Application of multiscale approaches to the investigation of sealing surface deformation for the improvement of leak tightness in pressure relief valves

This chapter is part of a research program to investigate and model the leak tightness of a Pressure Relief Valve (PRV). Presented here is: a literature review; high temperature numerical study involving the deformation of contact faces for a metal-to-metal seal accounting for micro and macro effects; and also microscopic measurements of surface finishes and how they are modelled over a micro to nanometer scale. Currently, no review of literature exists which attempts to understand the leakage phenomenon of metal-to-metal seal contact PRV for static closed positions as they reach the set pressure point. This work attempts to do just that by drawing on inspiration from other research areas such as metal-to-metal contact and gasket seals. The key topics of interest surrounding the leakage of fluid through a gap are: fluid flow assumptions, surface characteristics and its deformation, and experimental techniques used to quantify leakage. For the numerical study, the valve geometry is simplified to an axisymmetric problem, which comprises a simple geometry consisting of only three components: a cylindrical nozzle, which is in contact with a disc (representing the valve seat on top), which is preloaded by a compressed linear spring. The nozzle-disk pair is made of the austenitic stainless steel AISI type 316N(L) steel. In a previous study, the macro-micro interaction of Fluid Pressure Penetration (FPP) was carried out in an iterative manual procedure at a temperature of 20°C. This procedure is now automated and implemented through an APDL script, which adjusts the spring force at a macro-scale to maintain a consistent seal at elevated temperatures. Finally, using the Alicona Infinite Focus the surface form and waviness is measured, presented and modelled as 1/4 symmetric over a macro to nanometer scale. It is clear the surface form also needs to be accounted for, something which the literature does not focus on.