Research On Transient Sealing Design Method Of Large Caliber Flange At High Temperature

The study of the flange sealing is the key part of the joint for the flange and pipe. The large caliber flange at high temperature is prone to leaking out because of the increase of the caliber, the fluctuation of the temperature and the pressure, so research on transient condition of large caliber flange under high temperature becomes the current research focus in sealing field abroad, but no research work has been found at home. Therefore, the dissertation carry out the research on transient sealing design method of large caliber flange at high temperature systematically, established a percolation model of the nonmetallic porousmedia gasket, the large caliber flange was simulated at multi-condition using three-dimensional FEM, the major causes effecting the leakage of the flange were discussed deeper controlling the leakage, numerical experimentation for the sealing performance of the flange parameters was carried through based on the orthogonal design, brought forward the transient sealing design method of the flange based on the tightness. Main advances of the research in this thesis are summarized as follows:1. Percolation model of the nonmetallic porousmedia gasket and the leakage rate formula were established and derived considering the relationship between compress stress of gasket and porosity etc. Based on the leakage rate test of the spiral gasket, the leakage rate formula was regressed, which was used to predicate the leakage rate of the gasket and toke as the criterion.2. Considering the non-linear contact problem between the nut and flange, the gasket and the flange, as well as the non-linear of the performance of the gasket, a large caliber flange mechanical FEM model was set up and analyzed at preload condition. A three-dimensional heat transfer model was established at the same time, the stationary and transient temperature field and the thermal-construct coupling fields were simulated. The relationships between the stress of the gasket and the load of the bolt, the stress of the gasket and the temperature of the flange, the stress of the bolt and the preload were gotten, the relations among the stress, temperature and the time etc were also gotten at the transient temperature field. These rules were beneficial to the design of the flange and the on-line detection for the stress of the bolt.3. L27 (313) and L18 (37) orthogonal table were built, and the effect of the pressure, temperature, resilience modulus of the gasket and the preload of the bolt on the stress of the gasket were investigated using the orthogonal design and finite element analysis. The formula among the stress of the gasket, the operating temperature, pressure of the flange, resilience modulus of the gasket and the preload of the bolt was regressed. At the same time, the formula among the resilience modulus and the parameters of the graded manufacturing technique of the spiral gasket was regressed using the data from the experiment of the graded manufacturing technique of spiral wound gaskets, consequently the graded manufacturing technique could be used to control the performance of the spiral gasket to meet the needs of the practical situation.4. The transient sealing design method of the flange based on the tightness was put forward and programmed. This method preestimated the stress of the gasket under the condition of the fluctuation of the temperature and the pressure during the design of the flange, then diagnosed whether the leakage rate of the flange could satisfy the criterion using the leakage rate formula, otherwise it would change the preload of the bolt or adjust the resilience modulus of the gasket using the graded manufacturing technique of the spiral gasket unchanging the structure parameters of the flange to satisfy the tightness adjusting the leakage rate in a range and realize the flange sealing design under transient condition.