Abstract: A large-diameter plastic pipe is made by extruding from an extruding-nozzle assembly a hollow thermoplastic strip having an outer rectangular cross section and formed with longitudinally extending outer walls and webs having inner surfaces and defining a plurality of longitudinally extending internal cells separated by the webs from one another. Substantially only the inner surfaces of the outer walls and the cell-forming webs are then cooled to size the strip and provide it with a predetermined compressive strength stable up to a predetermined critical pressure of the design strength while externally shielding external surfaces of the strip and thereby preventing cooling of same.

Abstract: A large-caliber pipe consisting of thermoplastic, constructed from an extruded hollow plastic profile having helical turns welded along a helical contact seam. The hollow plastic profile is a multi-cell profile having a rectangular overall cross section and a rectangular cross section of the cells. The plastic has an integrated reinforcement consisting of embedded fibers in a quantity of 5 to 30% by weight, preferably about 10% by weight, based on the total weight. At least a proportion of the fibers is oriented in the direction of the turns. The orientation of the fibers results in an anisotropic modulus of elasticity and hence an increased annular rigidity and stability.