Applicability of ASME Code, Section XI to Flaw Evaluation of Pipe-to-Elbow Welds

Abstract Pipe-to-elbow welds in nuclear power plant piping systems are susceptible to cracking due to stress concentrations and geometric discontinuities. The flaw evaluation methodology in ASME Code, Section XI, Appendix C, designed for straight pipes, is applied to pipe-to-elbow welds without modification, potentially neglecting their unique deformation characteristics. This study evaluates the applicability of ASME Code, Section XI assumptions to pipe-to-elbow welds by analyzing key parameters such as Net-Section-Collapse (NSC) load and the Z-factor. The investigation into NSC load considered geometric factors including pipe radius-to-thickness ratio, flaw location (intrados and extrados), and flaw size, while also assessing the effects of geometric nonlinearity through comparative small and large deformation analyses. The study evaluated the applicability of the existing Z-factor, originally developed for straight pipes, to flaws in pipe-to-elbow welds. Allowable flaw sizes for pipe-to-elbow welds and straight pipes were compared for a limited set of cases. The findings highlight the limitations of applying straight pipe solutions to pipe-to-elbow welds and provide valuable insights for improving flaw evaluation accuracy in pipe-to-elbow welds.