PLASTIC PIPE, METHOD OF ITS MANUFACTURE AND METHOD OF CONNECTION OF PLASTIC PIPES Russian patent published in 2001 - IPC

FIELD: manufacture of plastic pipes. SUBSTANCE: sizes of pipe and protective layer are so selected that relationship of outer diameter of pipe to thickness of protective layer is no less than 70 or at least 100 which is preferable; cohesive strength of outer protective layer exceeds that between outer protective layer and inner pipe at least at ends of pipe but for any lines of minimum resistance. Method of manufacture of plastic pipe includes joint (biprofile) extrusion of molten plastic materials from extruder from which inner pipe and outer protective layer are molded, bringing the molten plastic materials in contact in hot state and cooling them under natural conditions so that outer protective layer should be separated from inner at least at the ends of pipe. Uncovered area of inner pipe is now fit for welding by means of electric current. EFFECT: most advantageous combination of mechanical strength and protection against environment. 36 cl, 4 dwg