Process of forming an irregular surface on the inside of a tube or pipe

Abstract

An apparatus and method are provided for forming tubing and pipe with the inside surface of the pipe wall shaped irregularly for the purpose of either reducing boundary layer drag of a fluid flowing through the pipe or for anchoring a protective lining within the pipe. The apparatus includes an extruder having a die and a mandrel extending through the die for defining the inside surface of the extrusion. In one form, the mandrel is longitudinally oscillated to form circular serrations in the wall of the extrusion formed over the mandrel. In another form, the mandrel is rotated to provide circular or spiral serrations in the wall of the pipe. In yet another form, an electromagnetic field is generated and is varied in intensity in the vicinity of the extrusion die so as to cause variations in the dimensions of either or both the die and the mandrel located therein for varying the surface configuration or roughness of both the internal and external surfaces of the tube or pipe extruded through the die.

Dependencies are inferred from the claim text.