JPS55110729A - Improvement of residual stress in steel pipe - Google Patents

Abstract

PURPOSE:To prevent the development of stress-corrosion cracks by the procedure in which a great stress is brought about in any one desired side of steel pipe, subjected to tensile yielding, and then cooled to ordinary temperature so as to retain compressive stress in the portion so treated. CONSTITUTION:The steel pipe 1 is fitted with the gas, electric heat, or high-frequency induction heater 3 in such a way as to surround the welded junction 2. Then, the outside of the steel pipe 1 is heated and at the same time the inside of steel pipe is rapidly cooled by passing a cooling medium, e.g., water in the inside of the steel pipe, whereby a great tensile stress is caused in the inside surface layer of the steel pipe 1 and at the same time a compressive stress is caused between the inside and outside of the surface layer. Under such a condition, the steel pipe is cooled to ordinary temperature to retain the compressive stress in the inside surface of the steel pipe and also the tensile stress in the outside surface. Thus, the lowering of the fatigue strength of the outside surface can be suppressed to a minimum and also stress-corrosion cracking due to the compressive stress can be prevented.