Abstract: The process for the production of a thermoelectrically weldable zone in thermoplastic materials is significantly improved by the true-to-size, air-free embedding of the heating conductor at a clearly defined depth below the joining surface. For this purpose in a first process step a sublevel wire bed bottom is cut in the material, in which is cut a substantially inverted T-shaped incision, running in two planes and at the desired depth, measured from the material surface and, following the surface profile, the cut is passed along the heating conductor insertion line. Using the same tool the cover strips formed are raised and stretched along the path of cut, so that an open channel is formed with the sublevel wire bed bottom. Preferably in the same operation the wire bed is also cut true-to-size with a cutting tool and corresponding to the heating conductor. In a later process step the heating conductor is placed through the still open channel, the cover strips are pressed and then melted.

Abstract: Pipes to be joined and a pipe coupling have an outer sleeve made of a material optimized for linear and radial strength and positive connection and an inner portion or liner optimized for chemical inertness and the tightness of the connection. The pipes and coupling part are shaped to accommodate a material-correct joining procedure. Compound pipes (1) have a rigid, relatively thin pipe outer sleeve (3) for absorbing and transferring forces and a softer, relatively thin liner or inner pipe (4) to form a tight connection and inert sealing with respect to the rigid outer wall. Like the pipe, the coupling part (2) is made of a rigid joining outer sleeve (5) and a weldable socket (10), preferably made of the same material as the liner (1). Welding energy is introduced electrically.