| 摘要 |
It is an object to provide a residual stress improving method for a pipe by imparting larger compressive residual stress on the pipe to sufficiently reduce tensile residual stress in order to prevent the stress corrosion cracking. With respect to a stress improving region where the residual stress of a pipe is to be improved, a load in the axial direction of the pipe is made such stress making axial strain of the outer surface of the pipe 0% or above and being yield stress of the pipe or below, and internal pressure of the pipe is raised. The pipe is plastically deformed and is expanded in the radial direction by the internal pressure. After the internal pressure is raised to the degree the pipe is plastically deformed, the internal pressure and the axial load are removed, and thereby compressive residual stress is imparted to a welding section and a heat affected zone which are the stress improving region of the inner surface of the pipe.
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