Tightness Evaluation Of High-temperature Pipe Flange Connection

Tightness of high-temperature pipe flange connection is an important index of high-temperature equipment integrity.Therefore,it has important engineering significance to study the tightness of high-temperature pipe flange connection system.According to the traditional equivalent pressure method and equivalent axial force method can not accurately characterize the rules of gasket stress distribution under the bending moment,so a modified equivalent axial force method that could show the uniform distribution of gasket was proposed,and the deformation coordination equations of flange joint with external bending moment and creep was constructed.The results showed that the modified equivalent axial force method could be used to characterize the nonlinear distribution of the gasket stress under the external bending moment.Under the action of creep,the left side of the gasket was pulled,the stress decreased gradually with time,and the right side of the gasket was compressed,the stress increased gradually with time.After 2000h,when the external bending moment was 1×10~4N·m,the difference between the tension side and the compression side of the gasket stress was 3.6656MPa.when the external bending moment was 6×10~4N·m,the difference between the tension side and the compression side of the gasket stress was 21.9937MPa;Based on the design method of minimum bolt load in PVRC,the evaluation method of minimum gasket according the level of tightness was given,and combining with leakage rate to modify the gasket coefficient m,three kinds of gasket coefficient calculation method that related to tightness level,temperature,internal pressure,gasket width and gasket diameter was put forward.Taking the flexible graphite composite gasket of DN300,PN10.0 for example.at room temperature,when the tightness level was?,corresponding gasket coefficient m were 6.791,10.48,12.733;at 400?,when the tightness level was?,corresponding gasket coefficient m were2.154?3.324?4.039.The results showed that the modified gasket coefficient could be used to evaluate the tightness of flange joint preferably under working conditions.The creep fatigue testing machine was used to analyze the gasket compression resilience performance under the different influencing factor of temperature,loading rate and peak load holding mode,the gasket compression resilience curves under different conditions were received respectively.The test results showed that the increase of temperature and loading rate would reduce the performance of gasket compression resilience.At room temperature,the compression ratio was 96.76%;after unloading,the rebound rate was 0.716%.At 200?,the compression ratio of the gasket was about 81.076%,and the rebound rate was about 9.135%after unloading.Particularly,when the loading rate increased from 0.05MPa/s to 0.1MPa/s,the change of compression rebound curve was not obvious.When the loading rate was less than0.1MPa/s,the characteristics of the loading rate irrelevance that the relationship of gasket compression resilience performance was shown.And in the 1min peak loading process,gasket compressive strain increased with temperature increased significantly,the gasket maximum strain under 200?was 5.46 times of the gasket maximum strain under room temperature.Finally,a set of test equipment and scheme for simulating the leakage of pipeline flange connection under the actual working condition was designed.The leak medium of this test device could not affect the bolts and the gasket normal stress,the results was more actual.