Method for assembling thermoplastic tubes by induction welding

A method of assembling together two tubes of thermoplastic materials, wherein said assembly is performed by welding by heating two contact surfaces of revolution that are pressed one against the other and that belong respectively to two portions, of two tubes placed in abutment or overlapping coaxially (XX′), the two tubes comprising a) a first tube constituted by a rigid tubular junction sleeve made of thermoplastic material inserted coaxially inside a first steel pipe element that is metal-welded or that is to be metal-welded in abutment with a second steel pipe element, and b) a second tube constituted by a coating of thermoplastic material applied as a liner of said steel pipe elements,

• wherein said assembly is performed by welding by induction heating one or more of a plurality of conductive welding elements, and that is arranged at the interface between the two contact surfaces, of the two tubes made of thermoplastic materials, by generating a magnetic field at said one or more conductive welding elements so that a melting of the thermoplastic materials constituting said contact surfaces as a result of said induction heating of said one or more conductive welding elements provides a continuous and leakproof weld at said interface over at least one closed loop around the entire perimeter of said interface,
• wherein an electromagnetic field is generated at said interface using an electromagnetic induction coil arranged coaxially inside the two tubes and the one or more conductive welding elements arranged so as to provide a plurality of coaxial circular welding zones arranged side by side in parallel along the axial direction (XX′) of said tubes, and
• wherein the conductive welding elements comprise a plurality of conductive welding balls arranged circularly so as to extend around the entire circumference of said interface in cross-section, the plurality of conductive welding balls having been integrated into the tubular junction sleeve during fabrication of the tubular junction sleeve.