Common raw materials for alloy steel pipe fittings are mainly classified by their chemical composition (such as content of chromium, molybdenum, nickel, vanadium, etc.) and manufacturing process. They are widely used in special working conditions including high temperature, high pressure, low temperature or severe corrosion. Detailed classifications are as follows:
1. Chrome-Molybdenum Heat-Resistant Steel (Cr-Mo Steel)
This is the most widely used alloy steel material for pipe fittings in petrochemical and power industries, mainly for high-temperature and high-pressure service.
- 15CrMoG / 15CrMoR: Pearlitic heat-resistant steel. “G” stands for pipe material and “R” for plate material. Containing chromium and molybdenum, it effectively resists oxidation and creep at high temperatures. Commonly used for medium‑high‑temperature pipelines in refineries and fertilizer plants, as well as superheater fittings for high-pressure boilers.
- 12Cr1MoVG: Superior to 15CrMo in performance, with vanadium (V) added to further enhance high-temperature strength and long-term ductility. It is the primary material for main steam and reheat steam pipe fittings in large generating units (300MW, 600MW).
- P91 / T91 (F91): Martensitic heat-resistant steel. A high-chromium (9% Cr) alloy steel with extremely high high-temperature strength and oxidation resistance. Suitable for high-temperature and high-pressure pipe fittings in ultra-supercritical power units (above 600℃), serving as a key material for modern power plants.
- P22 / T22 (F22): Cr-Mo-V steel with performance between 15CrMo and P91, used for medium temperature and pressure conditions.
2. Austenitic Stainless Steel
Mainly used in corrosive and low-temperature environments, with excellent toughness and weldability.
- 304 / 304L: The most general-purpose stainless steel. 304 provides good corrosion and heat resistance; 304L is the low-carbon version, mainly to prevent intergranular corrosion during welding. Widely used for pipe fittings handling general corrosive media in chemical, food and pharmaceutical industries.
- 316 / 316L: Molybdenum (Mo) added on the basis of 304, offering excellent corrosion resistance to chloride ions (e.g., seawater, brine) and reducing acids such as sulfuric acid. 316L is also low-carbon, commonly used for pipe fittings in seawater desalination, marine engineering and high-end chemical equipment.
- 321: Stabilized with titanium (Ti), specially designed to resist intergranular corrosion at high temperatures, often used for pipe fittings in high-temperature heating furnaces.
3. Low-Temperature Nickel Steel
Specially used in extremely cold environments to prevent brittle fracture of materials at low temperatures.
- 09MnNiDR: A common steel for low-temperature pressure vessels containing trace nickel. It maintains good impact toughness at low temperatures from -40℃ to -70℃, widely used for pipe fittings in LNG, liquid nitrogen and liquid oxygen transmission pipelines.
- 3.5Ni / 9Ni steel: Alloy steels with higher nickel content, used for pipe fittings in cryogenic environments down to -100℃ or even -196℃ (liquid nitrogen temperature).
4. Low-Alloy High-Strength Steel
Although total alloy content is relatively low (generally < 5%), its strength is much higher than ordinary carbon steel. Often used for large-diameter, thick-walled high-pressure pipe fittings.
- Q345R (formerly 16MnR): The most commonly used low-alloy high-strength steel. With good comprehensive mechanical properties and weldability, it is widely used for large-diameter elbows, tees and flanges for medium‑low‑pressure vessels and pipelines.
- Q370R / Q420R: Higher-strength low-alloy steels used for pipe fittings in large high-pressure equipment to reduce weight and improve load-bearing capacity.
5. Duplex Stainless Steel
Combines the advantages of austenitic and ferritic stainless steels, with extremely high strength and corrosion resistance.
- 2205 (S32205): The most commonly used duplex stainless steel. Its yield strength is twice that of ordinary stainless steel, and it has excellent resistance to chloride stress corrosion cracking. Widely used for pipe fittings in oil and gas pipelines and seawater treatment equipment.
Summary
- High temperature and high pressure: choose Cr-Mo steel (e.g., 15CrMo, P91).
- Corrosive environment: choose stainless steel (e.g., 304, 316L).
- Extremely low temperature: choose nickel steel (e.g., 09MnNiDR).
- Large-diameter load-bearing: choose low-alloy steel (e.g., Q345R).
