Classification and Applications of Square Steel Pipes

Square steel pipe, also known as square tube or square tubing, is a type of steel pipe with a square cross-section and equal side lengths.

Square steel pipe is a general term for square-shaped tubing, mainly made from strip steel through unpacking, leveling, rolling, and welding to form a round tube, which is then rolled into a square tube and cut to the required length. In the industrial field, “square tubing” is a common alternative name.

Classification and Manufacturing Process of Square Steel Pipes:

Square steel pipes are mainly divided into two categories:

1. Welded Square Tubes: Using strip steel as raw material, they are unpacked, leveled, rolled, and welded into a round tube, which is then rolled into a square tube. Continuous rolling technology for this type of pipe has matured since the early 20th century.

2. Seamless Square Tubes: Seamless round tubes are formed by extrusion or through hot rolling, cold drawing, and other processes. In recent years, hot expansion technology has made new progress. For example, the patented technology of “hot expansion mandrel for round-to-square steel pipes” that appeared in 2025 enables the one-time hot expansion of a round tube into a seamless square tube.

Performance Indicators of Square Steel Pipes:

The mechanical properties of square steel pipes are mainly measured by the following indicators:

* Strength: The ability to resist damage, with tensile strength as the basic indicator.

* Plasticity: The ability of a material to undergo permanent deformation under load without breaking.

* Hardness: A measure of the hardness of a material, commonly measured using methods such as Brinell hardness (HB), Rockwell hardness (HRA/HRB/HRC), and Vickers hardness (HV).

* Impact Toughness: The ability to resist damage from impact loads.

* Fatigue Performance: The durability under cyclic loading.

Specifications and Materials of Square Steel Pipes:

* Common Specifications: Side lengths range from 20×20mm to 500×500mm, and wall thicknesses range from 2mm to 25mm. Customization is available upon request.

* Common Materials: Thin-walled pipes often use a mixture of Q195-Q215 materials, while thick-walled pipes commonly use Q235 carbon structural steel. High-strength materials such as Q345B usually require customization.

* Length: Common standard lengths on the market are 6 meters or 12 meters.

Applications of Square Steel Tubes: Square steel tubes have a wide range of applications, including:

* Construction: Steel structure engineering, curtain wall decoration, building framing.

* Industrial Manufacturing: Machinery manufacturing, automobile chassis, boiler construction, pressure vessels.

* Infrastructure: Bridges, airports, power engineering, solar power generation supports.

* Others: Shipbuilding, shelving welding, daily necessities components, etc.

Main International Standards for Square Steel Tubes:

– American Standard: ASTM A500

Applicable to cold-bent welded and seamless carbon steel structural tubing, including square, rectangular, and circular sections. This standard specifies chemical composition, mechanical properties, dimensional tolerances, and inspection requirements.

– European Standards: EN 10219 (Cold-formed welded hollow profiles) and EN 10210 (Hot-rolled seamless hollow profiles)

– EN 10219 applies to cold-formed welded square/rectangular tubes;

– EN 10210 applies to hot-rolled seamless square/rectangular tubes;

Both cover material grades such as S235 and S355, and specify dimensions, tolerances, mechanical properties, and test methods.

– Japanese Standard: JIS G 3466

Specifies the technical conditions for cold-formed carbon steel structural square and rectangular tubes, including materials (e.g., SS400, STK490), dimensional ranges, and performance requirements.

– Australian Standard: AS 1163

Applies to cold-formed hollow profiles for carbon steel and low-alloy steel structures, including square and rectangular sections.

Other Relevant International Standards

– ISO 65:1996: Applicable to dimensions and tolerances of seamless steel tubes, partially applicable to square steel tubes (reference). – ISO 3183:2019: Primarily used for steel pipes for oil and gas transportation. While mainly round pipes, supplementary requirements may be required for shaped pipes (such as square pipes) in special projects.

Domestic Standards Alignment with International Standards

The commonly used Chinese standards for square steel pipes, GB/T 6728 and GB/T 3094, are largely harmonized with the aforementioned international standards (such as EN and ASTM), especially in the area of ​​cold-formed hollow structural steel sections. For example:

– GB/T 6728-2017 corresponds to EN 10219 and ASTM A500;

– GB/T 3094-2012 corresponds to cold-drawn seamless square pipes, with some overlap with ISO standards.

In summary, the main international standards for square steel pipes are ASTM A500 (USA), EN 10219/EN 10210 (Europe), JIS G 3466 (Japan) and AS 1163 (Australia). The specific selection should be based on the project location, design specifications and material requirements.