Square & Rectangular Tubes

Square & Rectangular Tubes, also known as square and rectangular cold-formed hollow steel sections, refer to steel pipes with square and rectangular cross-sections made by uncoiling, flattening, rolling, and welding steel strips into round tubes, and then roll-forming (or directly forming square) them.

The core advantages of square and rectangular tubes are reflected in the following aspects:
1. Reasonable cross-sectional shape: Square and rectangular cross-sections have excellent mechanical properties in terms of bending and torsion resistance, and high load-bearing capacity.
2. Lightweight and steel-saving: Under the same load-bearing conditions, square and rectangular tube structures can save 15% to 30% of steel compared to traditional I-beams and channel steel.
3. Aesthetically pleasing and easy to connect: The smooth surface of square and rectangular tubes facilitates welding, bolting connections, and decorative treatments.
4. Rich variety and specifications: Covering a wide range of specifications from micro to extra-large, meeting diverse needs.

Square & rectangular tubes can be classified in various ways, including by production process, material, cross-sectional shape, and surface treatment.

1. Classification by Production Process
Square and rectangular tubes are mainly classified into two categories according to their production process: welded square and rectangular tubes and seamless square and rectangular tubes:
(1) Welded Square and Rectangular Tubes
Welded square and rectangular tubes are made from hot-rolled or cold-rolled strip steel as raw material, which is cold-bent and then welded. According to the welding process, they can be further subdivided into:
High-Frequency Resistance Welded Square Tubes (ERW): Welding is performed using the skin effect of high-frequency current, which is the most important process for welded square and rectangular tubes.
Straight Seam Welded Square Tubes: The weld seam is parallel to the longitudinal direction of the tube body.
Spiral Welded Square Tubes: The weld seam is distributed in a spiral shape.
(2) Seamless Square and Rectangular Tubes
Seamless square and rectangular tubes are made from seamless steel pipes as raw material, through cold drawing or extrusion processes. They have a smooth surface and no weld seams. Product materials can include Q235, Q345 (16Mn), 20#, alloy steel, stainless steel, etc. 

2. Classification by Material: Square and rectangular tubes can be classified into two main categories based on their material: plain carbon steel square tubes and low alloy steel square tubes.
Plain Carbon Steel Square Tubes: Q195, Q215, Q235, SS400, 20# steel, 45# steel, etc.
Low Alloy Steel Square Tubes: Q345 (16Mn), Q390, ST52-3, etc.

3. Classification by Cross-sectional Shape:
Square Tubes: The cross-section is square.
Rectangular Tubes: The cross-section is rectangular.

4. Classification by Surface Treatment: Square tubes can be classified by surface treatment into hot-dip galvanized square tubes, electro-galvanized square tubes, oiled square tubes, pickled square tubes, etc.

5. Classification by Application: Square tubes can be classified by application into structural square tubes, decorative square tubes, building square tubes, mechanical square tubes, etc.

Surface treatment methods

Core Performance Characteristics
1. Excellent Mechanical Properties: The square and rectangular tubes have a reasonable cross-sectional shape, possessing high bending and torsional stiffness. Under the same cross-sectional area conditions, the load-bearing capacity of square and rectangular tubes is superior to that of round tubes and open-section steel.
2. Good Machining Performance: Square and rectangular tubes support various processing methods such as cutting, welding, bending, and drilling, facilitating the fabrication of various structural components and connection nodes.
3. Lightweight and Steel-Saving: Under the same load-bearing conditions, square and rectangular tube structures can save 15% to 30% of steel compared to traditional steel sections, effectively reducing project costs.
4. High Dimensional Accuracy: Cold-formed square and rectangular tubes have high dimensional accuracy and regular shape, facilitating standardized production and on-site installation.
5. Good Surface Quality: Cold-formed square and rectangular tubes have a smooth surface, free of iron oxide scale, facilitating painting and decorative treatments.

Square and rectangular tubes, characterized by their rational cross-sectional shape, high strength, and light weight, are widely used in building steel structures, machinery manufacturing, the automotive industry, containers, photovoltaic supports, and other fields. Galvanized square and rectangular tubes are divided into two categories: hot-dip galvanized (excellent corrosion resistance) and cold-dip galvanized (low cost, thin coating). Currently, square and rectangular tubes are rapidly developing towards higher strength, larger diameter and thicker walls, and innovative manufacturing processes.

According to the classification of the wall thickness of square rectangular tubes, the standards that can be implemented are:
Chinese standard:
GB/T 3094-2012 "Cold-drawn special-shaped steel pipe", GB/T 6728-2017 "Cold-formed hollow steel for structure"

British Standard:
EN10219-1-2006 "Non-alloy and fine-grained cold-formed welded hollow structural profiles"

American standard:
ASTM A500 "Welded Rectangular Tubes and Seamless Rectangular Tubes of Circular Sections and Special-Shaped Sections in Cold-Formed Carbon Steel for Structural Use"

Japanese standard:
JIS G 3466 "Corner Rectangular Pipes for General Construction"

This standard specifies the size, shape, weight and allowable deviation range of cold-formed hollow steel for structural use.

 The allowable deviation of the wall thickness of square & rectangular tubes shall not exceed plus or minus 10% of the nominal wall thickness when the wall thickness is not greater than 10mm, and plus or minus 8% of the wall thickness when the wall thickness is greater than 10mm except for wall thickness.

The usual delivery length of square & rectangular tubes is 4000mm-12000mm, mostly 6000mm and 12000mm. Square & rectangular tubes are allowed to deliver short-length and non-cut-to-length products not less than 2000mm, and can also be delivered in the form of mouthpieces, but the buyer should cut off the mouthpieces when using them. The weight of short-length and non-cut-to-length products shall not exceed 5% of the total delivery volume, and the weight of square and rectangular pipes with a theoretical weight greater than 20kg/m shall not exceed 10% of the total delivery volume.

The bending degree of the square tube shall not be greater than 2mm per meter, and the total bending degree shall not be greater than 0.2% of the total length.

The allowable deviation of the square tube size refers to the difference between the actual size and the design size of the square tube during the production and manufacturing process. This deviation can be controlled and limited by standards. According to national standards, the allowable deviations of square tube dimensions are divided into three levels, namely level A, level B and level C. Among them, level A has the smallest allowable deviation, and level C has the largest allowable deviation.
For grade A size deviation, the maximum allowable deviation is plus or minus 1mm, which is suitable for occasions with high size requirements; the maximum allowable deviation for grade B size deviation is plus or minus 1.5mm, which is suitable for occasions with general size requirements: C The maximum allowable deviation of grade dimensional deviation is plus or minus 2.0mm, which is suitable for occasions with lower size requirements.
It should be noted that when using square tubes, different allowable deviation levels should be selected according to actual conditions and usage requirements, and checked and confirmed before use. At the same time, quality control should also be strengthened during the manufacturing process to minimize the occurrence of dimensional deviations.

Common parameters for square and rectangular tubes include:
External dimensions (width × height): e.g., 50 × 50 mm, 40 × 60 mm
Wall thickness range: 1.2 mm to 10 mm
Standard lengths: 5.8m, 6m, 11.8m, or custom lengths available upon request.

Commonly used steel materials:
Q195 / Q235 / Q345
ASTM A500 Gr. B / C
EN 10219 S235 / S355