Patent ID: 9085811
Filing Date: 2015-07-21
Classification: C21D

Abstract:
1. A method for improving a residual stress in a pipe, comprising: improving the residual stress in an inner surface of the pipe to the compressive direction by cooling of the inner surface of the pipe after heating of the pipe; wherein the heating is to heat a vicinity of a welded part of the pipe from an outer surface of the pipe to raise the temperature to a construction temperature below 350° C., the cooling is to cool the inner surface in the vicinity of the welded part of the pipe by supplying cooling water into the pipe, the heating and the cooling are repeated twice or more, an outer surface temperature of the pipe is measured using a temperature measuring unit when the cooling water is supplied for the cooling of the inter-surface, and it is determined whether a maximum value of a lowering rate of the outer surface temperature of the pipe, obtained without inner surface temperature measurement, satisfies a lowering rate target value of the outer surface temperature, the lowering rate target value being a function of a thickness of the pipe in a measuring position of the outer surface temperature.