Finite Element Plastic Limit Loads of Complex Cracks in Pipes With Two-Layered Materials

Based on the detailed three-dimensional (3D) finite element (FE) limit analyses, the present study investigates the plastic limit loads of complex-cracked pipes with two-layered materials for determining maximum load-carrying capacity or critical crack length of pipes with two-layered materials. The complex cracks in pipes with two-layered materials consist of a partial through-wall crack and 360-deg circumferential surface crack in the inner side of pipe in the same plane in pipe, which could be developed in the preemptive weld overlay region on the dissimilar metal weld (DMW) of nuclear pipe. In terms of FE limit analyses for complex-cracked pipes with two-layered materials, total thickness of pipe, depth of 360-deg internal surface crack, length of partial through-wall crack and the effect of strength mismatch between two materials are systematically considered in the present study. As for loading conditions, axial tension, global bending moment, and internal pressure are employed in the present FE analyses, and then, the confidence of the present FE procedure is confirmed by comparing the FE results with the existing solutions for complex cracks in single material. The results of the present FE plastic limit loads are compared with the existing solutions for complex-cracked pipes with two-layered materials. Also, a simple approach using equivalent single material based on the weighted average concept instead of using the properties of two materials is suggested for predicting plastic limit loads of two-layered materials. The present results can be applied to leak-before-break (LBB) analyses of nuclear piping with weld overlay.