Abstract: Formation of continuous grooves on the internal surface of a tube shell, in a single continuous cold drawing step, in which the tube shell is first sunk in a die over a reduced diameter cylindrical mandrel portion so that the diameter of the inner surface of the tube shell is reduced to a dimension below the base of the grooves of a grooved plug portion of the mandrel thereby retarding longitudinal movement of a portion of the reduced internal surface of the sunk tube shell at a plurality of circumferentially spaced intervals to effect formation of longitudinally continuous shallow grooves. The mandrel is allowed to rotate if it is desirable to facilitate the formation of spiral grooves on the tube inner surface.

Abstract: A method of fabricating a tube having enlarged ends and made of material which can be strengthened by cold working comprises fabricating a pre-form having the overall configuration of the tube but with increased outside diameters and a decreased length. The pre-formed tube is cold forged or cold rolled over its entire length to reduce its outside diameter while maintaining its inside diameter substantially fixed. This elongates the tube and reduces its cross-sectional area. Cold working is continued until the final desired dimensions for the tube are reached. This produces a strengthening effect by cold working over the entire length of the tube.

Abstract: A method of fabricating a tube having enlarged ends and made of material which can be strengthened by cold working comprises fabricating a pre-form having the overall configuration of the tube but with increased outside diameters and a decreased length. The pre-formed tube is cold forged or cold rolled over its entire length to reduce its outside diameter while maintaining its inside diameter substantially fixed. This elongates the tube and reduces its cross-sectional area. Cold working is continued until the final desired dimensions for the tube are reached. This produces a strengthening effect by cold working over the entire length of the tube.

Abstract: A method of prestressing a tubular apparatus having coaxial inner and outer metal tubes which are connected to each other at axially spaced locations. After the inner and outer tubes are connected to each other so that the tubular apparatus may be heat-treated or otherwise processed before it is prestressed, the diameter of at least a portion of the inner tube is increased so that it is shortened to thereby establish a prestressed condition between the inner and outer tubes with the inner tube under tension and the outer tube under compression.

Abstract: A method of prestressing a tubular apparatus having coaxial inner and outer tubes which are connected to each other at axially spaced locations comprises, after the inner and outer walls are connected to each other and the tube is heat-treated or otherwise processed, reducing the diameter of the outer wall so that the outer wall is elongated. The elongation of the outer wall establishes a prestressed condition between the inner and outer walls, with the inner wall under tension and the outer wall under compression. The reduction in diameter of the outer wall can be accomplished by using a roll extrusion machine, a tube reducer or a draw bench.