Metal to metal flanges leakage analysis

The use of a gasket made in soft material is not recommended for large size centrifugal compressor case flange. The two case halves are assembled with bolted flanges and leakage is prevented by the metal–to–metal contact under pressure. The prediction of the leakage condition is an important engineering issue for this technology. In the paper an original model able to predict the leakage condition, based on a Fracture Mechanics approach, is presented. The flange surfaces interface is regarded as a crack which can be partially open. As the flanges can not transfer tensile traction, the extension of the open zone, i.e. the crack length, is obtained by the condition that the Stress Intensity Factor K is zero. An analytical model, based on the Weight Function technique, was applied to find the stress intensity K, and then to predict the leakage condition. The paper illustrates a validation of the proposed model by the comparison with a nonlinear Finite Element analysis and the results of a full scale experimental test series obtained by a research collaboration between industry and academia. The leakage pressure predicted by the model is in good agreement with the numerical prediction and the experimental results.