Theoretical analysis of leak-before-break in stainless steel pipe with a circumferential through-wall crack

Assessment of the leak before break (LBB) condition is a crucial problem with regard to the structural integrity of nuclear piping system which might be degraded by the occurrences of stress corrosion cracking. In this respect, the authors derive the condition for unstable fracture of pipes with a circumferential through-wall crack based on the simplified method, which is used to examine the LBB condition under the real plant conditions. This report consists of the following two parts: 1) After the verification of the simplified method by the comparison of its predictions with the experimental results, it is applied to the calculation of the critical crack lengths for unstable fracture. 2) Critical crack lengths for leak detection are compared with those for unstable fracture to examine the margin for the leak before break. From this comparison, it is proved that the leak before break may arise with a condisereble margin under the applied stress, compliance and pipe configuration conditions of real plants. (author)