Deformation behaviour of large, high-pressure vessel flanges

The analysis of the deformation behaviour of large high-pressure vessel flanges poses a much more difficult problem than for low-pressure flanges due to their particular geometry. The narrow flange faces cause the gasket reaction moments to be relatively large as compared to the bolting moment, thereby requiring an exact knowledge of the radii of application of these reactions. The general problem of the elastic analysis of such flanges can be solved by a schematization of the flanges by perfectly rigid rings joined to cylindrical and spherical shells. Recently this approach was further refined with respect to the influences of local gasket geometry, bolt behaviour and gasket closing and opening mechanism. However, none of these approaches has taken into consideration the detailed effects of plastic deformation of the gasket faces. Furthermore, experimental information obtained on full-scale reactor vessels indicates that the approximation of the flange rings may lead to erroneous results when coupled to the assumption of purely elastic behaviour of the gasket faces. This paper supplies information on these latter subjects. Results obtained indicate that for high-pressure flanges of the narrow design investigated here the deformation behaviour is best described by an elasto-plastic finite element analysis. Where the rigid ring concept is retained for practical purposes a correction factor for local plastic behaviour of the gasket faces is suggested. (Auth.)