Design and Operational Requirements of Cryogenic Electric Control Valves

In the application of electric control valves, special protective measures must be taken when operating temperatures are significantly below freezing. This is particularly important in extremely low-temperature environments, where the design and material selection of the electric control valves become crucial. This article will explore the main design requirements, material choices, structural features, operational environments, and precautions for cryogenic electric control valves to assist engineers in making informed decisions in practical applications.

Material Selection for Low-Temperature Operating Conditions

The choice of materials for electric control valves in low-temperature environments is vital. The typical operating temperature range is from -29°C to -101°C, and components that bear pressure must be made from specific impact-resistant carbon steels. Here are the recommended materials for different temperature ranges.

-29°C to -46°C: Low Carbon Steel (LCB) is typically used in this temperature range due to its excellent toughness and impact resistance, making it suitable for moderate low-temperature applications. This material can withstand significant pressure variations and impact loads, applicable in various industrial settings.

-46°C to -101°C: For even lower temperatures, steel containing 3.5% nickel is recommended. This nickel alloy steel maintains its mechanical properties and toughness in extremely low environments, ensuring the valve operates normally under harsh conditions.

For electric control valves within this temperature range, a long-neck upper valve cover is typically used. This design effectively reduces heat transfer and prevents freezing in the packing box due to low temperatures, which can affect valve operation. Generally, the long-neck upper valve cover is installed vertically to minimize heat transfer from the operating fluid into the valve body.

Materials and Structure for Cryogenic Conditions

In applications with cryogenic temperatures (below -101°C), the structural materials of electric control valves must meet the special requirements of extreme environments. Valves in this temperature range are often used to control extremely cold gases and liquefied gases, such as air, nitrogen, oxygen, and hydrogen.

Material Selection

Austenitic Stainless Steel: Known for its excellent corrosion resistance and low-temperature strength, it remains stable in extremely low temperatures.
Bronze: Offers good toughness and wear resistance at low temperatures, making it suitable for various applications.
Monel Alloy: This nickel-based alloy performs exceptionally well in extreme environments, providing excellent corrosion resistance, ideal for controlling high-purity gases and liquefied gases.
When designing the long-neck upper valve cover, even if the valve body is made of bronze, the upper valve cover is generally made of austenitic stainless steel to minimize heat conduction. It’s important to note that when closing the valve, vaporization of liquefied gas may cause gas to accumulate between the upper valve covers, leading to high pressure. Therefore, measures must be taken to prevent this occurrence.

Insulation Requirements and Special Design Features

Cryogenic electric control valves must adhere strictly to insulation requirements to ensure system safety and efficiency. In low-temperature factory areas, process equipment, pipelines, and valves are typically housed in cold boxes. In such cases, the design of the electric control valve often requires a longer upper valve cover, which can be installed horizontally.

Special Design Points

Extended Upper Valve Cover: The design of the electric control valve's upper valve cover is longer, allowing for the disassembly of internal components, such as the valve core and seat, without affecting the valve body. This design reduces the risk of cold box leaks and facilitates maintenance operations.
Material Selection and Insulation: The large-diameter upper valve cover is made of stainless steel and penetrates through the cold box wall, ensuring the valve body is not affected by the cold box, thus reducing the risk of leaks. Additionally, the valve's insulation layer should utilize high-efficiency insulating materials to minimize energy loss.

Cleanliness and Lubricant Selection

The processing and assembly of cryogenic electric control valves require strict cleanliness standards. Any impurities present can affect the valve's performance and safety, so effective measures must be taken during assembly to ensure all components are clean.

Lubricant Selection

When selecting lubricants, it is essential to ensure they are suitable for low-temperature environments and can effectively prevent wear. Specialized lubricants developed for low temperatures can reduce wear and corrosion risks.
Avoid Solidified or Brittle Lubricants: Some lubricants may solidify or become brittle at low temperatures, so it is important to choose those that remain fluid even at extremely low temperatures.
Compatibility with Fluids: The selection of lubricants must also consider their compatibility with the fluid. For example, when regulating liquid fluorine, the lubricant must not come into contact with any hydrocarbons to prevent self-ignition. In controlling oxygen, care must be taken to avoid impurities, as oxygen not only supports combustion but can also lead to severe damage in case of a fire.

Conclusion

The design and material selection of electric control valves are critical in extremely low-temperature environments. By implementing reasonable structural designs, material applications, and stringent cleanliness requirements, the safety and efficiency of valves under cryogenic conditions can be ensured. Engineers must thoroughly consider these factors in practical applications to achieve optimal system performance and safety. A deep understanding of cryogenic electric control valves will enhance their effectiveness in modern industry, providing strong support for the ongoing development of related fields.