Adjacent multiple cracks can be found in power plant components such as pressure vessel, piping and so forth. If multiple cracks are detected, it can be affected significant effect to structure integrity due to high interaction effect of the multiple cracks. Therefore general fitness-for-service (FFS) codes and standards propose assessment method for the multiple cracks. The Section XI of ASME Code suggests crack coalescence method for multiple cracks. It employs the approach combining neighbored cracks as single crack if the distance between them is close. In some cases, since this combined rule can be considered as a conservative approach, more accurate investigation of the interaction effect between multiple cracks is needed. In this study, the interaction effect between two aligned coplanar circumferential surface cracks in elbows subjected to internal pressure was investigated. Since most previous studies dealt with only plates or straight pipes, the present research was centered on cracked elbow. FE (Finite element) limit analyses were carried out by changing elbow geometries and crack shapes. Also, applicability of the current criterion for the multiple cracks was discussed.

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