Will Seamless Steel Pipes be Affected by Low-temperature Environments?

Seamless steel pipes (SMLS) will be affected by low-temperature environments, mainly in terms of changes in material properties and safety. Specific measures are needed. Not all seamless steel pipes are suitable for low-temperature environments; materials with specific low-temperature toughness must be selected.

Low-temperature brittleness:

Steel has good ductility at room temperature and deforms (plastic deformation) before fracturing upon impact. However, as the temperature decreases, some steels transition from a ductile state to a brittle state. In the brittle state, steel cannot absorb energy through deformation and is prone to sudden low-stress brittle fracture at stress concentration points (such as notches and welds). There are almost no obvious signs before fracture, which is extremely dangerous.

Low-temperature environments can cause cold brittleness in steel pipes, especially ordinary low-carbon seamless steel pipes. At low temperatures (usually below -20℃), tensile strength and toughness decrease, making them prone to brittle fracture and unable to withstand external impacts or pressure fluctuations, posing safety hazards.

Key Influencing Factors:

1. Chemical Composition and Heat Treatment of the Material

This is the most critical factor determining the low-temperature performance of steel pipes.

Carbon Content: Higher carbon content results in harder steel but lower toughness. Low-temperature steels typically require lower carbon content.

Alloying Elements: Adding nickel (Ni) is the most effective way to improve low-temperature toughness. Higher nickel content allows the steel to withstand lower temperatures.

Heat Treatment: Heat treatment processes such as normalizing and quenching + tempering can refine the grain structure, greatly improving the low-temperature toughness of the steel.

2. Operating Temperature
Different design temperatures correspond to different material grades. The lower the temperature, the higher the requirements for the material.

How to Choose the Material for Low-Temperature Seamless Pipes?

For use in low-temperature environments, materials with good low-temperature toughness should be selected, such as low-temperature special alloy steel pipes (e.g., nickel steel). These steel pipes improve low-temperature mechanical properties by adding alloying elements, maintaining good toughness and strength even at -40℃ or lower temperatures, avoiding cold brittle fracture.

In engineering, materials are selected based on the lowest design metal temperature. Here are some common international standards:

ASTM A333 Gr. 6: 0℃ to -50℃
One of the most commonly used cryogenic pipes. The lower limit of the operating temperature is approximately -45℃. Toughness is ensured through normalizing.

ASTM A333 Gr. 3 (containing 3.5% nickel): -50℃ to -100℃
Contains approximately 3.5% nickel for use in even lower temperature environments.

ASTM A333 Gr. 8 (containing 9% nickel): -100℃ to -196℃
Contains approximately 9% nickel, a key material for cryogenic environments such as liquefied natural gas (LNG).

Austenitic stainless steel (e.g., 304/304L, 316/316L) or aluminum alloys: Below -196℃
Carbon steel is insufficient at this temperature. Austenitic stainless steel maintains good toughness at extremely low temperatures.

Precautions for Use:

During use, care must be taken to avoid subjecting the steel pipes to severe impacts or sudden pressure in low-temperature environments to prevent damage caused by decreased material toughness. Regularly inspect the appearance and performance of the steel pipes; if surface cracks or a decline in mechanical properties are found, replace them immediately.

Furthermore, seals at steel pipe joints are prone to hardening and failure in low-temperature environments. Low-temperature compatible seals must be selected to ensure airtightness, prevent media leakage, and guarantee safe use in low-temperature environments.

Read more: ASTM A333 Low Temperature Steel Pipe or Schedule 40 vs Schedule 80 Pipe

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