Mechanical stress improvement process

摘要

A process is claimed for removing the residual tensile welding stresses in the inner layer of the weld metal and the heat-affected zone of steel piping elements that have been butt-welded to each other end-to-end by means of a circumferential weld. The process involves mechanically introducing circumferential compressive stresses in the piping elements by applying a radial load inwardly on a section of at least one of the piping elements away from the weld such that the distance from the midplane of the section of the piping element upon which the radial load is applied to the weld midplane is equal to about two to about 12 times the thickness of the piping element upon which the radial load is applied. The distance from the edge of the section of the piping element upon which the radial load is applied that is adjacent the weld to the weld midplane is at least equal to about one-half the thickness of the piping element upon which the load is applied. The amount of the radial load applied is sufficient to permanently reduce the outside diameter at the midplane of the section of the piping element in the range of about 0.2 to about 2.0 percent.