Common Non-Metallic Materials Used in Control Valves
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In industrial processes, the selection of materials for control valves is not only crucial for their performance but also significantly impacts their reliability and durability under varying conditions. As operational environments become more complex, especially with high temperatures, pressures, corrosive, and abrasive media, non-metallic materials have gained prominence due to their excellent chemical stability, corrosion resistance, and flexibility. Choosing the right non-metallic material can extend the lifespan of a control valve, reduce maintenance costs, and ensure the continuous and stable operation of equipment. This article explores several common non-metallic materials, examining their properties, applications, and advantages.
Nitrile Rubber
Nitrile rubber (Buna-N or NBR) has a working temperature range of -18°C to 100°C and is a versatile material widely used in industrial control valves. It is especially suitable for applications involving contact with water, gases, petroleum, and lubricants. NBR is also known for its good wear resistance and ability to resist deformation, making it ideal for valves that require frequent operation. However, it is not suitable for use with gasoline containing paint additives or other corrosive solvents.
Main Applications: Commonly used in control valves for fuel, LPG, glycol, low-pressure gas, and lubricating oils.
Food-Grade NBR: With a working temperature range of -18°C to 82°C, food-grade nitrile rubber complies with CFR 21 Part 177.2600 standards, making it suitable for FDA-approved applications in food processing equipment to ensure the safety of valve seats in contact with food or beverages.
Ethylene Propylene Diene Monomer (EPDM)
With a temperature rating of -28°C to 120°C, EPDM is a copolymer of ethylene, propylene, and a diene component. It exhibits excellent aging resistance, ozone resistance, and weatherability, making it particularly suitable for outdoor use or in systems involving polar solvents. EPDM is widely used in HVAC systems, cooling water systems, and pipelines carrying glycol or phosphate esters. Its electrical insulation properties also make it useful for anti-static equipment.
Main Applications: HVAC systems, cooling water systems in chemical processing, and pipelines carrying glycol and phosphate esters.
Limitations: EPDM is not suitable for valves used with hydrocarbon solvents, oils, or petroleum-based products, as it degrades rapidly when exposed to substances like chlorinated hydrocarbons or turpentine.
Food-Grade EPDM: The temperature range is the same as regular EPDM and is suited for food processing and pharmaceutical industries requiring FDA compliance.
Polytetrafluoroethylene (PTFE)
PTFE, with a working temperature range of -32°C to 200°C, is renowned for its high-temperature resistance, chemical corrosion resistance, and low friction coefficient. Due to its chemically inert nature, PTFE is resistant to nearly all chemical media, making it ideal for control valves handling corrosive substances like strong acids and bases. Its low friction also makes it a preferred sealing material for precision valves.
Main Applications: Valves in chemical industries transporting strong acids, bases, and solvents, especially in high-temperature and corrosive environments.
Conductive PTFE: Designed to allow current flow, conductive PTFE is used in applications where static discharge is a concern, although it cannot pass spark tests for quality inspection.
Reinforced PTFE (RTFE): By adding materials like glass fiber, graphite, or carbon fiber to PTFE, its mechanical properties are enhanced, improving wear resistance and deformation strength. RTFE is widely used in high-load, high-wear applications.
Fluoroelastomer (Viton)
Fluoroelastomer (Viton) has a working temperature range of -18°C to 150°C and offers excellent resistance to high temperatures and chemical corrosion, particularly in contact with hydrocarbons, mineral acids, and high-temperature gases. Due to its stability in harsh environments, Viton is commonly used in valves for chemical, petroleum, and fuel-related industries. However, Viton performs poorly in steam and water applications, making it unsuitable for those media.
Main Applications: Valves used in petroleum, chemical, and fuel pipelines, but not recommended for steam or water applications.
Ultra-High-Molecular-Weight Polyethylene (UHMWPE)
UHMWPE has a working temperature range of -32°C to 88°C and performs better than PTFE in low-temperature environments. It also offers good wear resistance and chemical resistance, making it suitable for control valves in high-wear, low-temperature applications.
Main Applications: Ideal for high-wear, high-impact environments such as valves used in mining and wastewater treatment systems.
Silicone Rubber
Silicone rubber, with a working temperature range of -100°C to 300°C, is noted for its excellent heat resistance and electrical insulation properties. It is chemically inert and resistant to organic acids and low-concentration inorganic acids, making it suitable for extreme environments. However, silicone rubber has relatively low mechanical strength and often requires post-curing to enhance its performance.
Main Applications: Used in high-temperature and electrically insulating industrial valves, particularly in the chemical, electronics, and food processing sectors.
Graphite
Graphite is a non-metallic material that offers exceptional high-temperature resistance, conductivity, and self-lubrication. With a melting point as high as 3600°C, graphite retains its strength and oxidation resistance even under extreme temperatures. It is often used for valve gaskets, packing, and seats, especially in high-temperature, high-pressure, and highly corrosive environments.
Main Applications: Commonly used as sealing material in high-temperature, high-pressure environments such as nuclear power plants and petrochemical equipment.
Conclusion
Each non-metallic material offers unique advantages and limitations in control valve applications. NBR is ideal for common media like water and oil, while PTFE and Viton excel in high-temperature and corrosive environments. EPDM is suitable for outdoor applications, and UHMWPE is perfect for high-wear conditions. Silicone rubber and graphite are the go-to materials for extreme temperatures. Selecting the appropriate material based on operational conditions, media, and temperature range can significantly improve valve performance and lifespan, ensuring the safe and stable operation of industrial processes.