Computation of leak areas of circumferential cracks in piping for application in demonstrating leak-before-break behaviour

This paper presents a simplified engineering method to evaluate lower bounds of leak areas for circumferential through-wall cracks in view of their application in demonstrating the Leak-Before-Break behaviour of pipes. Starting from the simple elastic solution in a flat plate, bulging and plasticity correction factors are applied to determine leak rates in pipes. An amplification factor due to bulging is based in Sanders' shell solutions while, for plasticity, the Dugdale-Barenblatt model is used, introducing the reference-stress concept. The method is thus applicable for a large range of diameter-to-thickness ratios and for non-uniform applied loading situations. The method is tested against a number of results obtained either numerically (finite-elements analysis) or experimentally. The results are also compared with other known simplified methods used in the USA and FRG. The simplified approach presented here, to evaluate the crack leak areas in circumferential through-cracks, has been validated on a large range of diameter-to-thickness ratios and for non-uniform applied loads. The method seems promising for demonstration of Leak-Before-Break behaviour of pipes. (orig.)