Square Tubing: 20 × 20 mm to 400 × 400 mm、Rectangular Tubing: 30 × 20 mm to 500 × 300 mm
WT Range :
1.5 mm ～ 20 mm
Length :
6m、12m
Tolerance :
Outer diameter/width and height ±1%、 wall thickness ±0.2 to 0.5 mm、 length ±5 to 10 mm、 straightness ≤0.2% of length
Material :
Carbon Steel（S235JRH、S275JRH、S355J2H）
Standard :
EN 10210-1 / EN 10219-1、ASTM A500、GB/T 6728、GB/T 3094
Application :
Square and rectangular carbon steel pipes are widely used in load-bearing and supporting components for building structures, machinery manufacturing, industrial pipe racks, and decorative furniture.
I. Introduction to Square and Rectangular Carbon Steel Tubes
Square and rectangular carbon steel tubes are hollow structural steel products manufactured from hot-rolled or cold-rolled carbon structural steel strips through forming, welding, or seamless extrusion. Featuring square or rectangular cross-sections, they offer excellent load-bearing capacity, bending strength, and structural stability.
These pipes find extensive applications in building structures, machinery manufacturing, steel frameworks, solar panel supports, automotive chassis, and warehouse shelving systems. Compared to round pipes, square and rectangular tubes offer advantages in planar connections and stress distribution, facilitating welding and assembly.
Based on production methods, they are categorized into hot-rolled, cold-drawn, ERW-welded, and seamless square/rectangular tubes.
Common applicable standards include EN 10210 (hot-rolled structural), EN 10219 (cold-formed structural), ASTM A500, and GB/T 6728.
II. Comparison of Square, Rectangular, and Round Carbon Steel Pipes
Carbon steel pipes are categorized into square, rectangular, and round types based on their cross-sectional shapes. Though made of the same material, their structural forms differ, resulting in distinct characteristics regarding load-bearing capacity, connection methods, processing techniques, and application scenarios.
i. Distinction Overview
Square Tubes: Equal cross-sectional sides ensure uniform stress distribution, excellent torsional resistance, and aesthetically pleasing profiles. Ideal for framework structures and decorative projects. Rectangular Tubes: Unequal width and height provide superior bending resistance. More economical for unidirectional load-bearing structures like supports and bridge girders. Round Tubes: Deliver the most uniform stress distribution, making them particularly suitable for withstanding internal pressure or fluid conveyance, such as in oil pipelines, water supply/drainage pipes, and boiler tubes.
ii. Structural and Performance Comparison Table
Comparison Item
Square Carbon Steel Tube
Rectangular Carbon Steel Tube
Round Carbon Steel Tube
Cross-section Shape
Four equal sides
Unequal length and width
Circular cross-section
Mechanical Properties
Balanced torsion and bending resistance
Excellent bending resistance, suitable for unidirectional load
Oil & gas pipelines, water pipes, heat exchanger tubes
iii. Selection Recommendations
Pressure-bearing conveyance projects → Recommend round pipes (e.g., API 5L, ASTM A106); Building and mechanical structures → Recommend square or rectangular pipes (EN 10210 / EN 10219); Decorative applications, display racks, and lightweight structures → Prioritize cold-formed square or rectangular pipes for aesthetic appeal and dimensional accuracy.
III. Classification of Square and Rectangular Carbon Steel Pipes
i. Classification by Manufacturing Process
Type
Production Features
Applicable Scenarios
ERW Steel Tube (Electric Resistance Welded)
Formed from hot-rolled or cold-rolled strip steel via high-frequency welding; smooth weld seam, high precision, suitable for mass production
Building structures, steel frameworks, scaffolding, vehicle frames
Hot-Rolled Square & Rectangular Tube
Formed by hot rolling; larger dimensional tolerance but high strength, suitable for heavy-duty structures
1. Raw Material Preparation: Select hot-rolled or cold-rolled steel strip/coil.
2. Annealing/Pickling: Enhance material ductility and remove surface scale.
3. Shearing: Cut into strip lengths suitable for forming.
4. Forming: Shape into square or rectangular tube blanks via cold bending or hot rolling.
5. Welding: High-frequency ERW welding, or seamless tube hot rolling/cold drawing forming.
6. Weld Bead Leveling: Remove weld protrusions to ensure surface flatness.
7. Straightening: Ensure tubular material straightness.
8. Dimension Cutting: Cut to customer-specified lengths.
9. Internal/External Surface Treatment: Acid pickling, polishing, or galvanizing to enhance corrosion resistance.
10. Non-Destructive Testing: UT ultrasonic, radiographic, or eddy current testing to ensure quality.
11. Rust Prevention: Apply rust-inhibiting oil or implement other protective measures.
12. Final Inspection: Verify dimensions, mechanical properties, and visual appearance.
13. Storage & Packaging: Stack neatly, apply protective packaging, and prepare for shipment.
Inspection Item
Testing Method
Standard Requirements / Description
Significance for Procurement & Use
Chemical Composition
Optical Emission Spectroscopy (OES) / Chemical Analysis
Meet material grade requirements, e.g., S235JRH, S355J2H
Ensures welding performance and stable mechanical properties
Smooth surface, free of severe scratches, cracks, rust
Improves appearance and corrosion resistance
Square and Rectangular Carbon Steel Pipe Selection FAQ
Q1: Should square tubes or rectangular tubes be selected for building frame structures?
A1:
Square tubes: All four sides are equal in length, offering excellent torsional resistance. Suitable for columns, frame columns, and uniformly loaded structures.
Rectangular tubes: Unequal length-to-width ratio provides superior bending resistance along the longer side. Suitable for beams, cross-braces, or directionally loaded structures.
Recommendation: Select cross-sections based on load direction. Square tubes are preferred for columns, while rectangular tubes are preferred for beams or braces.
Q2: How to determine wall thickness and cross-sectional dimensions?
A2:
Calculate cross-sectional dimensions and wall thickness based on structural load-bearing capacity, span, and load type.
For general industrial and office buildings:
Square tubes: 80×80mm to 150×150mm, wall thickness 4–6mm
Rectangular tubes: 80×40mm to 150×100mm, wall thickness 4–6mm
Recommendation: Select based on design drawings and load requirements, not solely by external dimensions.
Q3: How should cold-formed tubes and hot-rolled tubes be selected for building frames?
A3:
Hot-rolled tubes: Uniform strength and good toughness, suitable for frames with heavy loads and long spans.
Cold-formed tubes: High dimensional accuracy and low cost, suitable for lightweight or non-load-bearing structures.
Recommendation: Select hot-rolled or seamless tubes for primary frame columns and beams; choose cold-formed tubes for lightweight secondary frames or decorative structures.
Q4: How can the durability of square and rectangular tubes be ensured in outdoor environments?
A4:
Recommend selecting hot-dip galvanized square/rectangular tubes or surface coating treatments for effective corrosion and rust prevention.
For critical load-bearing structures, consider periodic anti-corrosion maintenance or protective paint application.
Practical tip: When purchasing, inspect galvanization thickness or coating uniformity to ensure long-term rust resistance.
Q5: How to select pipe materials under different standards?
A5:
Common standards: EN 10210, EN 10219, ASTM A500, GB/T 6728.
EN 10210 (hot-rolled) is suitable for load-bearing structures, while EN 10219 (cold-formed) is suitable for lightweight structures.
Recommendation: Select pipes conforming to the relevant standard based on engineering design requirements to ensure load-bearing capacity and safety factors.
Q6: What precautions should be taken during installation and welding?
A6:
Ensure pipe dimensional tolerances remain within allowable ranges (OD, wall thickness, straightness).
Deburr square and rectangular tubes before welding to prevent stress concentration.
During installation, note force direction: place beam flanges facing load direction and install columns vertically.
Practical tip: Request laser diameter measurement or straightness reports from manufacturers for expedited on-site acceptance.
