When nonplanar flaws are detected in a component they are subjected not only to fracture mode I but to fracture modes I, II and III according to the direction of the load relatively to that of the flaws. Those fracture modes are induced by the relative displacement of crack faces as they are subjected to multi-axial loading. Consequently, the Stress Intensity Factors (SIFs) KI, KII and KIII corresponding to each of those modes should be accounted for in the flaw assessment. This is done in some Fitness-for-Service Codes that make provision to calculate an effective SIF.

In the ASME B&PV Code Section XI, a simplified approach is proposed: a nonplanar flaw is resolved into two planar flaws by projection of the flaw area into the planes normal to the maximum principal stresses. This approach allows simplifying the flaw assessment procedure as it deals only with KI SIF for which a lot of tabulated or closed-form solutions exist. However, the authors of this paper demonstrated recently that this simplified resolution of nonplanar flaws is not conservative for all types of loading and flaw inclinations. Consequently, an improvement of the resolution of nonplanar flaws must be provided in ASME B&PV Code Section XI.

In that frame, this paper carries out an exhaustive assessment of the conservatism of the ASME approach and then proposes an alternative approach to deal with nonplanar flaws allowing to overcome the non-suitability of the current ASME Code.

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