What are cryogenic valves?
The Cryogenic valves are suitable for medium temperature – 40 °C to – 196 °C valves.
Cryogenic valves include cryogenic ball valves, cryogenic Gate valves, cryogenic shutoff valves, cryogenic safety valves, cryogenic check valves, cryogenic butterfly valves, cryogenic needle valves, cryogenic throttle valves, cryogenic pressure reducing valves, etc. They are mainly used in ethylene, liquefied natural gas installations, LPG LNG tanks, receiving bases and satellite stations, air separation equipment, Petrochemical tail gas separation equipment, liquid oxygen, liquid nitrogen, liquid argon, dioxide, etc. Carbon cryogenic storage tank and tank truck, pressure swing adsorption oxygen plant, etc. Output liquid cryogenic media such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc., are not only flammable and explosive, but also gasifiable when heating up. When gasifying, the volume expands hundreds of times.
The material of LNG valve is very important, and the unqualified material will Cause leakage or internal leakage of shell and sealing surface; the Comprehensive mechanical properties, strength and steel of Components Can not meet the use requirements or even break. The explosion was Caused by the leakage of liquefied natural gas. Therefore, in the process of developing, designing and developing liquefied natural gas valves, material quality is the most important and key issue.
- Pressure grade: 150, 300, 600 Lb, 900 LB, 1500 LB (45 MPa).
- Valve diameter: 15-1200 mm (1/2-48″).
- Connection form: flange type, welding type, thread.
- Valve material: LCB, LC3, CF8.
- Working temperature: – 46 °C, – 101 °C, – 196 °C, – 253 °C
- Applicable media: liquefied natural gas, ethylene, propylene, etc.
- Driving mode: manual, bevel gear transmission, electric.
- Design: API6D, JB/T7749
- Valve routine inspection and test: according to API 598 standard.
- Valve low temperature inspection and test: according to JB/T7749.
- Driving mode: manual, bevel gear drive and electric drive device.
- Seat type: The seats are welded with Cobalt-based Cemented Carbide overlaying on the sealing surface to ensure the sealing performance of the valves.
- The gate adopts elastic structure, and the pressure relief hole is designed at the pressure end.
- One-way sealed valve body is marked with flow direction sign.
- Low temperature ball valves, gate valves, globe valves and butterfly valves adopt long neck structure to protect packing.
- Ultra-low temperature ball valve standard: JB/T8861-2004.
- The body and Cover are LCB (-46 °C), LC3 (-101 °C) and CF8 (304) (-196 °C).
- Gate: Stainless steel surfacing Cobalt-based Cemented Carbide.
- Seat: Stainless steel surfacing Cobalt-based Cemented Carbide.
- Stem: 0Cr18Ni9.
Mostly, the cryogenic separation technique is adopted to separate cracked gas components such as hydrogen and methane in the current large or medium sized ethylene devices, and it can also be used in coal-to-methanol purification devices. In order to meet the requirement, cryogenic valves are widely used. Only by understanding the design requirements and special structures of cryogenic valves, can one make no mistake when choosing and installing the valves. And since cryogenic valves, especially ultra-low temperature valves, have extremely low operating temperatures, when designing such valves, in addition to the general valve design principles, there are some special requirements.
cryogenic valves are kept in a natural closed position to keep cryogenic gasses or other medium secure and safely contained. A cryogenic valve is generally designed to react to high pressure which pushes the valve into the open position to allow the gas or other media to flow readily through. Such open flow will continue until the pressure again decreases, at which point it will swing back nd become seal with a special metal seat bubble-tight shutoff to prevent any leaking.
The design of the cryogenic valve has the following requirements, depending on the conditions of use:
- Valves should not be a significant source of heat in cryogenic systems. This is because the inflow of heat will not only reduce the thermal efficiency, but also cause the internal fluid to evaporate rapidly when it is excessive, resulting in an abnormal pressure rise and a hazard.
- The cryogenic medium should not have a detrimental effect on the handling of the wheel and the sealing performance of the packing.
- Valve assemblies that come in direct contact with low temperature media should have explosion-proof and fire-resistant structure.
- Valve assemblies that operate at low temperatures can’t be lubricated, so structural measures are required to prevent parts from being scratched.
Strict manufacturing process and special equipment are formulated for the low-temperature valves produced, and strict quality Control is Carried out for the processing of parts. After special low-temperature treatment, rough parts are placed in Cooling medium for several hours (2-6 hours) to release stress, ensure low-temperature performance of materials, and ensure finishing size, in order to prevent valve leakage Caused by temperature Change in low-temperature working Conditions. Valves are assembled differently from ordinary valves. Parts need to be Cleaned strictly to remove any oil stains in order to ensure service performance.
Test equipment for cryogenic valves:
- Low Temperature Valve Test Device
- Liquid Nitrogen Storage Device
- cryogenic treatment tank
- Low Temperature Test Bed to Ensure the Performance of Valves under Low Temperature Conditions
Test and inspection of cryogenic valves:
The main parts of the cryogenic valve are treated at low temperature and the cryogenic impact test is Carried out on each batch of samples to ensure that the valve does not Crack at low temperature and Can withstand the impact of cryogenic medium.
Test each valve as follows:
- Strength test of shell at room temperature;
- Sealing test at room temperature and low pressure;
- Sealing test at room temperature and low pressure;
- Gas tightness test of upper seal at low temperature (with upper seal);
- Low temperature gas seal test, etc. to ensure that the whole cryogenic valve meets the requirements of the standard;
- Low temperature treatment of main Components and low temperature impact test of each batch of samples are Carried out to ensure that the valve does not Crack at low temperature and Can withstand the impact of low temperature medium.
- Low temperature (cryogenic) valves are processed and impacted according to the Corresponding material specifications.
- The electrostatic function is more powerful. The on-resistance between the valve body and the stem or between the internals and the valve body is less than 1 ohm.
Other parameters of cryogenic valves:
The valve body is light and small in size.
In order to reduce the heat loss of the valve body, especially to ensure the use of the valve at ultra-low temperature, the valve body is specially designed to be light in weight and small in size.
Long shaft valve with low temperature fluid flow through the valve, using long stem form, Can avoid the role of external heat to keep the pressure Cap at room temperature, in order to prevent the performance of the Cap seal. this
Length is the best length obtained by Calculation and experiment.
Soft sealing structure: In SW, BW form, the valve body Can not be removed from the piping in order not to replace the valve body seat using soft Contact seat. Valve Core seal is stable at low temperature
Teflon or Deflon with good properties and 15% glass fiber Can be replaced by itself as needed. Hard metal seals: metal seals for gate valves and fire protection requirements
On the valve. It is to add W-Cr-Co alloy metal bushing on the Contact surface of the valve seat to improve the surface hardness, anti-burn and wear resistance.
Gasification boost structure gate valve adopts flexible structure and implements all sealing. Therefore, the liquefied gas inside the valve body is sealed when it absorbs external heat and the temperature rises.
The phenomenon of re-gasification will occur, which will Cause the normal pressure rise inside the valve. In order to prevent this phenomenon, a pressure relief hole is arranged on the valve Core. Excellent durability
Teflon ring packing with good durability in Nanchang is used in the pressing part of the packing. The filler Can be self-pressurized and sealed by internal pressure, so a smaller tightening force is used.
Moments Can be easily Controlled. And the friction is small, so the operation is light.
Gasket gasket is made of Teflon material with stable sealing Ceramic filling material. In addition, the right of use is frequently Converted to normal temperature and low temperature.
And gaskets with scroll metal surface wrapped around the sealing stability of temperature Change.
There are two main situations, one is internal leakage, the other is external leakage.
The main Cause of valve internal leakage is the deformation of sealing pair at low temperature. When the temperature of the medium drops to phase Change, the volume Changes, warping deformation occurs on the sealing surface with high grinding accuracy, which results in poor cryogenic sealing.
Leakage of valves: First, when flanged Connection is used between valves and pipelines, it will lead to leakage due to the relaxation of the Connection pads, bolts, and the asynchronous shrinkage of the Connectors between materials at low temperature. Therefore, the Connection mode between valve body and pipeline Can be Changed from flange Connection to welding structure to avoid low temperature leakage. The second is the leakage of valve stem and packing.
There are five types of cryogenic valves that are ideal for cryogenic media. Each of these types has its own set of characteristics that make them suitable in some applications and unsuitable in others.
- Globe valves: called such due to their spherical shape, these valves have an internal movable disc — the obturator — that rotates at 90 degrees to the plane of its coordinated body seat. These cryogenic valves offer greater reliability for long-term sealing performance but are susceptible to moisture and aren’t good in situations where flow rate is paramount.
- Ball valves: these valves utilize a ball as the obturator and generally include a Polytetrafluoroethylene body seat. They have better flow characteristics than globe valves but are more prone to wear and tear along its seals and the ball itself. They are thus most valuable for applications in which an unrestricted flow path is necessary.
- Top entry ball valves: similar to standard ball cryogenic valves, this newer model has a one-piece design with butt welded connections that makes maintenance easy. The lack of mechanical joints also makes it a preferred option in fire safe applications.
- Gate valves: gate valves utilize a wedge-type gate as the obturator which swings to close parallel to the mating body seat. They’re similar to ball valves in that they offer good flow characteristics but are hampered by wear and tear.
- Butterfly valves: butterfly valves are a part of the quarter turn family and utilize a circular disk at their center. This disc allows butterfly cryogenic valves to be shorter in length than the aforementioned choices, making them lighter and cheaper as well as quick and simple to operate. But over-use leads to their shorter lifspan.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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