INELASTIC ANALYSIS OF SEALING CHARACTERISTICS OF FLANGES WITH METAL RING JOINT GASKET AT ELEVATED TEMPERATURE

摘要

In a previous paper presented in 2005 ASME PVP Conference, the authors investigated the elastic plastic behavior of dissimilar material flanges with a metal ring joint gasket operated at elevated temperature using FEA. Case studies were performed to study the effects of load path, material combination and flange size on the contact pressure and the plastic strain distribution in the ring joint gasket. In that paper, the authors concluded that the load path has a large impact on both, the contact pressure and the plastic strain, and, on the other hand, the material combination of the flanges and their size have small effects. In this paper, the authors present further FEA-based investigation on this mechanism. The first issue is the effects of meteorological changes, such as wind velocity, ambient temperature and rain, as is often the case with real energy and process plants. These meteorological changes result in the temperature change of bolts and flanges. The bolt temperature change causes different thermal expansion in the ring joint gasket and the bolts. This may affect the sealing performance. In this paper, the wind velocities were changed to investigate meteorological changes as a typical such change. The second issue is the behavior of the metal ring joint gasket after the second operation cycle. The metal ring joint gaskets are usually replaced after the first operation cycle, I.e., from start up to shut down. However, it is said that all ring joint gaskets are not replaced. In the previous paper, the behavior of the ring joint gasket during the first operation cycle was investigated. Increase of plastic strain in the sequential operation cycles is an important issue in terms of sealing performance. Therefore the behavior of the ring joint gasket in the second operation cycle was investigated. Finally the sealing mechanism and characteristics of this dissimilar material flanges under elevated temperature operation cycles were made clear.