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Investigations on Leak-Before-Break (LBB) analysis

Mansoulié, Christophe

[Thesis]. Manchester, UK: The University of Manchester; 2010.

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Abstract

The present thesis was written by Christophe Mansoulié at the University ofManchester in pursuance of the degree of Master of Philosophy. It presents“Investigations on Leak-Before-Break (LBB) analysis” performed within the programof the British safety insurance company Serco to assess more complex Leak-Before-Break cases. Proceedings of British defect assessment code R6 on LBB analysis aresummarised, and then the main focus is made on the computation of crack openingareas (COA) and stress intensity factors (SIF) for cracks in pipes and pressure vessels.A general overview of these methods is presented, and a comparison between twocodes is made with regard to the numerical computation of SIF. The influence of thethermo-mechanical coupling of the structure with the fluid is investigated usingenhancements of numerical tools from the French company EDF, concluding to apossible significant change in flow rates found. From there general theoreticalmethods to analyse linear thermo-elastic fracture mechanics problem are considered,and in particular a simpler thermo-mechanical model of an infinite plate containing acrack subjected to uniform heat flux. An application of crack opening area calculationis made for this case, and difficulties of modelling in thermo-elastic fracturemechanics are raised. In the scope of Serco’s program also including the assessmentof complex geometries, a numerical investigation of one typical example of their effecton COA and SIF is performed in the case of continuous thickness transitions in pipes,for which a shielding effect is brought to light.