Low-temperature steel pipe fittings are mainly used in piping systems operating below 0℃, especially at -20℃, -40℃ or even lower temperatures (such as -196℃). The core requirement for these materials is extremely high low-temperature impact toughness to prevent brittle fracture at low temperatures. According to different service temperatures, commonly used raw materials are divided into the following categories:
1. Nickel-based low-temperature steels (most widely used with stable performance)
This is the most widely used series for low-temperature pipe fittings. Adding nickel (Ni) significantly improves toughness and lowers the ductile-brittle transition temperature.
- 2.5% nickel steel (e.g. 06Ni3.5): Suitable for environments from -45℃ to -101℃. Commonly used for low-temperature pipe fittings in liquefied petroleum gas (LPG) and ethylene plants.
- 3.5% nickel steel (e.g. 08Ni3.5): Suitable for -101℃ to -107℃. A common material for large low-temperature spherical tanks and piping fittings.
- 9% nickel steel (e.g. 06Ni9): A classic cryogenic steel suitable for -196℃ (liquid nitrogen temperature). It is the key material for pipe fittings in LNG carriers, storage tanks and transmission pipelines, maintaining excellent toughness under cryogenic conditions.
2. High-manganese austenitic low-temperature steels
These steels use manganese (Mn) and nitrogen (N) to maintain an austenitic structure at room and low temperatures, providing excellent low-temperature toughness.
- 16MnDR (steel for low-temperature pressure vessels): The most basic low-temperature steel, belonging to high-strength low-alloy steel. Suitable for -40℃ environments. Widely used for pipe fittings in oil and gas pipelines, boilers and pressure vessels in cold northern regions.
- 09MnNiDR: Improved on the basis of 16MnDR with nickel added. Suitable for -70℃ environments. Widely applied in pipe fittings for coal chemical and low-temperature separation equipment.
- 06MnNbDR: Suitable for -45℃. Niobium (Nb) is added to refine grains and improve strength and toughness.
3. Austenitic stainless steels (cryogenic and highly corrosive environments)
Although usually classified as stainless steels, they are also excellent low-temperature materials, as the austenitic structure is non-magnetic and does not embrittle near absolute zero.
- 304 / 304L stainless steel: Suitable for -196℃ to -270℃. Strength increases under cryogenic conditions with good corrosion resistance. Commonly used for pipe fittings in chemical cryogenic separation units.
- 316 / 316L stainless steel: Suitable for below -196℃. In addition to low-temperature resistance, it also resists chloride ion corrosion, used for cryogenic pipelines with corrosive media.
4. Aluminum alloys (special ultra-low-temperature applications)
Aluminum alloys are also common raw materials for pipe fittings in certain special scientific experiments or aerospace fields where weight is sensitive and temperatures are extremely low (such as -269℃ liquid helium service).
- 5083 aluminum alloy: Features good low-temperature performance, corrosion resistance and low density, often used in lightweight low-temperature piping systems.
Summary
- General cold regions (-40℃): 16MnDR is preferred.
- Medium cryogenic service (-70℃ to -100℃): 09MnNiDR or 3.5% nickel steel is commonly used.
- Cryogenic service (-196℃ LNG): 9% nickel steel or 304 stainless steel must be used.
