Proposal of New Code Case for Alternative UT Flaw Evaluation and Acceptance Criteria of Subsurface Flaw Near Component Surface in Section VIII Division 2 and Division 3

The current proximity rules for subsurface flaws near the surfaces of component in Section VIII Division 2 and Division 3 are different from those of Section XI. The current acceptance criteria of Sec. XI were revised in 2008 in order to eliminate the discontinuity of acceptable and unacceptable flaws based on the research work by Dr. K. Hasegawa and Dr. K. Miyazaki el. The fracture mechanics evaluation for the current and proposed alternative acceptance criteria for subsurface flaws near a component’s surfaces based on Section XI have been performed. The stress intensity factors for transformed surface flaws of the current acceptance criteria for subsurface flaws near component’s surfaces are much larger and too conservative compared with the overall acceptance criteria. It is confirmed herein that the proposed alternative converting rules have enough fracture margin. Therefore, the safety level of this proposal is almost the same as that of the current code. The proposed alternative acceptance criteria may avoid unnecessary weld repairs, and eliminate the discontinuity of acceptable and unacceptable flaws in the area near the component’s surface.