A variable usually overlooked in a gasketed connection is the bolting system. Proper design and selection of the bolting system can provide an extension of gasket life by orders of magnitude. One of the most important factors is the bolting system's overall spring constant. Spring constant affects not only torque loss, but the gaskets dynamic loading. A high spring constant system will have a higher per cent torque loss than a low spring constant system. Lowering the spring constant reduces the so-called pounding of flanges causing the gasket to crush and fail. It allows the gasket to absorb the bolts cyclic loading by transferring it to a larger gasket area. Spring constant is lowered by reducing bolt diameter, increasing bolt length and, if possible, reducing the number of bolts.
When flanges are made of dissimilar metals, bolting plays a most important part in obtaining and maintaining a satisfactory seal. The fasteners as well as the gasket must be able to compensate for difference in expansion of the different flange materials. The old, never forgotten rule -- if leakage at a flange is observed, use larger bolts and higher torque -- must be repealed.