Coalescence pressure evaluation of multiple through-wall cracks in steam generator tube using elastic-plastic finite element analyses

During an in-service inspection, if multiple cracks have been found in a nuclear component, the crack interaction effect due to adjacent cracks should be taken into account to characterize the detected multiple cracks into equivalent single combined crack or independent single crack. However, there must be many factors to be considered to quantify crack interaction effect, many experimental and numerical works should be made to propose robust guidelines on crack interaction effect depending on material characteristics of interest. Although many works have been made during the past few years to evaluate crack interaction effect of steam generator tubes with multiple cracks, the robust guidelines are still lacking. In this study, systematic 3-dimensional (3D) elastic-plastic finite element (FE) analyses are performed for steam generator tubes with multiple through-wall cracks. As for geometries of multiple through-wall cracks, four different cases are considered; axial collinear cracks, axial parallel cracks, circumferential collinear cracks, and circumferential parallel cracks. The geometric variables affecting the P_c (coalescence pressure), i.e. crack length and distance between multiple cracks, are systematically varied in the present study. Based on the coalescence pressure evaluation model proposed by authors in the previous study and the present FE results, the P_c of steam generator tubes with multiple cracks are investigated..