Bolted flanged gasketed joints are the weak link between pressure vessel equipments including nuclear reactors. Their leakage tightness behavior is compromised due to the effect of creep of the gasket, the bolts and the flange, which relaxes the bolt load and causes a subsequent loss of the gasket contact stress. This is especially true when the joint is operating under high pressure and high temperature conditions. Apart from an acknowledgement of this affect, the ASME code does not give specific guidelines to help the design engineer in assessing this effect. The objective of this paper is to present an analytical method capable of predicting the bolt load relaxation in a gasketed joint as a result of creep of either the gasket, the bolt and the flange separately or all together. The proposed method is validated by comparison with 3D FE models of different size flanges and experimental data. A strong emphasis will be put on flange rigidity, which is the major controlling parameter of the load relaxation.

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