Optimum local failure model of steam generator tubes with multiple axial through-wall cracks

It is commonly required that steam generator tubes wall-thinned in excess of 40% should be plugged. However, the plugging criteria are known to be too conservative for some locations and types of defects and its application is confined to a single crack. In the previous study, a crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed and a coalescence evaluation diagram was developed which can be used to determine whether the adjacent cracks detected by NDE coalesce or not. In this paper, a total of 9 local failure models including flow stress model, necking-based model, stress-based model, reaction force model and plastic zone contact model were introduced to determine the optimum local failure model. Plastic collapse tests and finite element analyses using thin plates with two collinear through-wall cracks were performed for the selection of the optimum local failure model. By comparing the test results with the prediction results obtained from local failure models, the reaction force model and plastic zone contact model were determined as the optimum local failure models.