Metallic gasket sealing connections are widely used in pressure vessels and piping.The failure of most sealing systems is caused not by the strength of flanges but by the leakage of the connections.Based on the leakage model of metallic gaskets the effect of the non-uniform distribution of the contact stress of gasket on the shape and size of the leakage passage was investigated

and the equation for calculating the leakage rate of the sealed medium flowing through a leakage passage with variable cross-section was derived.Such an equation described the relationship among the leakage rate of the connection，the contact stress of gasket，the medium pressure and the fractal parameters of the sealing surface.The research results make it possible to design the metallic gasket connections based on the criterion of the maximal allowable leakage rate and to assess the tightness of the connections.