Polyethylene pipe with outer protective sleeve for laying above ground level comprises prefabricated core pipe with outer protective, post-extruded polyolefin sleeve of minimum specified thickness

摘要

An inner polyethylene core pipe is enclosed by a protective tubular sleeve, >=1mm thick, of a pure or modified polyolefin, preferably polypropylene. The sleeve is post extruded onto the core pipe. An additional protective sleeve, >=0.5mm thick, may be applied onto the inside of the core pipe by coextrusion. Material used for the protective sleeve has a slightly different thermal conductivity to that of the core pipe and melts more slowly than the core pipe material so that no mixing of materials occurs. An independent claim is included for a butt welding process for joining the sleeve protected pipe in which the ends of the pipes and outer sleeve are heated and pressed together. A conventional polyethylene welding bead formed fills the gap between the ends of the protective sleeve and grips parts of the sleeve ends. When solidified the bead and excess sleeve material are removed to give a smooth outer surface.