Comparison Between Different Calculation Methods for Determining Bolting-Up Torque Moments

The ASME BPVC, Section III, Appendix XI [1] regulates the flange calculation for class 2 and 3 components in Suisse nuclear power plants, and it is also used for class 1 flanges. The most common European Standard for the design of bolted flanged joints is EN 1591-1 [2], the required gasket characteristics for this calculation procedure are defined in EN 13555 [3]. These characteristics can be determined experimentally and they are not only used in EN 1591-1 but also in more realistic finite-element calculations. Finite element calculations are carried out for a certain number of combinations of flange and gasket materials as well as bolt types in order to prove compliance with the integrity and tightness of the connections in the assembly and subsequent operational states, taking into account the tightening torques. A total of almost 400 different combinations of flange, bolt and gasket geometries and materials were examined. The focus is laid on flange types fabricated according to European standards which are generally thinner — looking at the wall thickness or flange ring in the same pressure range — than in the ASME world. In this paper the bolting-up torque moments determined with the European standard EN 1591-1 for the flange connections, are assessed with twice elastic slope method, limit load and elastic-plastic stress analysis according to ASME BPVC, Section VIII, Div. 2. [4] Proof of acceptability of the nonlinear finite element-calculations are conducted according to ASME standard procedures like ASME SECTION III, Appendices EE and FF for the level D.