the coupling of two tubular elements is achieved by welding them together by energization of an electrical resistance element , the one element comprising a male end , the other a socket end . the coupling operation is carried out by means of a composite connecting piece comprising two rings which are fitted on one another , one acting as a support for a bifilar electrical resistance element and the other as a sheath . the electrical resistance element is thus uniformly coated in plastic material and is accurately centered , thereby ensuring uniform heating and welding . this coupling method is for use in coupling discharge pipelines for waste water and rain water and for conduits for industrial fluids .