Sealing Performance Of Bolted Flange System At High Temperature

The research on the temperature distribution and sealing performance of the bolt-flange-gasket system at high temperature is of great importance to prevent high temperature failure of the static sealing system. In this paper, bolt preloading scheme at room temperature was researched through the experiment method, which aimed at getting uniform bolt load. Based on this, the temperature and stress of bolted flange system at high temperature under the steady state and transient state were analyzed through the numerical simulation method, and the changement of the sealing performance in different high temperature conditions was discussed, which were used for evaluating the sealing performance.The main work and conclusions are as follows:(1) The finite element model of structural analysis which is also the FE model of thermal-structural coupling field analysis was established. Three kinds of heat transfer model were established according to heat transfer theory, and based on it the FE model of thermal analysis was established. The method of importing the temperature field to structural analysis was discussed in the thermal-structural coupling field analysis.(2) Using existing experiment device, the functioning law of making level sequencely by target load value in bolt tightening was studied, and four-pass loading method in the tightening step was optimized. Based on this, the improved bolt preloading scheme was proposed, and then compared with the experimental result under ASME PCC-1and HPIS Z103TR tightening method. At last, bolt preloading scheme in engineering practice was given. The study reveals that:In the tightening step, the first pass is tightened by cross pattern, and the followed three passes are tightened by sequence pattern. In the making level step, two passes making level sequencely by target load value can make the dispersion degree of bolt load reduced. The bolt can produce relaxation in the short term, and the overall level of bolt load will be improved by exerting the post-tightening step, which is favorable for the sealing.(3) The steady state temperature field and coupling field of bolted flange system at high temperature were analyzed by numerical simulation. Based on this, the stress distribution of gasket and bolt at different temperatures and the stress variation law when the internal pressure fluctuates were analyzed, and the sealing performance of system at high temperature was evaluated. The study reveals that:After the temperature rises, the gasket outside stress decreases while the inside stress increases, the average stress decreases and the bolt stress increases. The higher the temperature of medium is, the smaller the gasket stress is and the bigger the stress difference between inside and outside is. After the internal pressure fluctuates, the gasket stress decreases. The bigger the pressure fluctuates, the more the gasket stress decreases and the bigger the stress difference between inside and outside.(4) The transient state temperature field and coupling field of bolted flange system at high temperature were analyzed by numerical simulation. On the premise that the internal pressure was constant, the temperature and stress variation of gasket and bolt were studied in the process of equipment initial temperature rising, temperature fluctuation at the working state and equipment final temperature falling. And the stress variation of gasket and bolt was studied when the temperature and internal pressure fluctuated at the same time. The study reveals that:When the internal pressure is constant, the speed of temperature rising should not be quick in the process of equipment initial temperature rising, the range of temperature falling should not be big in the process of temperature fluctuation at the working state, and it is more dangerous in the process of equipment final temperature falling. When the temperature and internal pressure fluctuate at the same time, the smallest gasket stress appears at the stage of the temperature and internal pressure falling at the same time, and the bigger the range is, the smaller the gasket stress is.