Abstract: A process for producing multi-layer composite tubes involves extruding an inner plastic tube prior to forming a metallic tube around the inner plastic tube which is subsequently covered with an outer plastic layer. The metallic tube is initially formed to have an inner diameter which is substantially greater than the outer diameter of the inner plastic tube. Subsequent to welding to seal the metallic sheet into the form of a tube, the excess diameter of the metallic tube is reduced in a manner which avoids stretching or elongating the tube. Adhesive coatings can be applied between the various constituent layers of tubes, and a mesh can be interposed between the metallic tube and the outer plastic layer.