Thermo Mechanical Coupling Analysis And Sealing Material's Performance Study Of Ultra-low Temperature Ball Valve

As the rapid development of China's petrochemical industry,cryogenic engineering and liquefied natural gas(LNG)industry,the demand of low temperature valves is more and more big,especially the cryogenic valves which working temperature are below-150 degree,and the domestic design and production requirements of cryogenic valve are increasingly high.The stem and the packing of cryogenic valve are easily freezing under the working condition,which will affects the opening and closing of valve,as well as its sealin g performance and service life,therefore,it's usually required to ensure the bottom temperature of the stuffing must at least reach 0 degree.At the design time,the structure of cryogenic valves generally use the long necked bonnet with a drip tray,the sealing ring on the packing seal and other key parts of the structure are using multiple sealing,and the sealing material selection is also preferred polymer materials with excellent low temperature properties.This paper aimed at the special requirement s of cryogenic valves,primarily combined the results of low temperature test of LNG ultra-low temperature ball valve,analyze ultra-low temperature ball valve with temperature finite element analysis method,and obtain the curve relationship between the temperature of valve stem,the root of the drip tray and the inner temperature of valve body.Then compare the curve with the experimental data to verify and analysis,so as to obtain a conclusion that the bottom temperature of stuffing box is higher when the drip tray is installed in a lower position.Regarding the LNG ultra-low temperature valve working condition,establish a simplified model of the upper part of the valve body,using the coupled thermal and structural analysis method,analyze the conditi on when low temperature and stress structure interact the model,as well as the deformation and displacement caused by the coupled stress.Then separately simulate the condition which only applied the structure stress or temperature stress,through the com paring of stress and deformation results,discovered that the effect of temperature stress on the ultra-low temperature ball valve is greater than the structural stress,and the two kinds of stress will cancel each other while coupling;the axial stress deformation is large,circumferential deformation is small relative to the gap between bonnet and stem,and some optimization suggestions for structural design are given accordingly.The selection of sealing material is concerned about the using reliabilit y of valves,so design several low temperature performance test of the new polymer materials which called polytrifluorochloroethylene(PCTFE),analyze its hardness,compression and resilience properties under different temperature,obtain that the compressibility of PCTFE decreases with the decrease of temperature,the elastic resilience changes little with the fall of temperature,and the sealing performance is relatively reliable at-110? and above,thus provides data support for the use of new material in ultra-low temperature valves.