On the use of plate theory to evaluate the load relaxation in bolted flanged joints subjected to creep

The effect of load relaxation due to creep has a major impact on the tightness of bolted flanged joints. Several leak incidents have been reported in the petrochemical and nuclear power plants related to creep. It is clear that the current flange design code does not address adequately the effect of high temperature on the mechanical and leakage integrities of bolted flange joints used in pairs or with blind cover plates. It is possible to include the creep analysis in the design methodology. This paper outlines an analytical approach based on plate theory used to determine the creep effect of blind cover plates and flanges of a small size on the bolt and subsequently the gasket load relaxation in bolted flanged joints. It details the theoretical procedure to predict the creep effect of those flanges considered as plates. The results from the theoretical model are verified by comparison with 3D finite-element results