The two essential elements of a leak-before-break case for a piping system are: (a) The size of through-wall circumferential crack that gives a measurable leakage under normal operating conditions, and (b) The size of through-wall circumferential crack that is unstable under accident conditions. The procedure for estimating these sizes is based on calculating the stresses at the assumed crack section via a purely elastic analysis for the system, but assuming that the system is in fact uncracked. However because a piping system is built-in at its ends into some larger component, and because the crack's presence is associated with an effective kink at the cracked section, this procedure is conservative with regard to the critical unstable crack size but is non-conservative with regard to the critical leakage crack size. The paper reviews the author's research on the problem and concludes that the conservatism with regard to the unstable crack size is over-riding so that, overall, the procedure should be conservative.
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