Probabilistic design of structures (use of the rule R6) design of pressure vessels

This paper describes the different stages of a probabilistic approach which can evaluate the probability of failure in a mechanical structure. The process is illustrated by the example of a pressure vessel. For this type of structure, two cases are feared: leakage and bursting. The imagined failure scenarios would be the breaking down of the plastic and the spreading of a flaw. The explicit expressions of these mechanical models necessary for a reliability analysis, have been determined by two approach. First, by the English regulations for defect assessment: procedure R6 (first produced by the Central Electricity Generating board (CEGB) in 1976. It is now maintained by Nuclear Electric Ltd), second, by a simplified method of calculating J, named J8 (developed by R. Roche at the CEA/Saclay in 1987). We compare these results with the results got by finite elements. Then, we compare the admissible vessel pressure allowed by a probabilistic approach and a deterministic approach used at the CEA/DAM. (author)