Non-linear elastic-plastic techniques have been used to study the level A operating conditions of a relief valve subject to a small number of severe thermal shock transients during operation. The analysis uses a detailed FE mesh verified to capture the elastic-plastic behaviour of the valve. In addition, short duration transient heat loading on the valve was calculated using computational fluid dynamics using a conjugate heat transfer approach.

The non-linear plasticity behaviour of the model was simulated using a kinematic hardening model incorporating non-linear hardening. Due to the very localised plasticity around small radius fillets in the model, a highly refined mesh strategy was needed. An innovative meshing strategy was therefore incorporated utilising a similar methodology to that used for fluid dynamics meshing; the fluid facing surfaces and nozzles were finely meshed with hexahedral elements, while parts of the internal bulk material were meshed using high order tetrahedral elements.

Primary strength was analysed using traditional elastic methods. The progressive distortion check was based on the elasto-plastic through-wall strain distribution and the fatigue analysis based on the equivalent strain range.

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