Piping systems that use liquid hydrogen, oxygen, helium, nitrogen, liquefied natural gas, or similar very cold liquids require the use of refrigeration valves. The term cryogenic refers to materials and processes below -1010C (-2390F). Therefore, refrigeration valves must be designed with features that can withstand such low temperatures. The main difference between refrigeration valves and standard valves is that they are able to operate at such low temperatures and high pressures.
Problems with cryogenic or cryogenic valves
The main problem with cryogenic valves is that any leakage of liquids into the atmosphere through washers or seals reduces the performance of the valve and related equipment. Also, such a leak in the milk stalk causes local freezing, which may interfere with the milk’s working mechanism. This is because refrigeration application valves must be designed for high performance and zero leakage in accordance with API 598.
Codes and standards for cryogenic valves
Codes and standards used for refrigeration valves are:
- BS 6364
- BS EN 12567
- BS EN 1626
- BS EN 12300
- MSS SP-134
- ISO 28921-1
- ISO 21011
- ISO 10497
- ASME B16.34
Why do cryogenic lions have long stems?
All cryogenic valves are specifically designed for liquefied natural gases, methane, oxygen, ammonia, etc. Cryogenic valves usually have elongated caps so that the valve seals are kept away from the cold source. This serves two important purposes:
- The milk stem seal will have a relatively higher temperature.
- There will be enough space to create insulation between the pipeline and the valve lever.
Size and degree of pressure of refrigeration valves
Refrigeration valves for industrial applications can be found in different sizes and pressure classes. The size usually varies from 8.1 inches to 88 inches (3 mm to 2240 mm). The pressure degree of refrigeration valves varies from vacuum pressure up to 700 bar. All of these valves are capable of operating at temperatures down to -2540 ° C (-4250F).
Ingredients for refrigerated milk
Common materials used to make refrigerated milk include aluminum, monel, brass, bronze, stainless steel, incoly, zirconium, and more. PTFE or graphite is commonly used as a sealant.
Common valves for cryogenic applications
Common valves used for cryogenic applications are special valve valves, parasitic valves, gate valves, and butterfly valves. Therefore, choosing the right type of cryogenic milk for the application is essential. There are no exact instructions for the type of valve in the freezing service. However, there is a way to choose between four-wheel hub valves and three-offset butterfly valves.
Offset triple butterfly valves for freezing services:
Triple butterfly valves are high performance valves that are widely used for freezing services. Displacement in such valves causes wear between the seat and the seal.
The triple offset design features a flexible stainless steel ring mounted on the disc assembly to create a zero leakage seal for refrigeration work.
The seal and the contact surface of the seat are conical. These cones are sloping and the contact angle between the seat and the seal creates a slight wedge effect that bends the disc seal ring and compresses it radially. Regardless of the direction of flow or line pressure, the valve offers excellent shut-off capability.
Ball valves for refrigeration:
Piping and piping systems for LPG, LNG, thermal fluids and liquid oxygen, nitrogen applications use double-sealed ball valves They can be reduced and complete. Cryogenic ball valves have a steam space with sufficient height that allows gas supply to the gland area. This causes the gland to pack at close ambient temperature.
With increasing pipe size, setting up gate and globe valves is difficult and expensive. This is why they are limited in size to smaller tubes and applications that do not require remote operation.
Features of refrigeration valves
Refrigeration valves should be light because the mass of light valves cools more easily from ambient temperature to cryogenic.
Lighter refrigerator valves are usually less conductive, which helps reduce heat infiltration compared to heavier structures.
Flange and welded configurations are commonly used for cryogenic pipe connections. However, boiled milk is better.
Refrigeration valves should be assembled in a clean room and have no lubricant or use cold service compatible lubricants. When purchasing a refrigeration valve, documented cleaning methods must be collected to confirm and follow appropriate procedures during assembly.
Refrigerant milk testing
The following tests are usually required for cryogenic milk:
- Shell strength test : hydrostatic or pneumatic test up to 1.5% of maximum working pressure.
- Shell leak test : To test the shell leak, a pneumatic test with a maximum working pressure of 1.1% is usually performed.
- Seat leak test: Pneumatic test up to 1.1. Maximum working pressure.
- Cryogenic prototype test : This test is performed under BS 6364 Appendix A.
- Cryogenic production test : Valve cryogenic test methods are provided in BS 6364 and are followed.
Applications of refrigeration valves
Refrigeration valves are widely used in
- LNG liquefaction plants
- LNG terminals
- LNG transportation systems
- Food and beverage industry
- Air separation plan
- Steel mills
- Research laboratories
- Chemical and petrochemical plants
- Aerospace storage facilities
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