Abstract: The invention relates to a process for manufacturing an inner tube element made of synthetic resin for a double tube coring apparatus provided for deep boring. The tube element is provided with coupling nipples for connecting it to other inner tube elements. Fibers coated with synthetic resin are wound helically onto a cylindrical mandrel so as to overlap each nipple. This process gives the tube element a higher strength than that of glued nipples.

Abstract: An inner tube element for a coring apparatus comprising a double tube, made of synthetic resin reinforced with fibers and provided at its ends with connecting nipples, is entirely made of synthetic resin and overlaps, at each of its ends, a part of the nipples having a rough surface gripped by said fibers, preferably in the form of webs of glass fibers.The inner tube element is manufactured by a process in which two nipples or couplings are placed onto a cylindrical mandrel having a constant section and rotating about its longitudinal axis, at a predetermined distance corresponding to the tube element to be manufactured, a part of said nipples having an inner diameter substantially identical to the diameter of the mandrel and having a rough surface, and fibers coated with a synthetic resin are wound helically onto said cylindrical mandrel, so as to overlap the rough part of said nipples.

Abstract: An inner tube 2 of a core barrel is releasably locked within an outer tube 1 by pivotable latch feet 32 engaging an annular recess 31 in the outer tube. A retrieving head 3 is slidably coupled via a pin 40 and slot 41 to the inner tube, and carries sealing rings 6 disposed, during coring, within a recess 5 in the outer tube to permit fluid passage. To retrieve a core sample in an ascending boring the pressure in the lower part of the column is reduced, whereupon the retrieving head drops by gravity to seal off the outer tube. A pin 37 on the inner tube then drops to cam release the latch feet and unlock the inner tube from the outer tube. Thereafter, as the lower column is drained, the inner tube and retained core sample descend by gravity down through the outer tube to a retrieval site.