Comparison of K-Solutions of Rectangular Flaw With Semi-Elliptical Flaw for PWSCC Growth Analysis

Abstract The JSME Codes and Standards has a Code Case of K-solutions of a rectangular flaw for primary water stress corrosion cracking (PWSCC) growth analysis. The shape of axial PWSCC flaws in a dissimilar material weld (DMW) joint is relatively rectangular rather than semi-elliptical. This flaw will propagate selectively in the weld metal, which makes it a deep, short flaw. The K-solutions of the JSME Code Case have been provided considering the features of the PWSCC flaw conservatively. The same K-solutions for a Code Case of ASME Section XI were proposed and have been discussed in a Working Group of the ASME Sec. XI Standard Committee. In the Working Group, sample problems were proposed to confirm necessity of introduction of K-solutions for a rectangular flaw into the ASME Code, and the appropriateness of the code description of a draft Code Case based on the JSME Code Case. Especially, there was a discussion to avoid over-conservatism of the K-solution. In the sample problems, the K-solutions, that is Gi coefficients, of a rectangular flaw and a semi-elliptical flaw were compared for various 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, up to the ratio of 0.5 to 0.6. Also, PWSCC propagation calculations of both types of the flaws assumed in a DMW joint of a primary coolant pipe with double V groove, a hot leg with single V groove and a surge line with single V groove were performed by using the K-solutions of a rectangular flaw and a semi-elliptical flaw. These Code basis calculation results were compared with the result of the 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. The initial semi-circular flaw grew with a semi-elliptical shape and the initial rectangular flaw grew with a rectangular shape. 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. Based on the results of the sample problems, the code description of the Code Case was revised.