Liquid leakage through a rough contact: application to the internal sealing of valves

Internal sealing of valves used in nuclear power plants is performed by direct contact between metallic surfaces. In this context, this work deals with the study of liquid leakage through a tight contact between two rough surfaces. Two approaches were followed in parallel: a theoretical/numerical one and an experimental one. Models developed here allow to predict leakage as a function of tightening starting from non-deformed textures of contacting surfaces. Surface deformation is first computed with a semi-analytical elasto-perfectly plastic model. Liquid flow is then solved through the resulting aperture field. Models for characterizing and synthesizing roughness were also developed from fractal theory, providing a complete numerical tool for leakage predictions. From these models, a correlation between surface textures and sealing efficiency was established. Moreover, leak-rate measurement were carried out to test the model performance. Direct comparisons between experimental results and simulations showed that predictions over-estimate the leak-rates, especially when tightening is high. A detailed analysis of the whole calculation procedure showed that deviations mainly originate from the deformation model. Improvement of the predictive tool might require the consideration of material heterogeneity at the constitutive grains. (author)