If the relationship between the defect size and the fracture strength of welded joint is made clear, the permissible level of the defect size to secure the performance required by the design is grasped, and it is useful for the admission decision with the defects which is detected by the ultra sonic test. In this paper, the fracture strength of welded joints with weld defects is discussed. In order to grasp the permissible level of the defect size of welded joint, the investigation about the results of the previous studies was carried out and the construction of the estimated equation of the fracture strength by application of linear fracture mechanics was attempted. As the results of this study, the estimated equation was proposed.
