Abstract
Post-welding heat treatment (PWHT) is carried out on 2.25Cr–1Mo steel used in pressure vessels, to relieve welding residual stress and diffused hydrogen and to soften the weld joint. However, it is known that reheating cracks often occur during PWHT. A standard specimen is available to pre-estimate the existence of cracks in pressure vessels according to rules such as those in Japanese Industrial Standard WES 3005. However, these specimens do not reflect the shape of the pressure vessels and do not reproduce the actual cracks correctly because of non-cylindrical welding. In the present paper, a numerical analysis has been conducted for various models, which can reproduce the occurrence of reheating cracks in the welded joint of a pressure vessel nozzle. The present paper also investigates mechanical behaviour such as the relief history of welding residual stress as well as the accumulated history of creep strains. Through the above processes, the mechanical behaviour of the welded pressure vessel nozzle joints has been elucidated and a model of reheating crack initiation has been selected. In addition, experiments on reheating crack initiation have been carried out for the WES 3005 specimen, and a new susceptibility assessment specimen has been proposed and developed to pre-estimate the existence of actual reheating cracks correctly.
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