Study On High Temperature Sealing Performance Of Flanged Bolt Joint Of Gate Valve

Sufficient and stable bolt load is the key to realize effective sealing of flange bolt joint.The research on the flange bolts in the existing industrial gate valves couldn't fully understand the sealing leakage problems such as the shortage of bolt load,the failure of the gasket and the excessive deflection of the flange,and so on.Facing such problems,the corresponding experimental apparatus was set up,the change rules on the normal temperature bolt pre-tightening and booster heating process were studied.On this basis,the effect of different pressure and thermal tightening on the original sealing performance were analyzed by combining the finite element method.In this paper,the mechanical behavior change of the joints under long time was discussed and the prediction system was established.The main work of this paper was followed:?1?A normal temperature pretightening test device for business with ten bolt flange joint of 4Z6AA22P?S?gate valve was set up.The bolt load distribution under the preloading standard of ASME PCC-1-2013 and JIS B 2251 was compared and analyzed.The experimental results showed that the average load that was obtained by the ASME PCC-1-2013 and JIS B2251 pretightening standard was near the expected target load about 70%.The JIS B 2251 bolt pre tightening standard achieved better load and evenness than the actual load.The bolts needn't be numbered when loading,but the loading process was laborious.Based on the elastic interaction mechanism,the four parameter method was put forward to optimize the loading mode.The experimental results showed that the four parameter method could effectively reduce the elastic interaction in the loading process,and obtain the actual bolt load close to the target load with less full scale and uniformity,but the calculation process was more complex and needed to be predefined.?2?A measuring device for the load change of the high temperature gate valve bolt was set up.The full model external heating method was used,and the change law of the bolt load on the first and two times of the temperature process was experimentally studied.The results showed that when the temperature rised to 723 K,the average load of the bolt decreased by more than 40%compared with the initial pretightening state.Due to the influence of the compression and resilience of the gasket and the thermal expansion coefficient of each component,the springback phenomenon of the bolt load would appear during the rising and falling process.The pressure source was introduced,and then the effect of pressure on bolt in temperature field was analyzed.The results showed that the tensile stress at the end of the valve body caused by the internal stamping reduced the deformation deflection caused by the heat stress of the flange,and the pressure intervention could inhibit the drop of the bolt load.But at the same time,the study showed that the temperature was still a dominant role in the bolt load change during this condition whose pressure was 3 MPa and temperature was 723 K.?3?Based on the physical and geometrical structure and heat transfer theory of gate valve,a coupled thermo structural finite element model of high temperature gate valve was established.The variation of bolt load,gasket stress and flange deflection under the combined action of 0⁴ MPa pressure and 288⁸73 K temperature was simulated.The results showed that the trend of bolt load varying with temperature was affected by the pressure.Under different pressures,the bolt load decreased rapidly.The stress change of the gasket was basically synchronized with the change of the bolt load,and the stress extending ring of the gasket increased gradually from inside to outside,and the minimum stress in the gasket could meet the sealing needs in the limit state.The maximum deflection of the flange was transferred from the upper side of the middle flange to the lower side during the heating process,and then increased continuously.?4?Based on the temperature drop phenomenon of bolt load,a simulation analysis of the hot tightening operation of each bolt at 673 K temperature was carried out.The change of bolt load under different hot load and loading mode was compared.The results showed that under the same preloading,the bolt load was close to each other by two ways,but the uneven load caused by cross loading increased several times.In the process of increasing the preload from0.8F₀ to 1.2F₀,the load capacity was increased but not obvious.It was pointed out that in a round of heat tightening,a better sealing effect could be obtained by using the heat tight force near the target load and the sequential loading method.?5?Based on thermo structure coupled finite element model,a prediction system for sealing performance of flanges of gate valves during long time operation was established.The creep changes of each component were analyzed in detail at 10000 h running time with 2 MPa working pressure and 823 K working temperature.The results showed that the bolt load decreased exponentially in the first 2000 h before operation.At this time,leakage was mainly caused by excessive load drop,resulting in too low stress of gaskets.During subsequent long time operation,there would be more and more concentrated stress areas on the gaskets.The valve body itself would have the reformer stress due to the thermal stress.Therefore,in the design and operation stage,the extra attention about performance of the material and bolted gasket of the valve body should be paid.