Alignment Rule for Non-Aligned Flaws for Fitness-for-Service Evaluations Based on LEFM

If multiple discrete flaws are detected that are in close proximity to one another, alignment rules are used to determine whether the flaws should be treated as nonaligned or as coplanar. Alignment rules are defined in many fitness-for-service codes and standards in the world. However, the criteria of the alignment rules are different in these codes and standards. This paper introduces the current alignment rules and, in addition, interaction of stress intensity factors for nonaligned through-wall flaws was calculated by finite element analysis. Also, brittle fracture experiments were performed on carbon steel plates with two nonaligned flaws. From these calculations and experiments, authors studied the effect of stress intensity factor interaction on fracture behavior and proposed a new alignment rule for linear elastic fracture mechanics evaluation.