How to distinguish grade of seamless steel pipes?

Seamless steel pipes are widely used in petrochemical, fertilizer, machinery, and aviation industries due to their high-pressure and high-temperature resistance. They are generally classified into Grade I (high-precision tube), Grade II (standard precision tube), and Grade III (general-purpose tube). Understanding their differences is crucial for selecting the right pipe for specific applications.

Union Steel Industry Co., Ltd is professional seamless steel pipes manufacturer, for more details, please contact:sales@union-steels.com

1. Wall Thickness

Grade I Pipes: Thickest wall, typically 8-20mm, with excellent uniformity and minimal deviation. Suitable for high-pressure applications such as hydraulic systems.

Grade II Pipes: Wall thickness ranges from 5-12mm, with slightly higher deviations than Grade I pipes.

Grade III Pipes: Thinner walls, 3-10mm, with less uniformity and a higher margin of error, making them more suitable for low-demand applications.

2. Length

Grade I Pipes: Fixed lengths, typically over 12m, suitable for high-precision industrial applications.

Grade II Pipes: Standard lengths range between 6-12m.

Grade III Pipes: Shortest, between 3-6m, ideal for temporary construction or low-length requirements.

3. Precision

Grade I Pipes: Highest precision, with dimensional deviations controlled within ±0.5mm.

Grade II Pipes: Moderate precision, deviations within ±1mm.

Grade III Pipes: Lower precision, deviations within ±1.5mm.

4. Material and Chemical Composition

Grade I Pipes: Made from high-performance steels, such as 20#, 20Cr, 12CrMoV, 15CrMoG, and other alloy steels with strict composition control.

Grade II Pipes: Made from standard industrial materials, meeting GB/T, ASTM, DIN standards.

Grade III Pipes: Typically made from ordinary carbon steel or low-alloy steel, with fewer material requirements.

5. Mechanical Properties

Grade I Pipes: Highest mechanical strength, excellent tensile strength, yield strength, and elongation, ensuring durability under extreme conditions.

Grade II Pipes: Balanced mechanical properties, suitable for general industrial applications.

Grade III Pipes: Lower mechanical strength, mainly used in low-load environments with minimal pressure requirements.

Conclusion

The grade of seamless steel pipes is determined by wall thickness, length, precision, material composition, and mechanical properties. When selecting pipes, it is essential to match the grade to the specific application to ensure safety, efficiency, and durability.