When local wall thinning damage (including through-wall) caused by erosion, corrosion and other local deterioration mechanisms is detected in pressure vessels, repair method called “Fillet Welded Patches” is often applied to them for recovering their reliability. However, it does not appear that the acceptance criteria, such as “dimension of fillet weld throat”, “wall thickness of patch plate” and “overlap length between patch and base metal”, on this weld repair method are clearly confirmed. So, this sort of repair method has not been authorized in Japan. Therefore, finite element method (FEM) analysis was used to calculate and evaluate stress and stress distribution around fillet welded patch to confirm the acceptance criteria for these important factors. In addition, accuracy of the FEM was also verified by comparing stresses and its distribution calculated by means of the FEM analysis and those obtained from pressure test.

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