial joints on pipes of diameter 63 mm and above, is preferred for diameters >180 mm. 

The procedure for the butt fusion of pipes has five stages... 

The most important application of hot-plate welding is in the joining of thermoplastic water, gas and effluent pipes, where it is often referred to as butt-fusion welding. It is also used by the automotive industry in the manufacmre of fluid reservoirs and in the welding of PVC door and window frames. 

Butt fusion n. A method of joining pipe, sheet or other forms of a thermoplastic resin wherein the ends of the two pieces to be joined are heated into the lower end of the polymer s melting range, then rapidly pressed together and allowed to cool, forming a homogeneous bond. ASTM D 2657 describes a recommended practice for butt-joining polyolefin pipe by heat fusion. 

Seams are fabricated by hot gas welding, extrusion welding, or by butt fusion. It requires considerable skill to hand fabricate using a rod and hot gas, so the vendor s welders should be checked as to their qualifications. Seams should be minimized. This can be done by using the widest sheet available (3 ft or wider) and by thermoforming heads instead of preformed sections. 

When butt fusion joints are to be used inside the shell, the preparation for these inside welds should be inspected. 

Pimputkar, S. M. The Dependence of Butt Fusion Bond Strength on Joining Conditions for Polyethylene Pipe. SPE ANTEC, pp. 455-57, May 1989. 

ASTM D 2609, ASTM D 2657, ASTM D 2683, and ASTM 3261 cover all types of joining for pipes and fittings—socket fusion, butt fusion, and saddle fusion. 

PTFE (and other fluoropolymers) tubes and lined pipes are welded by the butt fusion technique (Fig. 14.45). A uniform bead is required for the formation of a strong butt weld. The two ends of the plastic tubing are cut back to obtain square ends. The pipe ends are faced together by a device such as the one shown in Fig. 14.46 which allows the application of a measured axial force to the tubes. A heated plate or a clam shell heater can be used to heat the ends of the tube. An important step is to thoroughly clean and wipe the ends of the tube with acetone or another solvent. 

---