The effect of bolt spacing on the tightness behavior of bolted flange joints

摘要

Bolted flange joints form a part of pressure vessels and piping components, and are used extensively in the chemical, petrochemical and nuclear power industries. They are simple structures and offer the possibility of disassembly, making them attractive for connecting pressurized equipment and piping. In addition of being prone to leakage, they often require maintenance while in operation, in which case the bolts are either retightened, as in hot torquing, or untightened for replacement. Although such maintenance work prevents costly shutdowns, it can nevertheless expose the operator to a potential risk because altering the bolt load can produce a gasket load unbalance, which results in a local gasket contact stress drop below a critical value, causing a major leak, and putting the operator’s life at risk.ududThis proposal addresses flange deflection variation as it investigates the flange contact stress level unbalance around the flange when the bolts are subjected to a load alteration during operation. This study may serve to help limit the degree of load increase in hot torquing or the maximum number of bolts to be replaced at a time, and to identify the flanges whose bolts cannot be replaced while they are in operation.ududThe objective of this study is to determine a theoretical approach for identifying and analyzing the effects of initial bolt-up and pressurization on the bolted flange joints, in order to obtain a solution for bolt spacing calculation, according to different gasket contact stress variation levels. Our research breaks down into three parts. The first part, an analytical method based on the theory of circular beams resting on a linear elastic foundation, is developed to predict the circumferential distribution of gasket contact stresses. Finite element model of symmetry bolted flange joints is created for use in evaluating the analysis. Then, as a second step of this research, an approach based on the theory of a ring on a non-linear elastic foundation behavior is applied in order to get more accurate results than linear model solution. This part is applied to non-linear solution and then validated by finite element analysis. In the third part, a linear regression model is developed to propose bolt spacing calculation procedures for bolted flange joint connections. In industrial practice, this work should help in designing, maintaining and operating technical pressure vessels and piping systems.