RESIDUAL STRESS RELIEVING METHOD OF PIPE CIRCUMFERENTIAL WELD ZONE

摘要

PURPOSE:To relieve residual stress of weld zone by expanding the pipe circumferential weld zone from the inside by the use of a pipe expander after finishing of the final pass welding. CONSTITUTION:A pipe expander is not used until welding is completely finished. Upon ending of the final pass welding, tensil stress above the yield stress of the pipe is given to the weld zone to generate a slight plastic deformation. Next, the tensile stress having been applied is removed, whereby the residual stress is relieved. Any type of the pipe expander may be used as far as it is used for ordinary pipeline laying, etc. The size and expanding capacity of the pipe expander need be changed depending upon the materials, sizes, thiknesses, etc. of the pipes but if it restrains the shrinkage of the pipe in its radial direction during welding and is able to assure that the shrinkage in the circumferential direction after removing load of the pipe expander is above yield strain 80%, it is applicable. The mechanical stress to be applied to the weld zone gives the same effect even when it is applied from the outside of the pipe.