Content area
Abstract
Structurally sound bolted joints often fail due to loss of tightness. This is because the clamping load is affected not only by the application of the internal fluid pressure but also by the amount of creep relaxation, thermal degradation and difference in expansion of the joint members. Most significant contributions over the years were put towards better structural integrity performance of the joint while no particular attention was paid to the complex behavior of the gasket. With working conditions becoming more and more severe due to the required increasing performance and efficiency demands, it is evident that bolted flanged joints require rigorous analysis for both structural integrity and leakage tightness.
This thesis presents a study of a new and accurate approach to the modeling and design of bolted flanged gasketed joints. The new proposed design model that our program "POLYFLG" is based on, encompasses most aspects of joint behavior in order to produce both structural integrity and efficient sealing performance within the defined limits of the method used. The method is based on the elastic interactions of all the flanged joint elements taking into account their flexibility and considers the change in joint element dimensions during operation produced by temperature induced effects.
The work includes a detailed review of the literature on the design and analysis of bolted flanged joints. Also included is the development of a simple analytical model which is based on an extension of the Taylor-Forge approach to which flange rotation, flexibility of both the gasket and the bolts, friction between the gasket and flange and, when applicable, the stiffness of the end closure are incorporated. These parameters have a strong influence on the gasket and bolt stresses and have partly enabled us to resolve some ambiguities and to better understand the complex mechanical behavior of bolted flanged joints.
In addition, the proposed model accounts for the short and the long term behavior by simulating the relaxation of the remaining load on the gasket after the application of the internal fluid pressure and temperature. The influence of the bolted joint stiffness on the relaxation of the gasket is clearly demonstrated. In general, the results obtained by the proposed model compare well with those obtained experimentally, at room temperature, on real bolted flanged joints. In some cases comparisons are made using finite element analyses.
Finally, an improved model capable of taking into account most of the parameters involved and guiding the designer towards a long term safe leak design have been developed. The proposed model has potential for becoming a design tool for leakage prediction.
