JPS56130432A - Improvement for residual stress of pipe - Google Patents

Abstract

PURPOSE:To improve a corrosion resistance and a fatigue endurance in a weld zone of a pipe by laying residual compressive stress on inner and outer surfaces of a weld zone through quenching an outer surface immediately after heating while cooling an inner surface thereof. CONSTITUTION:In pipe materials 1, 1' welded at a weld zone 2, a cooling water flows inside the pipe to cool, and at the same time a heating coil 3 of ring shape provided outside the weld zone 2 heats up the pipe locally by high frequency current from a high frequency heating device 5, rendering a residual compressive stress to an inner surface of the pipe and a residual tensile stress to an outer surface of it. Next, a cooling device 6 is arranged around an outer surface of the weld zone 2 and cooling medium 9 is made gushed out by opening a valve 8, quenching an outer surface of the pipe including the weld zone. In the outer surface of the pipe, a tensile yield is generated at the time of quenching, but a residual compressive stress is inversely generated with a complete cooling, thus the pipe in a state of residual compressive stress in both inner and outer surfaces is obtained, so that there is no decreases in a corrosion resistance and a fatigue endurance based on a residual tensile stress in the pipe.