A Comparison of Failure Load Assessment Methods for Thin-Walled Tubes With Cracks

Heat exchangers in fossil and nuclear power plants comprise thousands of thin-walled tubes. Operational experience shows that cracks have been frequently detected in the tubes. Since the structural integrity of the heat exchangers is crucial from the viewpoint of safety and reliability, the integrity evaluation of the cracked tubes is quite important. The failure modes of the cracked tubes are determined herein in accordance with Section XI of ASME Code. In addition, failure loads are evaluated using various methods and compared with test data in order to determine an optimum estimation method. The analysis results show that the failure mode of the cracked tubes is plastic collapse. Also, the predicted failure loads by finite element limit analyses agree very well with the corresponding test data, whereas the analytical approaches are significantly under predictive depending on the crack type and size. It is, therefore, considered that the finite element limit load approach can be applied to the practical integrity evaluation and the establishment of an optimum inspection strategy for managing the heat exchanger tubes.