Instability Moment Predictions for Complex Through-wall Cracked Pipes of Low Alloy Steel

The complex through-wall cracks (TWC) that have been discovered in the dissimilar metal weld of nuclear power plants have different fracture behavior compared with the simple TWC that is typically assumed in a flaw evaluation. In this regards, a number of prior research has aimed at developing an appropriate J-estimation scheme and constructing of the J-R curve that can be utilized for complex crack analysis. In the present paper, instability moments of complex TWC pipes of low alloy steel were calculated through the crack driving force diagram approach, employing J-estimation formula for complex crack recently developed. As a fracture property, the test data of complex crack tension (CCT) specimen was used. Comparing with the prediction results of FE analysis using a damage model, it was observed that this procedure could provide an accurate prediction of the instability moment with the reasonable conservatism.