Abstract: A coupler 10 consists of a length of cross-linked polyethylene pipe having a spiral groove 16 cut in its outer surface and another spiral groove cut in its inner surface. A heating element 18 is wound in the groove. The coupler is expanded mechanically so as to have an easy fit over the ends of polyethylene pipes 12, 14. The heater element 18 is energized and the coupler shrinks and forms fusion welded joints between itself and the pipes. No preparation of the pipe ends is necessary because the serrated inner surface cuts through the oxidized skin and bonds to material beneath the skin. The coupler is especially advantageous in large sizes of 500 mm or above. Instead of an electric heater, radiant energy, e.g. infra red or light is used to heat the coupler. For example, an array of reflector lamps can be used circumferentially located around the coupler.