다중 관통균열이 존재하는 증기발생기 세관의 최적 국부파손모델 결정

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 base model, stress base model, reaction force model and plastic zone contact model were introduced to determine the optimum local failure model. Plastic collapse tests and FEA using the plate 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, reaction model and plastic zone contact model were determined as the optimum local failure models.