ERW Square & Rectangular Tube

What is ERW square and rectangular tube?

Welded ERW square tubes and ERW rectangular tubes are steel tubes with square or rectangular cross-sections produced using the high-frequency electric resistance welding (ERW) process.

The name itself is self-explanatory:

ERW refers to the production process—high-frequency electric resistance welding.
"Square and rectangular tube" is often used as a general term, with "square tube" referring to a square cross-section and "rectangular tube" referring to a rectangular cross-section.

ERW square and rectangular tube manufacturing process:

The coiled steel strip (steel sheet) passes through a series of forming rollers, which gradually bend the straight strip into a nearly circular tube. High-frequency current creates the skin effect and proximity effect, instantly heating the tube edges to a molten state. Then, squeeze rollers press-weld and fuse the tube.

A scraper removes excess metal (burrs) extruded from the inside and outside of the weld. The ERW welded tube enters a cooling section and passes through a sizing mill to ensure precise diameter and roundness. Finally, it passes through a set of specialized dies and is gradually rolled into the desired square or rectangular cross-section. This process requires precise control to ensure the straightness of angles and edges.

Features of ERW Square and Rectangular Tubes:

1. High Efficiency and Low Cost
The ERW production process is continuous, resulting in extremely high production speeds, far exceeding those of seamless steel pipes. This results in high production efficiency and relatively low costs.

2. High Weld Quality
High-frequency welding results in a narrow heat-affected zone, fine-grained welds, high welding speeds, and minimal oxidation. This results in high weld strength, sometimes even approaching or exceeding the strength of the parent material.

3. High Dimensional Accuracy and a Smooth Surface

ERW square tubes are manufactured from cold-rolled strip steel. Their outer diameter and wall thickness are precisely controlled with tight tolerances. Their surface is free of defects such as scratches commonly found in seamless steel pipes, resulting in a smoother and more aesthetically pleasing appearance.

Key Features of ERW Rectangular Tubing:

1. Excellent Cross-Sectional Properties
A rectangular cross-section has different moments of inertia along its two principal axes, meaning it has varying bending resistance in different directions. This characteristic is very useful in structural design, allowing engineers to select the optimal installation method based on the direction of force, achieving efficient material utilization and saving steel.

2. High Strength and Good Bending and Torsional Resistance
As a closed tubular section, it has a significantly greater section modulus and bending and torsional stiffness than open sections such as angles and channels of the same weight, resulting in greater stability and improved load-bearing performance.

ERW Square Tube Specification Range:

ERW square tubes come in a wide range of side lengths, covering applications from small precision instruments to large building structures.

Common Square Tube Size Range:
Length: 20 mm × 20 mm to 500 mm × 500 mm.
Wall Thickness: 0.8 mm to 16 mm.

More detailed classifications:
Small tubes: Side length ≤ 80 mm. Commonly used in furniture, decorations, small brackets, etc.
Medium tubes: Side lengths between 80 mm and 200 mm. This is the most widely used range, used in mechanical structures, building trusses, agricultural greenhouses, etc.
Large tubes: Side lengths between 200 mm and 500 mm and above. Primarily used in large building structures (such as main beams and columns in stadiums, airports, and factory buildings), bridges, heavy machinery, etc.

Thin-wall tubes: Wall thickness is typically ≤ 3.0 mm. Mostly used in applications requiring light weight and low load-bearing capacity, such as decorations, furniture, and display racks.
Conventional-wall tubes: Wall thicknesses between 3.0 mm and 8.0 mm. This is the most popular range for structural applications, offering good strength and weight balance.
Thick-wall tubes: Wall thickness > 8.0 mm. Used in critical structural parts bearing heavy loads and high pressures.

Note: In addition to square tubes, the same production process also produces rectangular tubes, whose dimensions are expressed as length × width, for example, 100mm × 50mm.

ERW Rectangular Tube Specification Range:

1. Cross-sectional Size Range (H × B)
Rectangular tube dimensions are highly flexible, with aspect ratios (H/B) ranging from nearly 1 (almost square) to significantly larger.

Common Long Width (H) Range: 20 mm to 600 mm or even larger
Common Short Width (B) Range: 10 mm to 400 mm

Common Wall Thickness (t): 0.8 mm to 16.0 mm

Lengths: Typically 6 or 12 meters, but custom lengths are also available.
Surface Treatment: Black tube (untreated, with scale), galvanized (commonly used for rust prevention), painted, etc.

Common Length-to-Width Ratios (H/B): Typically up to 4:1 or 5:1. For example, a 400mm × 100mm rectangular tube is one of the most common extreme specifications. More extreme ratios (such as 500mm × 50mm) pose significant challenges in production and material strength and are therefore less common.

More detailed classifications:

Small rectangular tubes: H ≤ 80 mm. Commonly used in furniture, decoration, small brackets, etc.
Medium rectangular tubes: H between 80 mm and 200 mm. This is the most widely used range and is used in mechanical structures, building trusses, agricultural greenhouses, etc.
Large rectangular tubes: H > 200 mm. Primarily used in main beams and columns of large building structures, bridges, heavy machinery, etc.

Thin-wall tubes: t ≤ 3.0 mm. Mainly used in low-load applications such as decoration, furniture, and display racks.
Regular thick-wall tubes: t between 3.0 mm and 8.0 mm. This is the most popular range for structural applications, offering excellent strength and weight balance.
Thick-walled pipe: t > 8.0 mm. Used in critical structural areas subject to heavy loads and high pressures.

Common Standards:
ASTM A500: Primarily used in American standard projects, it is the commonly used structural tube standard in North America.
EN 10219: Applicable to European standard projects.
GB/T 6728-2017: Applicable to Chinese standard projects.
JIS G 3466: Applicable to Japanese standard projects.

Differences from Seamless Steel Pipe:
Seamless steel pipe: Has no welds and is made by perforating round steel. Theoretically, it has better pressure uniformity and is suitable for higher pressure applications, but it also comes at a higher cost.
ERW welded pipe: Has a longitudinal weld seam. In most structural and low- to medium-pressure fluid transportation applications, its performance is fully sufficient to replace seamless steel pipe, offering an outstanding price-performance ratio.

Applications of ERW Square & Rectangular Tube:

Due to its excellent performance and cost advantages, ERW square tube is widely used in the following areas.

1. Building Structures: Steel trusses, columns, and beams are used in factories, high-rise buildings, stadiums, bridges, and other structures, making it a primary material for modern steel structures.
2. Machinery Manufacturing: Used in the manufacture of frames, brackets, bases, and guide rails for various types of machinery and equipment.
3. Automotive Industry: Used in the manufacture of structural components such as chassis frames, bumpers, and drive shafts.
4. Agricultural Greenhouses: Serving as the framework for greenhouses, it offers high strength and corrosion resistance (typically requiring galvanizing).
5. Furniture Decoration: Used in the manufacture of modern tables, chairs, bed frames, and display racks, owing to its aesthetic appeal and strength.
6. Logistics and Warehousing: Used in the manufacture of shelves, storage cages, and logistics conveying equipment.

Conclusion:

ERW square tubes, due to their high efficiency, cost-effectiveness, high dimensional accuracy, and excellent weld quality, have become an indispensable material in numerous fields, particularly the construction and machinery industries. They are a highly effective alternative to seamless steel pipes in many low- and medium-pressure applications.

Read more: ASTM A500 Square Tube or Galvanized Square & Rectangular Tube