Akli Nechache

An Analytical Solution for Evaluating Gasket Stress Change in Bolted Flange Connections Subjected to High Temperature Loading

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.

The Determination of Load Changes in Bolted Gasketed Joints Subjected to Elevated Temperature

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 a temperature change 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.Copyright

Thermally induced deflections in bolted flanged connections

Pressure vessel joints operating at high temperature are often very difficult to seal. The existing flange design methods do not address thermal effects other than the variation of flange material mechanical properties with temperature. It is possible to include the effects of temperature loading in joint analysis, however, presently very few guidelines exist for this type of analysis. This paper outlines the theoretical analysis used for the determination of the steady state operating temperature and deflections in bolted flange joints. It details the theoretical equations necessary to predict the temperature profiles and thermal expansion difference between the joint components necessary for the evaluation of the load redistribution for the two cases of a flange pair and a flange with a cover plate. The results from the theoretical models are verified by comparison to finite element results.

Creep Modeling in Bolted Flange Joints

Bolted flanged connections are used extensively in the petrochemical and nuclear industries. Under high temperatures, their leakage tightness behavior is compromised due to the loss of load as a result of creep of not only the gasket material but also the bolt and the flange materials. The relaxation of the bolt load and the corresponding loss of the gasket contact stress are not easy to assess analytically and consequently there is no established design calculation procedure. The objective of this paper is to present an analytical method that is part of the SuperFlange program [1] and is capable of predicting the load relaxation in a bolted joint when subjected to flange, bolt and gasket creep. The proposed method is validated by comparison with 3D FE models of different size flanges. In some cases, the relaxation caused by the flange and bolt materials is shown to be significant.Copyright

The Redistribution of Load in Bolted Gasketed Joints Subjected to Steady State Thermal Loading

Pressure vessel joints operating at high temperature are often very difficult to seal. The existing flange design methods do not address thermal effects other than the variation of flange material mechanical properties with temperature. It is possible to include the effects of temperature loading in joint analysis, however, presently very few guidelines exist for this type of analysis. This paper outlines the theoretical analysis used for the determination of the steady state operating temperature and the induced loads in flange joints. It details the theoretical equations necessary to predict the temperature and the redistribution of load due to the thermal expansion of the joint components for the case of a pair flange and the case of a flange with a blind-cover. The results from the theoretical models are verified by comparison to finite element results.Copyright

On the Use of Belleville Washers to Reduce Relaxation in Bolted Flange Joints

Bolted flange joints are prone to leakage when exposed to high temperature. In most cases this is due to relaxation that takes place as a result of material creep. One way to solve this problem is to use Belleville spring washers or longer bolt with spacers. However, there is practically no reliable analytical model that can evaluate the exact number of washers or length of the bolts required to reduce relaxation to a target minimum level. This paper describes an analytical model based on the flexibility and displacement interactions of the joint different elements including the axial rigidity of the flange and bolts, used to evaluate relaxation. The developed analytical flange model can accommodate either Belleville spring washers or longer bolts with spacer tubes to reduce the bolt load loss to a maximum target value. This model is validated by comparison with the more accurate FEA findings. Calculation examples on a bolted flanged joint are presented to illustrate the suggested analytical calculation procedure.Copyright

The Effect of Cylinder and Hub Creep on the Load Relaxation in Bolted Flanged Joints

The leakage tightness behavior of bolted flange joints is compromised due to the high temperature effects and, in particular, when creep of the materials of the different components of the bolted flanged joint takes place. The relaxation of bolted flanged joints is often estimated from the creep of the gasket and the bolts. The creep behavior of the flange ring, the hub, and the cylinder is often neglected. Apart from an acknowledgement of relaxation due to the creep, the designer has no specific tools to accurately assess this effect on the bolt load relaxation. The objective of this paper is to present an analytical approach capable of predicting the bolt load relaxation due to the creep of the flange ring, hub, and cylinder. The proposed approach is compared to the 3D finite element models of different size flanges. An emphasis will be put toward the importance of including creep of the hub and cylinder in high temperature flange designs.

Creep effect of attached structures on bolted flanged joint relaxation

The leakage tightness behavior of bolted flange joints is compromised due to high temperature effects and in particular when creep of the materials of the different components of the bolted flanged joint take place. The relaxation of bolted flanged joints is often estimated from the creep of the gasket and the bolts. The creep behavior of the flange ring and the attached structures such as the shell and the hub is often neglected. Apart from an acknowledgement of relaxation due to creep, the designer has no specific tools to accurately assess this effect on the bolt load relaxation. The objective of this paper is to present an analytical approach capable of predicting the bolt load relaxation due to creep of the attached structures. The proposed approach is validated by comparison with 3D FE models of different size flanges. An emphasis will be put towards the importance of including creep of the attached structures in high temperature flange designs.Copyright

Analytical modeling of a bolted flange joint subjected to creep relaxation

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.Copyright