Abstract: By expanding a plastic pipe while it is still hot and expandable and thereafter shrinking the so-expanded pipe to a defined point of shrinkage where the pipe is cooled, e.g., by a water spray, it is possible to produce pipes of any diameter within a range using only one extruder die orifice. The expansion and shrinking is carried out using a double cone external mandrel. The process of the invention has the advantage of allowing the production of plastic pipe of any diameter specified by a customer without having to change the die orifice of the extruder.