Finite Element Analysis on Bolted Flange Connection Subjected to Bending Moment and Thermal Loads

Abstract

Gasketed flange connections should be designed taking into consideration the actual behavior of the connections under their operating conditions. However, such actual behaviors as the bolt load change, the gasket load change and the flange rotation are not considered in the current design calculation method due to the difficulty to solve a statically indeterminate problem among three bodies, flanges, bolts and gasket. In this paper, the authors perform finite element analyses on a 4 inch bolted flange connection with a spiral wound gasket inserted subjected to the bending moment or the thermal load in addition to the internal pressure. It is taken into consideration the nonlinearity shown in the loading-unloading curve of the gasket. For the bending moments, the gasket contact stress distribution due to the bending moment after pressurizing is evaluated by using a 3-dimensional FE model. The calculated gasket contact stress is compared with the one obtained from the extended load factor method to calculate the behavior of the flange connection subjected to bending moments. The authors propose the extension of the load factor method incorporating with the concept of the conventional equivalent pressure representing the bending moment. For the thermal load, an axisymmetric FE model is utilized to evaluate the changes in the flexibility and the thermal expansions of the flange connection at the elevated temperature. The authors also extend the load factor method to incorporate with the change of the flexibility of the flange connection and the thermal expansion depending on the change of temperature. The results obtained from the extended load factor method are cross-checked with those from the finite element analysis.