Plastic tubular connecting sleeve for a pipe with internal liner

A tubular junction sleeve of thermoplastic material suitable for being inserted inside a pipe comprising at least two steel pipe elements that are internally lined with a thermoplastic material where the ends of the two welded together pipe elements are assembled end to end, said sleeve presenting at each end a tubular wall terminal portion of thickness that is smaller than the thickness of the adjacent running portion of the tubular wall of said sleeve, said sleeve presenting a Joule effect heater wire at at least one of said terminal portions of the sleeve, and preferably at each of them, the wire being arranged in a spiral at the outer surface of said terminal portion of said sleeve, wherein said heater wire is folded in half so as to form a double spiral made up of two wire portions arranged side by side forming two substantially equidistant spirals that are joined together at a common end constituted by a hairpin-bend, each spiral traveling along said outer surface of each terminal portion of the sleeve from the first end of the spiral closest to the inner surface of the tubular wall of the sleeve towards a second end of the spiral constituted by said common hairpin-bend end, said second end of the spiral being closer to the outer surface of the running portion of the sleeve adjacent to said terminal portion of the sleeve, the two non-spiral-wound free ends of the two portions of the wire at said first ends of the two spirals preferably being at the inner surface of the sleeve, said two free ends of the two portions of the wire at said first ends of the double spiral including two electrical power supply terminals of said wire and thus being capable of being united side by side with a common electrical connector at the inner surface of the sleeve.