JPS57149428A - Heat-treating method for double pipe structure - Google Patents

Abstract

PURPOSE:To prevent the cracking of a welded part, by imparing a compressive residual stress to a welded part between an inside pipe and an outside pipe shorten than the inside pipe to offset a tensile residual stress formed in the welded part. CONSTITUTION:The outside pipe 6 shorter than the inside pipe 5 is fitted around the inside pipe 5, and the both end parts of the pipe 6 are welded to the peripheral surface of the pipe 5. Subsequently, by heating the pipe 6 locally in an axial direction and circularly in a circumferential direction e.g. with an induction heating coil 11 or by putting a fluid 25 into a gap between the pipes 5 and 6 under pressure and then heating the pipe 6 in the same way as the above-mentioned heating method, the outside pipe 6 is deformed to a drum type. In this way, the welded part is loaded with a tensile yield and then the pipe 6 is restored to its original form to impart a compressive residual stress to the welded part. Thus, the tenisle residual stress in the welded part is offsetted by the compressive residual stress, so that the cracking of the welded part is prevented.