it is the object of the present invention a thermoplastic element for the protection against corrosion in the thermofused splicing of a thermoplastic tube to a thermoplastic connection , which element has the shape of a fully thermoplastic tubular sleeve , able to be introduced into a socket mouth formed by the expansion of the tube end , said splice element bearing only one internal diameter and two external diameters which define a cylindrical external portion of larger diameter and a tubular projection which diameter is smaller than the former , and which is introduced into the thermoplastic tube , a lateral wall of the external portion defining a front butt of said thermoplastic element against the end of the thermoplastic tube . said splicing element also exhibits an auxiliary ring which operates as a reference point for the assembly thereof .