IMPROVEMENT OF RESIDUAL STRESS BY BUILD-UP WELDING ON OUTSIDE CIRCUMFERENTIAL SURFACE OF PIPE

摘要

PURPOSE:To improve the residual stress on the inside surface side of the butt joint weld zone of metallic pipes and to prevent generation of a stress corrosion crack by subjecting the outside surface side in said weld zone to build-up welding under a specified condition. CONSTITUTION:Residual tensile stress exists on the inside surface side in the weld zone and the heat-affected zone thereof and leads to a stress corrosion crack in the stage of forming a joint part by butt welding of metallic pipes to each other. A build-up weld zone 3 is formed on the outside circumferential surface in the butt weld zone 2 of metallic pipes 1, 1 in order to prevent such crack. The build-up welding is performed in this stage in such a way that the build-up ratio h/t with the height in the build-up weld zone 3 defined as (h) and the wall thickness of the pipe 1 as (t) is larger than 0.2 and that the value of the build-up width ratio L/Rt in the build-up part with the width in the part 3 defined as L and the radius of the pipe 1 as R is larger than 1. The residual tensile stress on the inside surface side of the weld zone 2 and the heat-affected zone 4 thereof is considerably reduced or made into compressive stress and the generation of a stress corrosion crack is obviated.