Claims
- 1. A method of prestressing a tubular apparatus having at least one metal inner tube positioned within and spaced apart from a metal outer tube, the method comprises connecting the inner tube to the outer tube at at least two locations spaced along the length of the tubular apparatus with the walls of the inner and outer tubes spaced from each other, and then, which the tubes are connected, expanding increasing the diameter of at least a major portion of the inner tube between said locations so as to permanently shorten the inner tube whereby a tensile prestress is applied to the inner tube and a compressive prestress is applied to the outer tube with the inner and outer tubes remaining spaced from each other.
- 2. A method according to claim 1 wherein the step of increasing the diameter of at least a portion of the inner tube comprises drawing a mandrel at least partly through the inner tube.
- 3. A method according to claim 2 further comprises increasing the diameter of the inner tube to a diameter equal at least to the diameter of the mandrel at at least one of said two locations before connecting the inner tube to the outer tube at said at least one of said two locations.
- 4. A method according to claim 1 further comprises increasing the diameter of the inner tube at at least one of said two locations before connecting the inner tube to the outer tube at said at least one of said two locations.
Parent Case Info
This application is a continuation-in-part of co-pending application Ser. No. 413,284, filed Aug. 31, 1982, now U.S. Pat. No. 4,470,188.
US Referenced Citations (9)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
413284 |
Aug 1982 |
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