Joining 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). 

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 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. 

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. 

In most cases, fused-joint liners are joined outside of the existing sewer. Thermal-butt-fusion or the thermal extrusion welding method is used to join the liner. If SDR solid wall PE pipe is being used as a liner, it may be joined with the use of a stainless steel full encirclement clamp and the proper gasket material. This method is used when the work pit is not at a manhole. Sections of PE pipe with gasket joints can be assembled in the work pit with flow passing through the previously inserted sections. 

In socket fusion the eleaned ends of adjacent lengths of pipe are inserted into a socket that is heated to create the bond. The temperature of the socket is commonly raised by the resistive heating of wires embedded within it. The applied heat melts the interior of the socket and the exterior of the pipe ends to form the weld. Socket fusion involves less melt flow than butt fusion, so it is important that the surfaces to be joined be free of contaminants such as dirt, grease, and oxidation. As such joints are frequently made outdoors, rain and blowing dust can be troublesome. This problem can be alleviated to a great extent by the use of temporary welding shelters. 

ASTM DOT compliance testing was conducted at Continental Industries test facility in Broken Arrow, OK. Seven hundred forty seven (747) performance tests are complete or in progress to evaluate the use of PA 12 material for natural gas mechanical fittings. Most of the tests are eonducted with Performance 8100 PE gas pipe. PA 11 butt fusion joints have also been tested in our evaluation of PA 12 because that is the method Continental uses to join Con-Stab ID Seal stab fittings to the outlet of PA 11 mechanical tapping tees. Fusions were made with the same temperatures and melt times as used on PA 11 fittings. We did not experience any PA 12 fusion joints failures in the eourse of this evaluation. 

Optical fibers must often be joined, either permanently or temporarily, with minimal coupling loss and back-reflectiom Depending on the performance required, one of three methods are commonly employed to join optical fibers (1) fusion splicing, (2) mechanical splicing, or (3) butt-couphng mechanically aligned fibers terminated with cormectors. The flber ends to be joined must be clean, accurately aligned, and cleaved or polished, so the fiber end-faces are flat and parallel to each other. 

Heat fusion offers 3 types of joints. They are butt joints, saddle joints, and socket fusion. There are two spinoff joints for producing socket- and saddle-heat-fusion joints. The concept of a heat-fusion joint is simple. You heat two surfaces to a specific temperature and them fuse them together with an application of sufficient force. Done correctly, the two materials mix together and form a joint. This type of joint can be as strong as the pipe being joined. When a fused joint cools to near ambient temperature the joint can be handled and worked with. 

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