Abstract: An object of the invention is to provide a simple method and apparatus for evaluating a collapse load of a structure with respect to ductile fracture in the case where a plurality of flaws exist in a cylindrical structure that receives a bending load. The invention is an evaluation method and apparatus in which a result obtained by calculating a collapse load while a flaw having the largest area among a plurality of flaws is considered as a single flaw and a result obtained by replacing a plurality of flaws with penetration flaws corresponding to the plurality of flaws and calculating a collapse load are compared with each other and the smallest collapse load is set to be a collapse load of a structure.

Abstract: An object of the invention is to provide a simple method and apparatus for evaluating a collapse load of a structure with respect to ductile fracture in the case where a plurality of flaws exist in a cylindrical structure that receives a bending load. The invention is an evaluation method and apparatus in which a result obtained by calculating a collapse load while a flaw having the largest area among a plurality of flaws is considered as a single flaw and a result obtained by replacing a plurality of flaws with penetration flaws corresponding to the plurality of flaws and calculating a collapse load are compared with each other and the smallest collapse load is set to be a collapse load of a structure.

Abstract: 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.

Abstract: A method for improving residual stress of a structure member, comprising steps of: disposing coolant vessels around a pipe being the structure member at an upstream position and a downstream position of a welded portion of the pipe; wrapping a heat insulation member around an outer periphery of the pipe at a center portion in an axial direction of the pipe in each of the coolant vessels; forming the ice plug in the pipe at each position disposing the coolant vessels by cooling an outer surface of the pipe wrapping the heat insulation member in the coolant vessels; and freezing water between the ice plugs in the pipe by cooling the outer surface of the pipe between the ice plugs.