REDUCING METHOD OF RESIDUAL STRESS AT CIRCUMFERENTIAL WELD ZONE OF STEEL PIPE

摘要

PURPOSE:To reduce the residual stress at the circumferential weld zone of steel pipes as far as possible by making use of the advantages of a local stress relief annealing method which is used for residual stress relieving of the circumferential weld zone after butt welding and preventing the production of new residual stress after stress relief annealing being a disadvantage. CONSTITUTION:The butt circumferential weld zone of steel pipes and its neighborhood are so heated as to become maximum temperatures 580-700 deg.C after finishing of welding so that the maximum heating temperature area thereof is held in a range of more than 5 times the wall thickness of the pipes to the right and left with the weld line as a center. Or heat treatment is so accomplished that the distances between the positions reaching 450 deg.C on the outer side of said maximum heating temperature area and the weld line are held at more than 10 times the wall thickness of the pipe respectively to the right and left of the weld one and even temperature distributions are given in the thickness direction of the pipes. In this way, the residual stress of the weld zone of the butt-welded steel pipe may be reduced.