Abstract: A method for improving a residual stress in a pipe includes improving the residual stress in the inner surface to the compressive direction by rapid cooling of the inner surface after heating of the pipe. The heating is to heat a vicinity of a welded part of the pipe from the outer surface to raise the temperature to a construction temperature. The rapid cooling is to rapidly cool the inner surface in the vicinity of the welded part by supplying cooling water into the pipe. The heating and the rapid cooling are repeated twice or more. A method for construction management includes determining whether construction has been executed properly based on a maximum value of a lowering rate of an outer surface temperature of the pipe when the cooling water is supplied for the rapid cooling of the inner surface and a thickness of the pipe in a measuring position of the outer surface temperature.

Abstract: The present invention provides a heat treatment method comprising: welding a small diameter pipe (12) to a bonded joint (31) joined to a large diameter pipe (10), the small diameter pipe (12) having a diameter of 200 mm or less and a thickness of 15 mm or less, the large diameter pipe (10) having a diameter greater than that of the small diameter pipe (12); then heating the vicinity of the welded portion; and then cooling an inner surface of the pipes by use of coolant; wherein a distance between a heating area and the large diameter pipe (10) is equal to or greater than 70 mm. The heat treatment method can reduce the intention residual stress caused by welding or processing the pipes.

Abstract: A method for improving a residual stress in a pipe includes improving the residual stress in the inner surface to the compressive direction by rapid cooling of the inner surface after heating of the pipe. The heating is to heat a vicinity of a welded part of the pipe from the outer surface to raise the temperature to a construction temperature. The rapid cooling is to rapidly cool the inner surface in the vicinity of the welded part by supplying cooling water into the pipe. The heating and the rapid cooling are repeated twice or more. A method for construction management includes determining whether construction has been executed properly based on a maximum value of a lowering rate of an outer surface temperature of the pipe when the cooling water is supplied for the rapid cooling of the inner surface and a thickness of the pipe in a measuring position of the outer surface temperature.

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.