Materials for low-temperature service are mainly classified according to their minimum service temperature and chemical composition. They are explained below in accordance with commonly used international standards (ASTM) and Chinese national standards (GB), without using tables.
I. Common Low-Temperature Steel Grades under International Standards (ASTM)
1. Nickel-Based Low-Temperature Steels (Most Widely Used)
Nickel is the most effective element for improving low-temperature toughness, making nickel steels the preferred materials for cryogenic service.
- A420 WPL3Contains 1.5% nickel, with a minimum service temperature of -73°C. Commonly used for general low-temperature pipelines and chemical processing units.
- A420 WPL6Contains 3.5% nickel, with a minimum service temperature of -101°C. It is the most commonly used pipe fitting material in liquefied natural gas (LNG) and ethylene plants.
- A350 LF3Contains 3.5% nickel, with a minimum service temperature of -101°C. Mainly used for low-temperature flanges and forged fittings.
- A353With 5% nickel, the minimum service temperature can reach -129°C; with 9% nickel, it can reach -196°C. 9% nickel steel is a key material for LNG storage tanks and cryogenic vessels.
2. Improved Carbon Steels for Low-Temperature Service
Low-temperature toughness is enhanced by reducing carbon content, strictly controlling impurities, and refining grains.
- A350 LF2An improved carbon steel grade, with a minimum service temperature of -46°C. Widely used for low-temperature pressure vessels, flanges and pipe fittings.
- A516 Gr. 60 / Gr. 70Mainly steel plates for pressure vessels, with a minimum service temperature of -46°C. They feature good low-temperature impact toughness and weldability.
- A234 WPBOrdinary carbon steel, with a typical minimum service temperature of -29°C. Suitable for low-temperature applications with moderate requirements.
3. Austenitic Stainless Steels (Extreme Low Temperatures)
Austenitic stainless steels do not become brittle at low temperatures; instead, their toughness increases, allowing them to be used in environments near absolute zero.
- 304 / 304LMinimum service temperature up to -270°C. Suitable for cryogenic equipment such as liquid nitrogen and liquid oxygen systems.
- 316 / 316LMinimum service temperature up to -270°C. With molybdenum addition, they offer better corrosion resistance, ideal for corrosive low-temperature environments.
- 321Minimum service temperature up to -270°C. Stabilized with titanium to prevent intergranular corrosion, suitable for applications where heat treatment is not feasible after welding.
II. Common Low-Temperature Steel Grades under Chinese National Standards (GB)
1. Nickel-Based Low-Temperature Steels
- 09MnNiDCorresponds to ASTM A420 WPL6, with a minimum service temperature ranging from -70°C to -100°C. Widely used for LNG pipelines and low-temperature pipe fittings.
- 16MnDRCorresponds to ASTM A516 Gr. 70, with a minimum service temperature of -40°C. A commonly used steel plate for low-temperature pressure vessels.
- 06Ni9Corresponds to ASTM 9% nickel steel, with a minimum service temperature of -196°C. Mainly used for LNG storage tanks.
2. Low-Alloy Low-Temperature Steels
- Q345D / Q345EQ345D has a minimum service temperature of -20°C, while Q345E reaches -40°C. Often used for low-temperature structural parts and pipelines.
- Q390D / Q390EMinimum service temperature ranging from -20°C to -40°C, classified as high-strength low-temperature structural steels.
3. Stainless Steels (for Low-Temperature Service)
- 06Cr19Ni10 (304)Corresponds to ASTM 304, minimum service temperature -270°C.
- 022Cr19Ni10 (304L)Corresponds to ASTM 304L, minimum service temperature -270°C.
- 06Cr17Ni12Mo2 (316)Corresponds to ASTM 316, minimum service temperature -270°C.
III. Key Performance Requirements for Low-Temperature Steels
Steels for low-temperature service must meet the following core performance requirements:
- Good low-temperature impact toughnessSufficient toughness must be maintained at the service temperature to avoid brittle fracture. Low-temperature impact energy is generally required to be no less than 27J.
- Low Nil-Ductility Transition (NDT) temperatureBrittle fracture does not occur above the NDT temperature, so the NDT temperature must be lower than the service temperature.
- Strict chemical composition controlCarbon content is reduced to improve toughness; impurities such as sulfur and phosphorus are tightly controlled; elements such as nickel, manganese and vanadium are added to enhance low-temperature properties.
- Grain refinementGrain refinement through heat treatment processes such as normalizing and quenching-and-tempering to improve low-temperature toughness.
IV. Typical Application Scenarios and Material Selection Recommendations
- General low-temperature pipelines (-20°C to -40°C)A350 LF2 or 16MnDR is recommended.
- Ethylene plants (-70°C to -100°C)A420 WPL6 or 09MnNiD is recommended.
- LNG storage tanks and pipelines (-162°C)9% nickel steel (A353 9Ni or 06Ni9) is recommended.
- Cryogenic environments such as liquid nitrogen and liquid oxygen (-196°C)304L or 316L austenitic stainless steel is recommended.
- Cryogenic test equipment (-269°C, liquid helium)Austenitic stainless steels such as 304L and 316L must be used.
