17 NON-METAL JUNCTIONS FOR PIPES, NON-METAL TUBING AND TUBING COUPLINGS FOR JOINING AND TERMINATING PIPES, PLASTIC PIPES FOR CONVEYING NATURAL GAS, INSULATING MATERIALS, NAMELY, INSULATION AND GASKETS FOR UNDERGROUND PIPES, INSULATION JACKETS FOR INDUSTRIAL PIPES; FLEXIBLE PIPES NOT OF METAL; INSULATION TO BE USED IN INDUSTRIAL PIPES AND PIPE-SYSTEMS