Inelastic Analysis of Dissimilar Material Flanges With Metal Ring Gaskets at Elevated Temperature

The dissimilar material flange connections are often adopted to connect the austenite stainless steel pipes to the low alloy steel pressure vessels operated at an elevated temperature. The behavior of this flange connection is very complicated because of the non-uniform temperature distribution and the thermal expansion difference of dissimilar materials. The application of the metal ring gasket makes the behavior more complicated. An elastic plastic finite element analysis is one of the adequate ways to investigate the behavior of the following dissimilar material flanges with the metal ring gasket under the high pressure and elevated temperature operation. (1) Pipe flange: standard configuration, austenite stainless steel, (2) Nozzle flange: forged thick nozzle neck, low alloy steel covered with stainless steel overlay. The material of ring gasket is also an austenite stainless steel. This ring gasket contacts to and slips on the ring groove surfaces of flanges. The axi-symmetric analyses were made considering the sequence of initial bolting, internal pressure and non-uniform temperature distribution. The elastic plastic properties and temperature dependency of the materials were considered. From these analyses, the effects of the non-uniform temperature distribution and the thermal expansion difference of dissimilar material flanges on the contact pressure of the ring gaskets were made clear. The effect of flange size (14”–36”) was also investigated.