Design and Structural Features of Low-Temperature Valves

Low-temperature valves play a crucial role in industries such as fertilizers, liquefied natural gas (LNG), and petrochemicals. These valves are essential for controlling liquid nitrogen and other inert gases, and they are widely used in handling flammable, explosive, and easily vaporizing substances. Since these materials can rapidly vaporize and expand in volume when heated or during flashing, the design of low-temperature valves must prioritize safety, reliability, and durability to withstand extreme working conditions.

Definition and Classification

According to industry standards, low-temperature valves are those used in environments where the medium temperature is below -40°C, while ultra-low temperature valves are suitable for temperatures below -101°C. The design of these valves involves careful material selection and a strong focus on structural integrity and safety to ensure effective operation at very low temperatures.

Structural Design Features

The structural design of low-temperature valves is essential for their functionality and safety. Here are some key design features.

1. Extended Bonnet

 
The extended bonnet is one of the most notable design features of low-temperature valves. This design moves the operating handle and packing structure away from the low-temperature zone, offering several advantages.
 
Preventing Frostbite: The extended bonnet places the operating parts at a higher temperature, reducing the risk of injury to operators, especially in extremely cold environments.

Prolonging Packing Lifespan: By operating at normal temperatures, the packing maintains its sealing performance, preventing leaks caused by packing failure and ensuring long-term stability of the valve.
 
Facilitating Insulation Material Application: The extended bonnet structure minimizes cold energy loss and makes it easier to install insulation materials. The packing gland is positioned outside the insulation layer, allowing for easy tightening of gland bolts or adding packing without damaging the insulation.

2. Drip Plate Structure

To reduce heat transfer from low-temperature media to the valve stem and packing material, many low-temperature valves feature a drip plate structure. The advantages of this design include:

Corrosion Prevention: The drip plate effectively prevents condensed water vapor from dripping onto the valve's flange bolts, reducing corrosion risk and extending the equipment's lifespan.
Protects Insulation Layer: Positioned outside the insulation layer, the drip plate prevents condensation from falling on the insulation and valve body, helping to maintain cold retention.
Self-Relieving Pressure Structure When dealing with flammable, explosive, or easily vaporizing media, the sealing structure of low-temperature valves must incorporate special designs. Many valves are equipped with a self-relieving pressure structure to prevent internal overpressure:
Automatic Release: When internal pressure rises abnormally, the self-relieving structure automatically releases pressure, preventing media leaks or fire incidents. This design varies significantly among different valve types (e.g., gate valves, ball valves).
Flexible Sealing Structure: Different valve types may have unique pressure relief designs. Manufacturers optimize these based on the specific sealing principles of the valves to ensure safety.

3. Anti-Static and Fire Protection Design

Given that low-temperature valves are typically used with flammable and explosive media, anti-static and fire protection designs are particularly important:
Anti-Static Design: By electrically connecting the valve stem to the valve body, static electricity buildup is eliminated, reducing safety hazards. This design often utilizes conductive materials or grounding measures to ensure timely discharge of static.
Fire Protection Structure: To address potential leaks caused by extreme temperature changes, the fire protection design must meet industry standards, including the use of high-temperature materials and fire barriers. This design effectively reduces fire risks, protecting both equipment and personnel.

Material Selection and Performance

The choice of materials for low-temperature valves is crucial for their performance. Common materials include low-temperature carbon steel and austenitic stainless steel.

Low-Temperature Carbon Steel: Suitable for valves operating at -46°C, it offers good strength and toughness, maintaining reliability in low-temperature conditions.
Austenitic Stainless Steel (300 Series): Used in valves for -101°C and -196°C environments, this material has excellent low-temperature impact toughness and effectively resists brittleness. It also offers good corrosion resistance and processability, making it ideal for applications requiring high strength and durability.

Maintenance and Operational Considerations

Regular inspection and maintenance are key to ensuring the long-term stable operation of low-temperature valves. Operators should routinely check the valve's sealing performance and the condition of the packing to prevent leaks due to aging or damage. During operation, staff should follow relevant procedures to ensure the safe and effective functioning of the valves. Additionally, operators should receive professional training to understand the characteristics of low-temperature valves and best practices for specific applications.

Conclusion

The design of low-temperature valves is not only about material selection and structural integrity but also closely tied to their safety and reliability in extreme environments. By continually optimizing designs and enhancing material performance, low-temperature valves will continue to play a critical role in the chemical, oil, and gas industries, ensuring safe and efficient industrial operations. As the industry evolves, the technology behind low-temperature valves will also advance, meeting increasingly stringent safety and performance requirements and driving ongoing progress in the field.