3-D FE analyses of WRS and simplified elastic-plastic fracture mechanics assessment of a repaired weld

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Abstract An effective excavation and re-welding process is often needed to correct the installation slope and geometric misalignment in the piping, where significant local plastic strain damage and complex welding residual stresses (WRS) often occur during the repair process. At the same time, it is complex to perform elastic-plastic fracture assessment for combined loads such as the WRS, bending moment and internal pressure. In this paper, three-dimensional (3-D) finite element (FE) analyses of WRS of the repair welding are performed, and the influence of weld bead sequencing as well as the displacement caused by external loads is simulated. In the study, the plastic strain damage is also assessed to prevent void formation. To avoid the complex elastic-plastic fracture assessment, a simplified elastic-plastic fracture study is carried out based on the failure assessment diagram (FAD) method. The results show that the repair process is effective, and the strain damage caused by the weld repair is acceptable. There are clear differences between WRS caused by initial weld and that of the re-weld, and there is palpable influence of the repair process on the WRS for the unrepaired/unexcavated part of the pipe. Based on the simplified elastic-plastic FAD method, the repair process has obviously influence on the margin of safety. The repair process described in this paper is generic and thus can be applied in similar pipe deflection correction applications.