3D micro-macro fluid-structure model of pressure relief valve leak tightness

Controlling and assessing the leak tightness of a Pressure Relief Valve (PRV) has been a challenge since the original design of the product. With more stringent demands from the nu- clear power industry for leakproof PRV’s, closer to the set point, there has been a drive by both industry and academia for a better design method for many known metal-to-metal contacting seal/surface problems. This paper outlines a numerical modelling strategy drawn from industry experience and metrology measurements and investigates the effects of lapping and surface finish on leakage rate. Key influencing parameters of surface form, waviness and roughness are incorporated in the analysis. The numerical approach requires efficient coupling of a non-linear structural Finite Element Analysis (FEA) with a Computational Fluid Dynamic (CFD) solver. This allows the examination of the relationship between deformation of the contacting surfaces, based on the applied spring force, and the resulting micro-flow of gas through any available gaps and the overall leakage to be found. The API527 Seat Tightness methodology is followed to allow leakage rates to be measured and the computational model to be preliminarily validated. Using this model, engineers can adjust and optimise the design of pressure relief valves to find the minimal leakage condition for a given configuration. In addition, the numerical approach can potentially be applied to other metal-to-metal contacting surface components, such as flanges with metal gaskets, and help eliminate leakage.