JPS5485143A - Generating method for residual stress due to local heating - Google Patents

Abstract

PURPOSE:To generate tensile residual stress at outside of a pipe and compressive residual stress at inside of the pipe even in limited place, by heating the welding zone from outside so as to give continuously local temp. gradient to the pipe. CONSTITUTION:Heating instrument, e.g., tungsten electorde 2 etc. of a TIG welding machine is arranged at the outside surface 1a of a pipe 1 near the welding zone so as to heat rapidly a prescribed position P for a prescribed time. When the outside temp. of the pipe lowers, thermal stress is generated between the position P at outside surface 1a and the position Q at the inside surface 1b. In addn., when the pipe 1 returns to ordinary temp., tensile residual stress remains at the position P and compressive residual stress at the position Q. Heating of inside surface and cooling of outside surface generates compressive residual stress at the outside of a pipe, thus improvidng the characteristics regarding the stress corrosion cracking or corrosion fatigue. Selection of heat input allows to control stress residued.