APPLICABILITY OF ASME CODE, SECTION XI TO FATIGUE CRACK GROWTH CALCULATION OF FLAWS IN PIPE-TO-ELBOW WELDS

The American Society of Mechanical Engineers Boiler & Pressure Vessel (ASME B&PV) Code Section XI provides procedures for fatigue crack growth calculation which can be used for flaw evaluations. However, the solutions in ASME B&PV Code Section XI are for straight pipes, making it potentially unsuitable for evaluating flaws at pipe-to-elbow welds. To address this limitation, the stress field at the pipe-to-elbow weld cross-section is used in the straight pipe solution to calculate the stress intensity factor for crack growth calculations. This feasibility study aims to verify the accuracy of ASME B&PV Code Section XI procedure in predicting circumferential fatigue crack growth in actual pipe-to-elbow configurations. For this purpose, a natural crack growth simulation program based on finite element analysis using adaptive meshing was used to perform the verification. The reliability of the program was first established by comparing its stress intensity factor calculations with those obtained from ASME B&PV Code Section XI procedure for various flaw geometries in straight pipes. Subsequently, natural fatigue crack growth calculations were performed for circumferential flaws in pipe-to-elbow configurations. These results were compared against ASME B&PV Code Section XI results using the pipe-to-elbow interface stress fields. Comparisons were made for various pipe-to-elbow configurations, loading, and two different initial crack sizes.