Electrofusion coupler

A fusion welding socket for use in coupling together plastic pipes, wherein the socket (18) is intended to receive the ends of pipe parts (1, 2) to be coupled together with a tight fit, and has embedded therein heating coils (24-27) which comprise resistance wires or filaments and which, when energized, function to fusion weld the socket material to the material in the pipe walls at the positions of said coils, wherein the diameter of the ends (19) of the socket is greater than the diameter along an intermediate part (20) of said socket;

• the diameter at said socket ends is adapted to receive, with a close fit, an outer pipe (1) and the diameter along said intermediate part is adapted to receive, with a close fit, an inner pipe (2) of a double-pipe conduit which includes two coaxial pipes and a leakage detection space (3) located between said coaxial pipes;
• the socket includes heating coils (24-27) comprising resistance wires or filaments which enable the socket material to be fusion welded with the material of both the outer tubes (1) and the inner tubes (2) of two double-pipe conduits to be connected together with the aid of the socket, locally at the positions of said coils;
• and the socket includes at least one passageway (21) which mutually connects the spaces in the socket on both sides of the intermediate part (20).