Amount of cryogenic valve repair, valve repair is relatively small, but in cryogenic valve repair, the low temperature cut-off valve door repair is a relatively large amount of cryogenic ball valve repair or maximum Oulei Si valve repair; Jiangyin that: Only by fully understanding the structural design of the low temperature cut-off valve in order to better low temperature cut-off valve repair. Ultra-low temperature cut-off valve repair, cut-off device is used in low-temperature conditions, general conditions temperature below -100 ℃ temperature industrial occupies an important position in the industrial field, natural gas, for example, in order to make natural gas more convenient transportation, The general industrial cooling and compression method gasification gas converted to liquefied natural gas (LNG), the boiling point is -162 ° C under normal atmospheric pressure, volume, after vaporization of the liquid when the 600 times [1]. Ultra-low temperature cut-off valve as a main valve cryogenic industrial important cut-off device, developed for to -196 ℃ ultra-low temperature conditions, a large number of research trials, its sealing structure design and research of major significance .704 Institute ultra-low temperature valve can work in this temperature environment prototype (Fig. 1).
Material requirements of ultra-low temperature cut-off valve
Material requirements of ultra-low temperature cut-off valve
Conditions applied at room temperature, the valve, the wide range of material selection. Conditions of the use of ultra-low temperature cut-off valve below -100 ℃, the more stringent requirements on the materials. At the working temperature, the material should not produce low-temperature brittle fracture, the organizational structure of the material should be stable, and to prevent the phase change material caused by the volume change; welded structure, the material better welding performance, at low temperatures the weld has higher reliability; valve in the low-temperature conditions frequent opening and closing parts of the valve stem, seat should avoid jamming bite scratches phenomenon. Based on the above requirements, the recommended use of materials of low temperature cut-off valve main parts as shown in Table 1 [2].
2 ultra-low temperature cut-off valve the main seal structure design
Ultra-low temperature cut-off valves with the structure of the valves and valve seat contact with cone seal, seal pair of metal-on-metal hard sealed form, seat design on the valve body and the valve is designed to form an integrated structure, as shown in Figure 2. In order to ensure the reliable sealing of the valve, the valve and valve body sealing surface the spray welding Carbide. Low temperature test and coated mechanical testing to prove the spraying increased hardness, good wear resistance of low-temperature environment, and promote reliable sealing of the valve in the low-temperature environment. Access to data and experimental applications, using plasma spray technology on the valve sealing surface the spray welding StelliteNo6 alloy, the valve sealing surface the spray welding StelliteNo12 alloy, thickness ≥ 1mm. After Spray Process the attached StelliteNo12 alloy valve sealing surface hardness than attached StelliteNo6 alloy valve body sealing surface hardness is conducive to the cut-off valve seal.
Ultra-low temperature cut-off valve stem drive the valve through a straight line up and down movement of the valve opening and closing. Increase in the design of the valve body, the sports-oriented features of the valve, the valve body design of the cylindrical guide wall, the smooth movement of the valve flap valves open and close and reliable. Meanwhile, in the production process of the valve, since the seal face and valve sealing surface of the valve flap are spray welding Stellite alloy, greatly improved in hardness, a certain difficulty in the processing and grinding of the sealing surface, while the main sealing surface must be precise grinding tie to an effective seal. Guide wall design allows the valve flap and valve sealing surface in contact with a more uniform conducive to achieve reliable sealing process of the cut-off valve.
The main sealing structure according to the ultra-low temperature cut-off valve, using ANSYS software its sealing performance simulation. Ultra-low temperature cut-off valve in the low temperature state, the sealing pressure ratio obtained by finite element analysis, to determine the performance of the valve sealing.
Geometric modeling in order to establish the model is easy to finite element analysis, the actual model does not affect the analysis of the structure and properties of some part of some simplification, such as screw holes, bolts, gaskets. Impact to prevent the pipeline ends of constraint to the valve body itself, the import and export external piping each lengthened 0.3m create three-dimensional model is shown in Figure 3.
Finite element modeling and simulation content by definition valve material performance parameters, boundary conditions, load conditions, simulation, sealing surface pressure distribution in Figure 4 shows
Obtained by the simulation results, the ultra-low temperature shut-off valve in the low temperature condition, and its sealing surface than the pressure seal between the pressure ratio and Xu than the pressure within the scope of the sealing structure of the valve can achieve an effective seal.
3 ultra-low temperature cut-off valve outside the sealed structural design
The ultra-low temperature cut-off valve outer sealing in flange sealing and long-necked bonnet top seal (the seal). The outer seal structure shown in Figure 5 and Figure 6.
Ultra-low temperature cut-off valve flange at the stainless steel spiral wound gasket sealing. Must be in accordance with its sealing pressure ratio to calculate the torque applied to the flange bolts, through the preload force to achieve a reliable seal. The bolts at the installation of the dish spring preload and displacement compensation.
The threaded connection tightening torque with the formal determination of a torque wrench tightening torque required torque [3]:
T = K? F0? D (Nm) (1), F0 the single bolt tensile stress (N); K for the screw tightening torque coefficient, taking 0.2; d for the thread, in diameter. Thread specifications for the M16, the number six, for example calculation of available torque T = 47Nm. Calculated by the theory, in the valve assembly process, using a torque wrench 47Nm torque is applied to the flange bolts.
Testing of the valves in the normothermic and hypothermic, flange at a good seal. However, ultra-low temperature cut-off valve after dismantling the spiral wound gasket may repeatedly squeezed by flange deformation, loss of sealing effect. Flange gasket should be equipped with spare parts for dismantling the installation of replacement wearing parts. The ultra-low temperature cut-off the upper part of the valve stem packing seal + stem cone seal double seal structure. The structure can be realized in a completely open position of the valve, metal hard seal and soft packing seal double effect. Valve opening and closing process and close the state where sealed by packing alone.
At the stem seal designed as a tapered surface (designed here as 45 °, can also be designed according to the actual situation for the other angles) and, after grinding, by an external driving force so that the tapered surface of the stem is pressed against the long-necked valve cover interior the same angle on the cone, sealing effect.
When the ultra-low-temperature cut-off valve on the seal by the filler alone to achieve through the calculation, packing gland preload applied to the filler, and be installed on the bolt dish spring preload force and displacement compensation overcome changes due to the high and low temperature filler produced by micro-expansion and contraction, and seal preload change.
Packing gland bolts to connect the tightening torque reference to Equation 1. Example, was here two M12 bolts torque T = 28Nm. Assembly, use a torque wrench to 28Nm torque applied to the bolts here.
4 Conclusion
In summary, the low temperature cut-off the seal valve repair technology in the design is feasible, the processing can be achieved. 704 Institute has developed surplus low temperature cut-off valve prototype units, and the prototype was done at room temperature and ultra-low temperature test. On the basis of the current results, continue the serialization of ultra-low temperature valve technology research has far-reaching significance for the development and exploration of low-temperature industrial and ultra-low temperature areas, only familiar with the various types of valve repair structural design to better valve repair.
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