Limits of Allowable Static and Cyclic Loads on Lens Ring Gaskets

Abstract

Due to their relative simple handling and the high reliability, lens ring gaskets are widely used in high pressure connections. In addition, they are able to withstand large external forces without being damaged but at the same time they do not lose leak tightness even with very small contact forces. This ability to withstand high loads allows a lens ring gasket to be reused several times with minimal polishing after disassembling the flange connection. However, this reusability has its end when the lens ring gasket is damaged or destroyed by static or cyclic overload. Static overload is mainly caused by too high bolt tightening force and leads to large scale plastic deformation. This damage can be easily avoided by choosing the correct bolt preload and proper flange alignment. A greater difficulty is the damage prediction by cyclic overload. This is caused by pressure fluctuations, excitations in the range of natural frequencies or other external cyclic loads. The effects of these mentioned loads on the service life of the lens ring gasket additionally depend on factors such as the stiffness of the individual components of the flange connection, the initial bolt preload or the materials used. In the present work a method is presented which is able to predict the load limits of lens ring gaskets under static and cyclic loading. This method allows the consideration of different geometric influences of the individual components, of different materials and bolt preloads. From the static and cyclic forces on the flange connection, local stresses in the lens ring are calculated. This enables making a statement regarding plastic deformation due to bolt load and fatigue failure due to cyclic loads.