The fitness-for-service codes such as the ASME Boiler and Pressure Vessel Code Section XI require the characterization. of non-aligned multiple flaws for flaw evaluation, which is performed using a flaw alignment rule. Worldwide, almost all such codes provide their own alignment rule, often with an unclear technical basis regarding the application of the rule to plastic collapse due to ductile fracture as prescribed by limit load analysis based on a net-section approach. Therefore, evaluation procedures to calculate collapse load for non-aligned multiple flaws have been proposed in various experimental and analytical studies. In these proposals, a collapse load for nonaligned multiple flaws is evaluated using the net-section stress approach in consideration of the ratio of a distance between flaws to a flaw length parameter. However, because each study proposes its own appropriate length and distance parameters, which are based on a few experimental results limited to that study, the applicability of the proposed parameters to evaluation of collapse load for arbitrary flaw sizes and locations is unclear. In this study, we performed fracture test result on a flat plate with two through-wall flaws in order to determine appropriate parameters for the evaluation procedure of the collapse load for non-aligned multiple flaws. Appropriate parameters were determined by correlation coefficients obtained by comparison of maximum loads of fracture tests and collapse loads of evaluation with various parameters. We found that the appropriate parameters to apply the alignment rule with equations to evaluate collapse load for non-aligned flaws were the ratio of the vertical or direct distance between flaws to the maximum or average flaw length.
