Study On The Tightness Of Flange Connections Based On Nonlinear Gasket Constitutive

The study of flange connection compactness lineThe research on tightness of flange connections is the key to study the integrityof pressure vessels and pipes.Gaskets are important sealing elements,whose performance can directly affect the tightness of flange connections.Therefore,it is of great significance to study the tightness of the flange connection based on the nonlinear gasket.Considering the nonlinear compression resilience performance of gasket,the distribution characteristics of gasket compression force and flange deflection angle under the action of nonlinear bolt preload are studied,and discussed the tightness of the flange connection.The corresponding relationship between bolt preload and working pressure is established,and the corresponding relationship between bolt preload and the gasket stress is established,can find a bolt safe sealing range,[max{_bS~A,_bS~B},_bS~C],and when the operating conditions are changed,the effective sealing range of the bolt preload will also change.The results showed that the nonlinear compression resilience performance of the gasket affects the tightness of the flange connection.Researching on the creep law of flange connection under high temperature based on the flange deformation theory,and the creep equation of each element in the flange connection is derived theoretically.Circulating the gasket creep cycle and the creep law of the bolt force,the gasket force,the gasket compression and the gasket creep displacement are discussed.The minimum compression stress of the gasket is 44.8869MPa when the creep rate tends to be stable,which is greater than that of the minimum gasket pressure stress 4.05MPa that meets the gasket seal under the operation condition.Therefore,the gasket sealing performance of the flange connection system is good under the operating condition.Due to the bolt will cause the loss of the pretightening force after the heat expansion,so it is necessary to apply hot tightening operation on the bolt,and calculate the creep cycle of the flange connection again.Then compare the creep results with the first creep results,it is known that the hot tightening operation can compensate for the loss of bolt stress and gasket stress.In this paper,the concept of leakage rate is introduced.Based on the PVRC design method and the ASME standard,the concrete flange tightness evaluation method is proposed.The leakage rate of flange connections under different working conditions can be calculated from the basic sealing characteristic equation of gaskets,which can be used to determine whether the system meets the specified tightness.In addition,the minimum gasket stress under different working pressure to meet the requirements of tightness grade is different.Taking the flexible graphite metal composite gasket as an example,taking the different working pressure at 1.35MPa,3.5MPa,5.5MPa and 6.3MPa at room temperature,the corresponding minimum gasket stress is 3.571MPa,5.668MPa,6.730MPa and7.374MPa,respectively.By the deformation coordination equation,the calculated residual gasket compression stress and minimum gasket stress were compared,it can be determined whether the flange connection meet the tightness requirements under the specified conditions.