CHARACTERIZATION OF LEAKAGE THROUGH GASKETS BY A TWO-STAGE NUMERIC APPROACH USING TRANSPORT EQUATIONS

The present discussion on environmental impact leads to the need to reduce fugitive emissions in the processing industry. In Europe, the IPPC requires national governments to put standards such as VDI-guideline 2290 [1] - into place that force plant operators to meet the best available techniques. In this study, an approach is presented, to estimate the effects of inhomogeneous gasket stresses, geometry changes and combinations of different gasket materials to improve the sealing performance and reduce fugitive emissions. Compression and leakage tests according to DIN EN 13555 [2] formed the basis to characterize the gasket pressure-closure behaviour and permeability of a homogeneous stressed sheet gasket material. Provided that linear pressure dependency is applicable, transporttheory according to heat conduction can be applied to calculate the effects of inhomogeneons gasket stress distribution or variation of gasket geometry such as gasket width. The method implies a two-stage procedure. In the first step, the local gasket stress distribution and thus the corresponding permeability in a flange connection is calculated. The local permeability is allocated for each element in terms of a unique material definition. Solving the steady state in the second step under inner and ambient pressure-constraint leads to the internal pressure distribution, local leakage flow and the overall leakage rate. The approach is applied and verified at an inhomogeneous stressed sheet gasket and enables us to predict the reduction in the leakage rate by factor 3000 of an prestressed PTFE-sheet gasket due to the decreased gasket width.