FEM Automatic Crack Propagation Analysis System for Nuclear Power Plant Using Provided Welding Residual Stress and Its Verification Test

A developed crack propagation analysis system using the finite element method for components like vessels and pipings in nuclear power plants is described. One of the characteristic features of the system is that its input data include welding residual stresses and the stresses produced by applied forces in the components which have been obtained from previous analyses. In the system, the nodal forces on the crack surface are calculated from these input stresses. The authors extended the Virtual Crack Closure-Integral Method so as to calculate stress intensity factors when nodal forces on crack surface exist and applied the method to the system. In order to set test analysis problems for the system, conditions were found in which an elliptical crack holds the elliptical shape in fatigue crack propagation, and accordingly the crack size changes can be predicted using the theoretical stress intensity factors for an elliptical crack in infinite bodies subjected uniform tensile stresses. Under these conditions, a test analysis was carried out using the system, and the obtained crack size changes were shown to be in good agreement with those obtained from the theoretical stress intensity factors. As an example problem for practical structures, crack propagation due to SCC in a cylinder with a residual stress distribution solved by the system are presented and the results are compared with reliable reference values calculated using stress intensity factor data in a literature.