Effect of nozzle geometry on leak-before-break analysis of pressurised piping

This paper reports the effect of a through-wall crack at the thickness transition near the pipe-nozzle interfaces on the leak-before-break (LBB) analysis. Two pipe-nozzle models are considered, a safety injection line and a pressurised surge line. Based on detailed three-dimensional, elastic-plastic finite element analyses, the effect of the thickness transition on the J-integral and the crack opening area (COA) is elucidated by comparing the results with those from a straight pipe model. To investigate the overall effects of the thickness transition on the LBB analysis, piping evaluation diagrams are constructed. Further analyses are performed to investigate the effect of the detailed nozzle geometries on the COA, to provide guidance on simplifying the LBB analysis for the pipe-nozzle models. It is found that the regions for feasibility of applying the LBB concept are 30-190% larger when the thickness transition in the pipe-nozzle model are explicitly considered in the analysis, than when the straight pipe model is used. Among the parameters related to the shape of the nozzle geometry, the thickness of the pipe-nozzle junction is the most significant parameter on the COA, but the length of the nozzle has a minimal effect. The significance of the tapered angle between the pipe and the nozzle is somewhat in between.