Cyclic response of enhanced bolted flange joints for piping systems

Bolted Flange Joints (BFJs) represent the most common and critical components used nearly in all industrial piping systems, including Oil & Gas plants. Owing to their strategic importance and heavy consequences both to the environment and human lives due to both damage and leakage, BFJs are considered very important in industrial plant design. Therefore, their behaviour becomes critical also under seismic actions. Along this line, in the first part of this paper the experimental test campaign performed on enhanced bolted flange joints subject to both monotonic and cyclic loading is presented and discussed. Then, specific values of both stiffness and strength with reference to leakage are estimated. Successively, a reliable model capable of predicting the leakage force for a generic BFJ, including the interaction between the axial and shear load, is proposed and validated; in particular, both actual and previous full scale experimental data were involved in the validation. As a result, the values predicted by the model agree well with those obtained by the experiments. This model is also adopted to predict leakage stiffness values for thick flanges. Overall, the proposed analytical model can represent a promising tool for the leakage prediction of BFJs in complex piping systems.