HEAT TREATMENT METHOD FOR PIPING

摘要

PROBLEM TO BE SOLVED: To provide a heat treatment method capable of improving the residual stress of a pipe generated by welding or processing, particularly the method in such a case where there is the possibility that defects such as crack exists in a thin small-diameter pipe.

SOLUTION: The heat treatment method includes the steps of: checking the existence of defect and measuring the dimension thereof regarding a pipe before heating; measuring the wall thickness of the pipe; obtaining the relationship between the pipe wall thickness and a target outer surface temperature-lowering speed based on a measured defect dimension and the wall thickness; installing a temperature-measuring instrument on the pipe outer surface of a targeted position for heat treatment; installing a heater to a targeted part for heat treatment; heating the pipe using a heat-treating unit, so that the temperature of the instrument becomes a target level; quickly cooling the inner surface of the pipe by streaming a coolant after reaching the target temperature while measuring the change with time of the outer surface temperature using the instrument; and evaluating whether construction is adequate or not from the standpoints of the measured wall thickness and the outer surface temperature-lowering speed after completion of water circulation.

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