Analysis of materials and grades of low-temperature seamless steel pipes

In extreme low-temperature environments, the performance of materials is crucial, especially in industries such as energy, chemical industry, shipbuilding, aerospace, and liquefied natural gas (LNG), where the performance requirements for transportation and pressure-bearing pipelines are more stringent. Low-temperature seamless steel pipes have become an important type of pipe widely used in these fields due to their excellent low-temperature toughness, stable mechanical properties, and good weldability.

This article will systematically analyze the materials and grades of low-temperature seamless steel pipes from multiple aspects such as material classification, representative grades, typical performance, application fields, and material selection recommendations, to help engineering and technical personnel make more scientific and reasonable selection decisions in practical applications.

1. Basic concepts of low-temperature seamless steel pipes
Low-temperature seamless steel pipes, as the name suggests, are seamless steel pipes specially designed for low-temperature environments. Unlike ordinary structural steel pipes, they can still maintain excellent toughness and strength under working conditions of dozens of degrees below zero or even lower temperatures, avoiding rupture or failure due to material embrittlement.

Generally, the working temperature range of low-temperature seamless steel pipes is -45°C to -196°C, and some high-end materials can even be used in extreme low temperatures of -269°C, such as ultra-low temperature medium transportation systems such as liquid hydrogen and liquid helium.

2. Main material types of low-temperature seamless steel pipes
The materials of low-temperature seamless steel pipes are mainly divided into two categories:

1. Low-temperature carbon steel
Low-temperature carbon steel is the most common low-temperature steel material, which is characterized by maintaining good toughness, strength and welding performance under low-temperature conditions. By controlling the carbon content and adding a small amount of manganese, silicon and other elements, its performance in low-temperature environments can be significantly improved.

Common representative grades:

ASTM A333 Grade 6: The most widely used low-temperature carbon steel pipe, suitable for working conditions below -45°C, with both cost-effectiveness and comprehensive performance.

ASTM A420 WPL6: Commonly used for low-temperature pipe fittings, used in conjunction with A333 Gr.6.

Performance characteristics:

Tensile strength is as high as 415 MPa

Yield strength is about 240 MPa

Impact toughness at -45°C is qualified (Charpy V-notch)

Can be welded with other steels with good welding performance

Typical applications:

LNG, LPG storage tanks and transportation pipelines

Petrochemical equipment low-temperature pipelines

Low-temperature pressure vessels and heat exchangers

2. Low-temperature alloy steel
In order to further improve low-temperature resistance and corrosion resistance, alloy elements such as nickel (Ni), chromium (Cr), and molybdenum (Mo) are introduced into steel to form low-temperature alloy steel. It can still maintain high strength and high ductility at lower temperatures and is suitable for more extreme low-temperature environments.

Common representative grades:

ASTM A333 Grade 3: Alloy steel containing 1.1% nickel, suitable for -101°C working conditions.

ASTM A333 Grade 9: Alloy steel containing 9% nickel, especially suitable for LNG working conditions (-196°C).

ASTM A334 Gr.1, Gr.6: Another alloy steel standard commonly used for low-temperature heat transfer tubes.

Performance characteristics:

Enhanced impact toughness and ductility

Excellent resistance to hydrogen embrittlement and corrosion

Applicable to cryogenic treatment equipment

Higher relative cost than carbon steel

Typical applications:

LNG cryogenic storage and transportation system

Liquid nitrogen/liquid oxygen storage tanks and pipeline systems

Aerospace, cryogenic equipment manufacturing

Hydrogen energy pipeline

III. Comparison of main standards and materials

Material grade Chemical composition characteristics Applicable temperature Features
ASTM A333 Gr.6 Low carbon + manganese -45°C Strong versatility, high cost performance, wide application
ASTM A333 Gr.3 Contains 1.1% nickel -101°C Good toughness, suitable for deeper cold environments
ASTM A333 Gr.9 Contains 9% nickel -196°C Excellent ultra-low temperature performance, used in the LNG industry
ASTM A420 WPL6 For use with matching pipe fittings -46°C Compatible with Gr.6, excellent welding performance
ASTM A334 Gr.1 Ordinary low temperature alloy -45°C Commonly used in heat exchange occasions such as boiler heat exchangers
ASTM A334 Gr.6 Nickel-manganese alloy -73°C Stronger toughness, suitable for cooling systems
IV. Analysis of key performance indicators
1. Impact toughness
The material is prone to brittle fracture in low temperature environments, so the steel pipe must pass the impact test under specific low temperature conditions (such as -45°C, -101°C or -196°C) to ensure sufficient toughness.

2. Chemical composition stability
By controlling the proportion of basic elements such as carbon, manganese, and silicon, and adding alloying elements such as nickel and chromium, the phase change stability of the material at low temperature is achieved, thereby preventing the occurrence of coarse grains or microcracks.

3. Weldability
Low-temperature seamless steel pipes are often used for engineering structure connections, and good weldability is the guarantee of engineering construction. Carbon steels such as ASTM A333 Gr.6 have excellent welding performance, while high-alloy steels require reasonable preheating and post-heat treatment to ensure joint strength.

4. Corrosion resistance
Especially in marine engineering and chemical media environments, steel pipes are required to be not only resistant to low temperatures, but also resistant to acid, alkali, salt spray and other corrosion properties. The higher the nickel content, the stronger the material's corrosion resistance.

V. Application fields and typical projects
Low-temperature seamless steel pipes are widely used in the following industries:

Energy field: liquefied natural gas (LNG), liquefied petroleum gas (LPG) transmission pipelines and cryogenic pressure vessels

Petrochemical: cryogenic gas separation equipment, cryogenic reactors

Aerospace: rocket fuel delivery system

Nuclear industry: liquid hydrogen transportation pipeline system

Shipbuilding: LNG ship internal piping and storage tanks

Food refrigeration equipment: liquid nitrogen cooling system pipelines

VI. Material selection suggestions and procurement precautions
In actual projects, the selection of suitable low-temperature seamless steel pipe materials and grades requires comprehensive consideration of the following factors:

Working temperature range: clarify the minimum working temperature and select steel grades that meet the impact toughness requirements.

Media type and corrosiveness: If acidic or hydrogen media are involved, alloy steel grades should be given priority.

Construction welding conditions: For working conditions with strict requirements for welding, grades with good welding performance should be preferred.

Economic evaluation: Under the premise of meeting the performance, reasonably weigh the material cost and choose the material with higher cost performance.

Certification and standards: Ensure that the steel pipe has international standard certification such as ASTM and ASME, and is accompanied by a low-temperature impact test report and a material inspection certificate.

VII. Conclusion
As an important material under extreme working conditions, the selection of material and grade of low-temperature seamless steel pipe plays a decisive role in the safety, reliability and service life of the project. From ordinary low-temperature carbon steel to high-performance alloy steel, the development and application of each material is the crystallization of science and technology and engineering experience.

In the future, with the development of hydrogen energy and deep cold technology, the requirements for low-temperature steel pipes will be higher. We also look forward to the emergence of more advanced materials to escort human exploration of deeper low-temperature fields.


Baowi Steel Manufacturing Co.,Ltd is a steel production enterprise integrating ironmaking, steelmaking, and rolled products. Specific products include seamless steel pipes, ERW steel pipes, SSAW steel pipes, casing and tubing, drill pipes, drill collars, pipe fittings, etc.