Bolted flange joints are widely used to connect pressure vessels and piping equipment together and facilitate their disassembly. Initial tightening of their bolts is a delicate operation because it is extremely difficult to achieve the target load and uniformity due to elastic interaction. The risk of failure due to leakage and fatigue under service loading is consequently increased. This paper presents a study on the effect of elastic interaction that is present during the tightening of bolted flange joints using three-dimensional nonlinear finite-element modeling and experimentation. The nonlinear nonelastic behavior of the gasket is taken into account in the numerical simulation. The scatter in bolt preload produced during the tightening sequence is evaluated. Based on the elastic interaction coefficient method, the initial target tightening load in each bolt for every pass is determined by using the nonlinear finite-element model to obtain a uniform preload after the final tightening pass. The validity of the finite-element analysis (FEA) is supported by experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joints using fiber and flexible graphite gaskets. This study provides guidance and enhances the safety and reliability of bolted flange joints by minimizing bolt load scatter due to elastic interaction.

The tightness of bolted flanged joints subjected to elevated temperature is not properly addressed by flange design codes. The development of an analytical method based on the flexibility of the different joint components and their elastic interaction could serve as a powerful tool for elevated temperature flange designs. This paper addresses the effect of the internal fluid operating temperature on the variation of the bolt load and consequently on the gasket stress in bolted joints. The theoretical analysis used to predict the gasket load variation as a result of unequal radial and axial thermal expansion of the joint elements is outlined. It details the analytical basis of the elastic interaction model and the thermally induced deflections that are used to evaluate the load changes. Two flange joint type configurations are treated: a joint with identical pair of flanges and a joint with a cover plate. The analytical models are validated and verified by comparison to finite element results.

Bolted flange joints are widely used in the nuclear power plants and other industrial complexes. During their assembly, it is extremely difficult to achieve the target bolt preload and tightening uniformity due to elastic interaction and criss-cross talks. 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 and bolt load changes during tightening. The developed model can be used to optimize the initial bolt tightening to obtain a uniform final preload under minimum tightening passes. The approach is validated using finite element analysis (FEA) and experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joint.