Very Low Cycle Fatigue Evaluation of Pipe Elbow Test Under Quasi-Static Loading

Abstract The International Atomic Energy Agency (IAEA) emphasizes that the structural integrity of critical safety equipment and facilities must be ensured under both design-basis and beyond-design-basis earthquake. For ensuring structural integrity against earthquakes, it is crucial to apply elastic-plastic fatigue analyses. In this study, elastic-plastic fatigue analyses were conducted on 90-degree elbows using the method proposed in ASME Code Case N-900, JSME NC-CC-008, and ASME Section VIII Div.2 Part 5. The elbow test specimens were made from SA234 WPB carbon steel and SA403 WP316 stainless steel, used in primary and secondary piping systems of nuclear power plants. Quasi-static displacement-controlled cyclic loadings were applied at room and operating temperatures. To simulate the pipe elbow tests, 3D elastic-plastic FE analysis was performed using bilinear kinematic hardening model. The FE analysis was validated by comparing the reaction forces from the experiments. The evaluation was conducted using the analysis data at the damage locations, and results were compared using the defined Cumulative Usage Factor (CUF). For both SA234 WPB carbon steel and SA403 WP316 stainless steel, CUF was evaluated. As a result, the conservatism of the evaluation methods decreases in the following order: ASME Code Case N-900, ASME Section VIII, JSME NC-CC-008. The influence of internal pressure was also considered.