Multipass Welding Stresses in Very Thick Plates and Their Reduction from Stress Relief Annealing

概要

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An investigation into residual stresses induced in a connection of a pressure vessel by multipass welding and their reduction by stress relief annealing was conducted. The study was performed theoretically and experimentally on idealized research models. In the theoretical analyses, the thermal elastic-plastic creep theory developed by the authors was applied and the results of the analysis show a good, fundamental coincidence with the experimental findings. The outline of the results and the conclusions is as follows. (1) The largest transverse transient stress (σ_χ) during welding always appears just below the weld metal of the newest layer. But as the layers of weld metal are piled up, this stress is relieved gradually. This implies that the application of intermediate annealing for the sole purpose on reducing welding residual stresses is unnecessary. (2) In the welding residual stress (σ_χ) distribution, the location of the largest tensile stress is just below the finishing bead. Judging from the residual stresses and available information about cracks in actual structures, delayed cracks do not initiate at the toe of weld on the surface, but do initiate several layers below it. (3) The effectiveness of stress relief annealing depends greatly on the annealing temperature in the case of comparatively low heating rate for annealing.
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