Process for manufacturing the inner tube element for a double tube coring apparatus

Claim 1

Process for manufacturing an inner tube element (1) for a double tube coring apparatus, said element consisting of a rigid tube length (2) having a substantially constant section, made of synthetic resin and provided with couplings (3, 4) for connecting it to other inner tube elements, in which process at least one metallic nipple (3) is placed onto a cylindrical winding mandrel (11) at a predetermined axial position corresponding to the length of tube element to be manufactured, a part of said nipple (3) having an inner diameter substantially identical to the diameter of the mandrel (11) and having a rough surface (14), and fibers (16) coated with a synthetic resin are wound helically onto said cylindrical mandrel (11) so as to overlap the rough surface (14) of said nipple (3) the process being characterized by the further steps of providing said nipple (3) both with a gripping ring (13), and helically winding the fibers (16) onto the mandrel (11) and onto the gripping ring (13) in order to allow the tube element to withstand axial tensile stress in a double tube coring apparatus, and also with an annular shoulder (25) with which the threaded portion of a connected inner tube element comes in abutment when the nipple is screwed home and on which the resin body of said connected inner tube element may rely in order to resist axial compression stresses.