Comparison of <i>K</i>-solutions of rectangular flaw with semi-elliptical flaw for PWSCC growth analysis

The shape of axial primary water stress corrosion cracking (PWSCC) flaws in a dissimilar material weld (DMW) joint is relatively rectangular rather than semi-elliptical. The K-solutions for a rectangular flaw as a PWSCC flaw for a Code Case of ASME Section XI were proposed in the ASME Sec. XI Standard Committee. During the discussion in a WG of the Code Committee, sample problems were proposed to confirm necessity of K-solutions for a rectangular flaw. In the sample problems, the K-solutions, that is Gi coefficients, of a rectangular flaw and a semi-elliptical flaw were compared for flaws with a different flaw depth and length. The deeper and the narrower the flaw, the larger the difference of the Gi coefficients between a rectangular flaw and a semielliptical flaw. Also, PWSCC propagation calculations of both types of the flaws assumed in a DMW joint of a pipe with double V groove, with single V groove or with single V groove were performed by using the K-solutions of a rectangular flaw and a semi-elliptical flaw. It was assumed that the initial semi-circular flaw grew with a semi-elliptical shape and the initial rectangular flaw grew with a rectangular shape. These calculation results were compared with the result of Advanced FE (AFEA) analyses which simulated actual axial flaw growth behavior. In the sample problems, the initial flaw was a semi-circular flaw within a weld width or a rectangular flaw with a length of the weld width. As a result, the calculation results of semi-elliptical flaws were quite similar to those of AFEA. The condition of a rectangular flaw with the initial flaw length of the weld width was too conservative, which was in the code description of the first draft Code Case. If the initial semi-circular flaw reached the weld boundary at the surface point and changed to a rectangular flaw, the PWSCC propagation behaviors were reasonably conservative. The results of the sample problems were reflected to the draft Code Case, which was approved by the Standard Committee of ASME Section XI on January 2025.