Deformation behaviour of large, high-pressure vessel flanges. Chapter 1

The analysis of the deformation behaviour of large, high-pressure vessel flanges can be performed by approximating the flange design using basic shell-, rigid ring- and beam-elements. Typically, the narrow flange faces cause the gasket reaction moments to be relatively large compared with the bolting moment, thereby requiring an exact knowledge of the radii of application of these reactions. This can only be included in the former computational procedure in an approximate manner. Furthermore, the plastic deformation of the gasket faces may influence the accuracy of a linear elastic analysis, whereas the rigid ring concept may result in inaccuracies with regard to the overall elastic behaviour of the flange rings. The aim of the present chapter is to supply information on the above subjects. Therefore, two particularly narrow flange geometries (typical of PWR flanges) were analysed by both elastic and elasto-plastic finite element models, computational results being compared with results obtained from the computational procedure mentioned above and with experimental results. Experimental data on local gasket face deformation were obtained by a specially developed beam apparatus, with the leak detection channel of the flange (of a full-scale PWR-vessel) serving as a beam hole. Flange rotations were determined from strain gauges on four full-size PWR-pressure vessels. Additional strain gauges were used on the bolts for the determination of the bolt stresses. Other subjects treated in the chapter are the prediction of membrane and bending stresses in the bolts, the influence of the friction between upper and lower flanges, and some particular aspects of the computational procedures. (author)