Effect Of Creep On The Sealing Of Metal To Metal Contact Bolted Flange Joints

With the deterioration of the environment and increasingly tense energy, energy conservation and environmental protection have become a consensus. On this basis, the transformation of insulation and energy conservation for large-scale flange joints in petrochemical enterprises has gradually obtained attention. In recent years, metal-to-metal contact (MMC) flange joints have been gradually promoted to the petroleum, chemical and other industries and occasions with severe working conditions due to its excellent sealing performance, in order to replace spiral wound gaskets. However, there are few researches of the metal-to-metal contact bolted flange joints. Currently, there are not formally promulgated design calculation standards, and there is also lack of research about sealing performance under high-temperature conditions. This paper carries out experimental research and simulation analysis of the metal-to-metal contact bolted flange joints at elevated temperature, in order to ensure its security application in engineering. The main content and results of this paper are as follows:(1) Design a high-temperature test equipment of DN600 CLASS300 metal-to-metal contact bolted flange joints, and obtained the temperature field of joints below 500℃, flange rotation under preloading and high-temperature steady-state conditions, and the leakage rate of the joints was also measured using the pressure drop method;(2) Analysis the temperature field of flange joints before and after insulation, compared with the experiment. The results show that, the insulation operation improves the temperature of the entire joint, so that the temperature of every component of the joint tends to be the uniform and close to the inner-wall temperature of flange, and the finite element analysis results are close to the test results;(3) Analysis the gasket stress and load allocation under preloading, pressurization and high-temperature steady-state conditions. The research finds that, after establishment of MMC, an excessive bolt load is not conducive to sealing; pressurization almost does not have an impact on the sealing performance; insulation can reduce the heat stress of flange joints; temperature has a greater impact on the gasket stress of MMC joints. However, MMC still exists, with reliable sealing performance, which is consistent with "zero" leakage of joints tested under high-temperature steady-state conditions;(4) Analysis the creep relaxation rules of MMC flange joints. At elevated temperature, with the relaxation of bolt load, force on MMC area is gradually reduced until separation from MMC, bringing threats to the reliability of flange joints. Hot tightening is recommended during its five-year service period;(5) Under creep condition, based on strength and maximum gasket stress, it is recommended that the initial installation stress of bolts is 30% to 40% of the bolt yield strength at room temperature.