Probabilistic Modular Tool to Assess Leak Before Break in Pipes

Abstract

This paper presents the probabilistic study for Leak Before Break (LBB) assessments. The research has been carried out with an in-house developed software that allows to perform both probabilistic and deterministic leak before break analyses for pressurized pipes. The study is based on the UK procedure for the assessment of the integrity of structures containing defects (R6). The procedure applied is the Detectable Leak Before Break (DLBB) that relies on the Failure Assessment Diagram (FAD) Option 1 assessment procedure. The calculations merge the plastic collapse assessment and the brittle failure mode of the pipe in the FAD. The first computed parameter for the LBB assessment is the Critical Crack Length (CCL) distribution density of the postulated through wall defect. The structural integrity assessment is then coupled with the Henry-Fauske two-phase critical flow model for the evaluation of the Leakage Rate (LR). With this coupling the Minimum Detectable Crack Length (MDCL) distribution density is calculated. This step sets the boundary conditions for the fracture mechanics assessment of the postulated defect. The main probabilistic outputs from the assessment are the probability of the structural failure and the probability that the defect does not leak a detectable amount of coolant. The probabilistic method used is the Latin Hypercube Sampling; the Monte Carlo method is applied for verification. These results are then compared with the deterministic output from the LBB procedure.