Square Hollow Structural Steel Tubes

HAISHENG supplies Square Hollow Structural Steel Tubes in stock—cold-formed sections in welded and seamless types, complying with GB/T 6728 and GB/T 3094. Made from Q235B, Q355B, and 20# steel. Sizes from 20×20 to 300×300, wall thickness 1.2-40mm, standard lengths 6m/9m/12m. Features uniform four-way stiffness, flat surfaces for easy connection, and versatile processing options. Ideal for structural columns, trusses, curtain wall framing, guardrails, and equipment racks.

Product Advantages and Features

I. Structural Mechanics Characteristics

1. The hollow square cross-section ensures uniform stiffness across all four directions. It offers robust resistance to bending, torsion, and lateral loads, providing better overall structural stability than circular tubes.

2. Available in two categories: welded and seamless. Welded tubes offer strength sufficient for standard load-bearing needs, while seamless square tubes—free from weld seams and featuring a dense microstructure—offer superior fatigue resistance, pressure tolerance, and impact strength, making them ideal for heavy-duty, cyclic loading conditions.

3. Under identical load conditions, they are lighter than solid square steel bars and offer high cross-sectional efficiency, effectively reducing the overall structural load of the building.

II. Profile and Assembly Characteristics

1. Flat outer walls and precise, sharp edges ensure a tight fit with panels, trim components, and cladding elements. This simplifies splicing, edge finishing, and sealing processes.

2. They provide a clean, uniform visual appearance, combining structural load-bearing capabilities with aesthetic appeal—making them suitable for architectural features and facade framing.

3. Standardized dimensional modules ensure high interchangeability within the product series, boosting efficiency during on-site assembly and alignment.

III. Processing and Connection Characteristics

1. They can be cut, beveled, drilled, bent, and welded. They exhibit excellent cold and hot working properties, making secondary processing straightforward.

2. Various connection methods are supported; while welding is the standard approach, bolting, riveting, and flanging can also be used to suit different structural joint requirements.

3. A comprehensive range of specifications is available—from small decorative tubes to large-section load-bearing columns—offering extensive selection options. 

IV. Corrosion Resistance and Environmental Adaptability

1. Supplied in a raw "black pipe" state; can undergo anti-corrosion treatments such as hot-dip galvanizing, painting, powder coating, or epoxy coating; suitable for use in standard indoor and outdoor environments.

2. Good temperature adaptability under standard operating conditions; applicable temperature range: -20°C to 200°C.

V. Product Limitations

1. Stress concentration occurs at corners; prone to fatigue damage at these points when subjected to severe impacts or high-frequency alternating loads over long periods.

2. Cross-sectional shape limits fluid transport applications; primarily positioned as a structural material.

3. High production costs for large-specification, thick-walled seamless square tubes result in prices far higher than welded versions; welded tubes offer better cost-effectiveness for standard applications.

Uses and Scope of Application

I. Primary Uses

1. Key Load-Bearing Components for Steel Structures

Square hollow structural steel tubes serve as building columns, roof trusses, support pillars, platform frames, and floor support frameworks; widely used in the main structures of factory buildings, stadiums, warehouses, and other projects.

2. Building Envelopes and Curtain Wall Systems

External wall framing (girts), door and window frames, skylight frameworks, and wall edge structures; compatible with the installation of cladding materials such as color-coated steel sheets and panels.

3. Protective and Municipal Facilities

Road guardrails, factory perimeter fencing, stair handrails, hoarding supports, bus station structures, landscape pergolas, etc.

4. Equipment and Storage Racks

Machinery bases, equipment frames, workbench frames, heavy-duty storage racks, and container auxiliary structures.

5. Engineering and Temporary Facilities

Temporary construction supports, site hoardings, stage trusses, and greenhouse frameworks.

6. Decorative and Architectural Structures

Indoor and outdoor decorative frameworks, exhibition booth structures, and outdoor artistic installations; combining load-bearing and decorative functions.

II. Scope of Application

1. Steel Structure Engineering: Main load-bearing structures for industrial plants, prefabricated buildings, large stadiums, warehouses, etc.

2. Municipal and Transportation: Road safety barriers, municipal hoardings, landscape projects, and bus station facilities. 3. Architectural Decoration: Building curtain walls, doors and windows, interior/exterior architectural features, and commercial showrooms.

4. Machinery Manufacturing: General-purpose equipment, construction machinery, and logistics equipment frameworks.

5. Agriculture, Forestry, and Horticulture: Greenhouses, livestock shelter frames, and agricultural fencing.

6. Temporary Works: Construction site temporary supports, modular building frames, and temporary hoarding/barriers.

Selection Guide

· Welded Square Tubes: Cost-effective with ample stock availability; suitable for standard applications such as general load-bearing, enclosures, guardrails, decoration, and lightweight frameworks.

· Seamless Square Tubes: Offer superior overall strength, fatigue resistance, and impact resistance; primarily used for high-standard applications such as heavy-load columns, high-pressure structural components, and precision equipment frameworks. Key Performance Parameters

Implementation Standards

GB/T 6728-2017 "Cold-formed hollow structural sections" (Welded square tubes)

GB/T 3094-2012 "Cold-drawn seamless steel tubes for structural purposes" (Seamless square tubes)

I. Common Materials and Mechanical Properties

General Physical Parameters of Square Hollow Structural Steel Tubes

· Density: 7.85 g/cm³

· Modulus of Elasticity: 2.06 × 10⁵ MPa

· Standard Operating Temperature: -20°C to 200°C

II. Specifications and Dimensions

1. Designation Format

Side length × Wall thickness (Unit: mm); Example: 80×80×3.0

2. Main Size Categories

· Small (Decoration / Enclosure / Guardrails): 20×20 to 50×50; wall thickness 1.2–2.5 mm

· Medium (Keels / Purlins / Standard beams & columns): 60×60 to 100×100; wall thickness 2.0–5.0 mm

· Large (Load-bearing columns / Heavy-duty trusses): 120×120 to 300×300; wall thickness 4.0–14.0 mm

· Extra-thick wall: Maximum wall thickness up to 40 mm

3. Lengths and Tolerances

· Standard lengths: 6 m, 9 m, 12 m; custom lengths available

· Side length tolerance: ±0.8%

· Wall thickness tolerance: Welded tubes ±10%; Seamless tubes ±7.5%

4. Theoretical Weight Calculation Formula

W (kg/m) = 0.0314 × (D − t) × t (D = Side length, t = Wall thickness)

III. Sectional Mechanical Properties

1. Square cross-section; uniform bending and torsional rigidity in all four directions; lateral stability superior to that of round tubes.

2. Stress concentration occurs at the corners; not suitable for applications involving high-frequency impact or severe cyclic loading. 3. Processing performance of square hollow structural steel tubes: Withstands 90° cold bending at ambient temperature and flattening tests without cracking or delamination of the tube wall.

IV. Performance comparison of the two product types

V. Surface treatment and anti-corrosion

1. As-manufactured state: Black steel tube (hot-rolled oxide finish)

2. Common anti-corrosion processes: Hot-dip galvanizing, cold galvanizing, epoxy coating, electrostatic powder coating, fluorocarbon coating

3. Hot-dip galvanized coating specifications: Average thickness ≥85 μm; service life of over 15 years under normal outdoor conditions

VI. Connection methods

· Primary connections: Bevel welding, full-penetration welding

· Secondary connections: High-strength bolting, riveting, self-tapping screws

· Compatible with steel structural components such as H-beams, circular tube columns, color steel sheets, and trim elements

VII. Applicable / Non-applicable scenarios

Applicable

Steel structural columns, trusses, curtain wall framing, enclosure frameworks, municipal guardrails, equipment racks, landscape structures, and prefabricated buildings.

Not applicable

High-pressure fluid transport, high-temperature and high-pressure piping, pipelines conveying highly corrosive media, and core components subject to severe, repeated impact.

FAQ

Q1: What is the difference between welded and seamless square tubes?

A: Welded square tubes are formed by cold-bending steel strip and longitudinally welding the seam. They offer high cost-performance, complete specifications, and fast delivery—ideal for general load-bearing components, enclosures, and curtain wall framing. Seamless square tubes are cold-drawn or extruded without a weld seam, offering superior strength, fatigue resistance, and pressure-bearing capacity—ideal for heavy-load columns, precision equipment frames, and high-pressure structural components.

Q2: How to choose between Square Hollow Structural Steel Tubes and round tube for columns?

A: Square tubes offer flat surfaces for easy connection to beams and cladding panels, making them ideal for structural frames and enclosures. Round tubes offer uniform stiffness in all directions and lower wind resistance, making them ideal for exposed columns, landscape structures, and high-wind areas. For standard industrial building columns, square tubes are often the more practical choice.

Q3: What are the standard sizes available for square tubes?

A: HAISHENG stocks sizes from 20×20 (small, for decoration and guardrails) to 300×300 (large, for heavy-duty columns). Wall thickness ranges from 1.2mm to 40mm. Standard lengths are 6m, 9m, and 12m. Custom sizes and lengths are available upon request.

Q4: What is the recommended anti-corrosion treatment for outdoor use?

A: For outdoor and coastal environments, hot-dip galvanizing is recommended (zinc coating ≥85μm, service life >15 years). For indoor or light outdoor use, painting, powder coating, or epoxy coating is sufficient. All surface treatments can be applied after cutting, drilling, and welding.

Q5: Can square tubes be used as primary load-bearing columns?

A: Yes. Square tubes are widely used as primary columns in steel structures. Their closed square cross-section offers uniform stiffness in all directions, making them suitable for medium-to-heavy load columns in industrial plants, warehouses, and prefabricated buildings. For ultra-heavy loads or high-rise buildings, concrete-filled square tubes or H-beams may be more appropriate.