IMPROVEMENT OF RESIDUAL STRESS OF PIPE

摘要

PURPOSE:To generate residual compressive stress to the inside surface of a pipe and to prevent generation of stress corrosion cracking by heating inductively the pipe which contacts with a corrosive material by plural high frequencies of different frequencies in the thickness direction to heat the inside and outside surfaces of the pipe at different temps. then cooling quickly the pipe. CONSTITUTION:An induction heating coil 2 is disposed on the outside circumference of a metallic pipe 1 and the current A having the modulating wave consisting of two kinds of high frequencies of different frequencies or the current B superposed with two high frequencies of different frequencies is passed therein to heat inductively the pipe 1 at different depths in the thickness direction thereof thereby heating the pipe at the temp. difference given to maintain the inside surface temp. of the pipe lower than the outside surface temp. The pipe is then cooled to generate residual tensile stress to the outside surface of the pipe and residual compressive stress to the inside surface of the pipe. Even if a corrosive material is brought into contact with the inside of the pipe, generation of stress corrosion cracking to the inside surface of the pipe is obviated owing to the residual compressive stress.