The valve suitable for medium temperature -40℃～ -196℃ is called cryogenic valve. Cryogenic valves include cryogenic ball valves, cryogenic gate valves, cryogenic stop valves, cryogenic safety valves, cryogenic check valves, cryogenic butterfly valves, cryogenic needle valves, cryogenic throttle valves, cryogenic pressure reducing valves, etc., mainly used for ethylene, liquefied natural gas installations, and natural gas LPG LNG storage tanks, receiving bases and satellite stations, air separation equipment, petrochemical tail gas separation equipment, liquid oxygen, liquid nitrogen, liquid argon, carbon dioxide cryogenic storage tanks and tank trucks, pressure swing adsorption oxygen generation devices. The output liquid cryogenic medium, such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc., is not only flammable and explosive, but also vaporizes when the temperature rises, and the volume expands hundreds of times when it is vaporized. The application of cryogenic valves controls the temperature and prevents hidden dangers such as explosion and leakage.
Typical cryogenic valve structure: commonly used cryogenic valves include cryogenic gate valves, cryogenic globe valves, cryogenic check valves, cryogenic ball valves, cryogenic butterfly valves, etc. The middle cavity of the cryogenic gate valve and the cryogenic ball valve is provided with a "pressure relief hole" between the gate and the ball. All cryogenic valves are one-way sealed, and are cast on the valve body or marked with the flow direction of the medium.
1. Minimum wall thickness: The "minimum thickness" of the valve body and bonnet of the cryogenic valve does not accept the wall thickness in the ASMEB16.34 standard. The "minimum wall thickness" of the gate valve shall not be less than API600, the "minimum wall thickness" of the globe valve shall not be less than BS1873, and the "minimum wall thickness" of the check valve shall not be less than the "minimum wall thickness" specified by standards such as BS1868; the diameter of the valve stem shall be Meet the requirements of API 600 or BS 1873 standards.
2. Valve seat: The sealing pair of cryogenic valve products can be designed as a metal-PTFE soft seal or a metal-metal hard seal according to the working temperature and nominal pressure of the medium, but PTFE is only suitable for the working temperature of the medium higher than -73℃" When the temperature is too low, PTFE will become brittle. At the same time, PTFE is not suitable for pressure levels greater than or equal to CL1500, because when the pressure exceeds CL1500, PTFE will produce "cold flow" and affect the sealing of the valve. Hard-sealed cryogenic gate valve, stop The valve seat of the return valve and the stop valve adopts Co-Cr-W cemented carbide directly on the valve body. The valve seat and the valve body are integrated to prevent leakage due to low-temperature deformation of the valve seat and ensure the valve seat and valve body Reliability of the seal between.
3. Anti-static: When used in flammable and explosive low-temperature media, if the valve packing or gasket and seal are made of insulating materials such as PTFE, static electricity will be generated when the valve is opened and closed. The low temperature medium is very scary, so the valve should be designed with anti-static device.
Cryogenic Valve material selection:
1. The valve body and bonnet adopt: LCB (-46℃), LC3 (-101℃), CF8 (304) (-196℃).
2. Wedge: stainless steel surfacing cobalt-based cemented carbide.
3. Seat: stainless steel surfacing cobalt-based cemented carbide.
4. Stem: 0Cr18Ni9.
Cryogenic valve standards and product structure:
1. Design: API6D, JB/T7749
2. Routine inspection and test of valve: According to API598 standard.
3. Cryogenic Valve temperature inspection and test: According to JB/T7749.
4. Drive mode: manual, bevel gear drive and electric drive device.
5. Valve seat form: The valve seat adopts a welded structure, and the sealing surface is welded with cobalt-based hard alloy to ensure the sealing performance of the valve.
6. The wedge adopts an elastic structure, and a pressure relief hole is designed at the pressure inlet end.
7. One-way sealing valves are marked with flow direction signs on the valve body.
8. Cryogenic ball valves, gate valves, stop valves, and butterfly valves adopt long neck structures to protect the packing.
9. Standard for cryogenic ball valve: JB/T8861-2004.