Bolted flange joints are widely used in the fossil and nuclear power plants and other industrial complex. During their assembly, it is extremely difficult to achieve the target bolt preload and tightening uniformity due to elastic interaction. In addition to the severe service loadings the initial bolt load scatter increases the risk of leakage failure.

The objective of this paper is to present an analytical model to predict the bolt tension change due to elastic interaction during the sequence of initial tightening. The proposed analytical model is based on the theory of circular beams on linear elastic foundation. The elastic compliances of the flanges, the bolts, and the gasket due to bending, twisting and axial compression are involved in the elastic interaction. The developed model can be used to optimize the initial bolt load tightening to obtain a uniform final preload under minimum number of tightening passes. The approach is validated using finite element analysis and experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joint.

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