| 摘要 |
PURPOSE:To reduce residual stress by the tensile stress owing to shrinkage and prevent the occurrence of cracking by fixing both side parts of the weld zone of a piping and cooling the weld zone or near the same. CONSTITUTION:Both sides of the weld zone 2 of a piping 1 are fixed with ligs 5, 6, so that the distance between the jigs 5, 6 is maintained constant. Next, a cooling tank 3 is provided to the weld zone 2, and low temp. liquid 4 is passed to maintain the weld zone 2 at cryogenic temps. Then, shrinkage by cooling takes place, but since both sides are held fixed, tensile stress is exerted upon the weld zone 2, and residual stress is decreased. For materials such as carbon steels or low alloy steels of which the yield strength increases considerably at low temps., the weld zone 2 is not cooled, and cooling tanks 3' and 3'' are provided on both sides of the weld zone 2. Low temp. liquids 4', 4'', are passed thereto to apply the tensile stress by shrinkage upon the weld zone 2 of relatively high temps., whereby the residual stress of the weld zone 2 is reduced. |
