Valves in different industrial fields and application scenarios require appropriate material selection based on media characteristics, operating pressure, and temperature. The following is an introduction to commonly used valve materials:
Metal Materials
- Cast Iron
Gray cast iron: Low cost, excellent castability and machinability, high compressive strength, but poor toughness and ductility. Suitable for conveying low-pressure fluids such as water, gas, and steam with nominal pressures ≤ 1.6 MPa and temperatures between -10°C and 200°C. Gray cast iron is often used in valves for municipal heating systems, where strength requirements are less stringent.
Ductile iron: Graphite is spherical and offers mechanical properties far superior to gray cast iron, with excellent toughness, impact resistance, and corrosion resistance. Commonly used for conveying media such as water, oil, and natural gas with nominal pressures ≤ 4.0 MPa and temperatures between -30°C and 350°C, such as large-diameter valves in municipal water supply systems.
- Carbon Steel
WCB Carbon Steel: Widely applicable, with excellent overall mechanical properties, capable of withstanding high pressures and temperatures. Suitable for use with media such as steam, water, and oil at nominal pressures ≤ 25.0 MPa and temperatures between -29°C and 425°C. For example, many valves in petrochemical pipelines are made of WCB carbon steel.
WC6 and WC9 alloy steels: Containing alloying elements such as chromium and molybdenum, they offer superior high-temperature strength, oxidation resistance, and corrosion resistance compared to ordinary carbon steel. They are commonly used in high-temperature, high-pressure steam systems, such as steam pipe valves in thermal power plants, with operating temperatures reaching 540°C or higher.
- Stainless Steel
304 stainless steel: Contains 18% chromium and 8% nickel, offering excellent corrosion resistance, heat resistance, and processability. It is suitable for use with generally corrosive media, such as the transportation of mildly corrosive liquids in the food and beverage industry, and for water supply and drainage systems in some residential buildings.
316 stainless steel: Contains 2-3% molybdenum and offers superior resistance to pitting, intergranular, and chloride corrosion compared to 304 stainless steel. Commonly used for handling highly corrosive media, such as pipe valves used to transport corrosive liquids like sulfuric acid and acetic acid in the chemical industry.
- Copper and Copper Alloys
Pure Copper (Red Copper): Excellent electrical and thermal conductivity, strong corrosion resistance, and high plasticity, but relatively low strength. It is commonly used in instrumentation, cryogenic equipment, and for transporting specialized media such as oxygen and acetylene, as it produces no sparks and offers high safety.
Brass (Copper-Zinc Alloy): Mechanical properties surpass pure copper, with excellent castability and a relatively low price. It is commonly used in water supply and drainage valves in residential buildings, such as faucets and triangular valves. It is also used for low-pressure fluid transport where corrosion resistance is less critical.
Bronze (Copper-Tin Alloys, etc.): Features high strength, hardness, and good wear and corrosion resistance. Suitable for media such as seawater and steam, such as seawater pipeline valves in the marine industry.
- Alloy Steel
Chromium-Molybdenum Alloy Steel: Contains chromium and molybdenum, offering excellent high-temperature strength, oxidation resistance, and creep resistance. Commonly used in high-temperature, high-pressure applications with demanding material properties, such as valves in refinery hydrogenation units, which can operate at temperatures exceeding 550°C.
Duplex stainless steel: Composed of both austenite and ferrite phases, it combines the advantages of both, offering high strength and excellent corrosion resistance, particularly outstanding resistance to chloride stress corrosion cracking. It is commonly used in harsh corrosive environments such as marine engineering and the chemical industry, such as valves on offshore oil platforms.
Non-metallic Materials
- Plastic
Plastic polypropylene (PP): Offers excellent corrosion resistance, low density, and excellent insulation, but lacks high heat resistance. Suitable for transporting corrosive media such as acids and alkalis at temperatures ≤90°C, such as small pipeline valves in the chemical and electroplating industries.
Polyvinyl chloride (PVC): Low cost, excellent corrosion resistance, and good mechanical properties, but limited high-temperature resistance. Commonly used in building water supply and drainage, agricultural irrigation, and other applications to transport ambient-temperature liquids, such as valves in household drainage pipes.
Chlorinated polyvinyl chloride (CPVC): Compared to PVC, it offers improved heat resistance and can operate at higher temperatures while maintaining excellent corrosion resistance. Commonly used in hot water supply systems and fire protection piping, operating temperatures can reach around 100°C.
Polytetrafluoroethylene (PTFE): Extremely chemically stable, resistant to almost all chemical media, with a low coefficient of friction and excellent self-lubrication, but also exhibits low mechanical strength and a high coefficient of linear expansion. It is often used as a sealing material or lining for valves handling highly corrosive media, such as valves handling highly corrosive liquids like aqua regia in the chemical industry.
- Ceramics
Ordinary ceramics: High hardness, good wear and corrosion resistance, but also brittle and weak against impact. Commonly used in small-diameter, low-pressure applications with highly corrosive and abrasive media, such as valves for conveying fiber-containing slurries in the papermaking industry.
Engineering ceramics: Such as alumina ceramics and silicon carbide ceramics offer superior mechanical properties, thermal stability, and chemical stability compared to ordinary ceramics. They are often used in harsh operating conditions with high temperatures, high pressures, severe corrosion, and high wear, such as valves for conveying high-temperature slag in the metallurgical industry.
