Abstract
The main purpose of this study is to ensure the structural integrity of power plants. The accidents of SCC (Stress Corrosion Cracking) at the weld region of the coolant pipe of nuclear power plant are reported at domestic and foreign countries. Since welding residual stress is one of the main factors of the phenomenon, understanding the welding residual stress distribution is important in the estimation of plant life cycle and maintenance. However, the residual stresses of the weld joint have complex distributions three-dimensionally. In this study, the inherent strain method combined with FEM (Finite Element Method) is applied to measure the welding residual stress distribution accurately.
The pipe girth weld mock up was used in this study. As the mock up model was axial-symmetrical shape, the new theory of inherent strain method for the axial-symmetrical model was developed. The FEM program was also prepared based on the theory. Measuring the relaxed strains by cutting the model, the residual stresses distributions were analyzed by the FEM program.
The inherent strain method gives the most probable values and the deviations of the residual stresses simultaneously. Around the middle of the weld center section, the axial stress value is small, but the circumferential stress is estimated to be large tension. Evaluating the analyzed results, the deviations are small enough for the most probable values. Moreover, the feature of the stress distributions fundamentally corresponds with the ones obtained by the thermal elastic-plastic analyses. Therefore, developed measuring method for axial-symmetrical model shows high reliability.
