Fusion weld method and assembly for forming a fusion welded joint between pipe sections

In combination, a pair of pipe sections having the same exterior diameter and ends abutting generally along a transverse abutment plane;

• and a fusion weld assembly for forming a fusion welded joint between the pipe sections, the fusion weld assembly comprising:
• an elongated annular collar made of thermoplastic material and having an interior diameter closely approximating the exterior diameter of the pipe sections to closely coaxially receive the pipe sections in close-fitting, end abutting relation along a transverse abutment plane, the collar including a pair of internal annular recesses longitudinally spaced apart on opposite sides of the abutment plane to define an internal thermal barrier land, each of the recesses having the same interior diameter;
• and
• a welding sleeve including a pair of annular sleeve sections disposed in the pair of recesses, respectively, each sleeve section having a plurality of turns of electrical resistance wire sheathed in thermoplastic material and further having an outside diameter approximating the diameter of the recesses, the thermoplastic material of the welding sleeve, the collar and the pipe sections being fusible at their interfaces at a predetermined melting temperature upon passage of electrical current through the wire whereby the collar and the pipe sections are bonded together, the presence of the thermal barrier land preventing fusing of the abutting ends of the pipe sections, the interior diameter of the sleeve sections approximating the outside diameter of the pipe sections whereby thermal expansion of the pipe sections adjacent the sleeve sections during passage of electrical current through the wire closes any clearance space between the sleeve sections and the pipe sections.

A method for forming a fusion welded joint between a pair of pipe sections having the same exterior diameter and made of thermoplastic material, the method comprising the steps of:

• extruding an elongated cylindrical collar out of thermoplastic material;
• heat treating the collar to relieve internal stresses;
• machining the collar to provide an interior diameter approximating the exterior diameter of the pipe sections for coaxially receiving the pipe sections in close fitting relationship;
• providing a pair of internal annular recesses in the collar in a longitudinally spaced apart relation to define an internal thermal barrier land between the recesses;
• forming a welding sleeve including a pair of annular sleeve sections which each have a plurality of turns of electrical resistance wire sheathed in thermoplastic material terminating in a free end and which are electrically connected together, and which each further has an outside diameter approximating the diameter of the recesses and an interior diameter approximating the interior diameter of the collar;
• fitting the annular sleeve sections in the pair of recesses, respectively;
• inserting the pipe sections in the collar with the ends of the pipe sections abutting generally along a transverse abutment plane passing approximately through the middle of the thermal barrier land;
• and
• applying electrical current to the free ends of the wire until the thermoplastic material of the collar and pipe sections expands at their interfaces to close any clearance therebetween, and continuing until the material at the interfaces melts and thermally expands to develop pressure in the recesses and bonds the collar and pipe sections together, the presence of the thermal barrier land preventing fusing of the abutting ends of the pipe sections.