Carbon steel square tube (also called square hollow section, SHS, or square structural tubing) is one of the most widely used structural products for steel buildings, machinery frames, fencing, and architectural fabrications. The shape provides excellent torsional resistance, four flat surfaces for welding and bolting, and an aesthetic appearance for exposed structural applications.
Huaxia-Steel supplies carbon steel square tube in cold-formed (ERW welded) and hot-formed (structural) conditions, in mild steel (ASTM A500 Grade B / C), carbon steel (SS400, Q235, Q355), and high-strength structural grades (ASTM A500 Grade C, EN 10025 S355J2H, GB Q355). Available in sizes from 20 × 20 mm to 500 × 500 mm square, with wall thicknesses from 1.0 mm to 25 mm.
Product Overview
Square hollow sections are categorized by their manufacturing process:
- ERW (Electric Resistance Welded) cold-formed: Most common for thin walls (1 – 12 mm) and small-to-medium sizes. Formed from cold-rolled or hot-rolled strip and welded along a single seam.
- Hot-formed seamless or expanded: Used for thicker walls (≥10 mm) and larger sizes. Often normalized after forming for improved toughness.
- Structural hollow sections (SHS): Per EN 10210 (hot-formed) or EN 10219 (cold-formed), used in building and civil engineering.
Specifications
Standards & Grade
- ASTM A500 Grade B / C: Standard specification for cold-formed welded and seamless carbon steel structural tubing in rounds and shapes
- ASTM A501: Hot-formed welded and seamless carbon steel structural tubing
- EN 10210: Hot-finished structural hollow sections (S355J2H, S275J0H)
- EN 10219: Cold-formed welded structural hollow sections (S235JRH, S275J0H, S355J2H)
- JIS G3466: Carbon steel square tubes for general structural purposes (STKR400, STKR490)
- GB/T 6728: Cold-formed hollow steel sections (Q235, Q355)
- GB/T 8162: Seamless steel tubes for structural purposes
Dimensional Range
| Parameter | Range |
|---|---|
| Side length (A × A) | 20 × 20 mm – 500 × 500 mm (smaller sizes more common in ERW) |
| Wall thickness (t) | 1.0 mm – 25 mm |
| Standard length | 6 m / 12 m (cut-to-length available) |
| Length tolerance | +50 mm / -0 mm typical |
| Square-of-squares dimension tolerance | ±1% of side length (typically ±1 – 2 mm) |
| Wall thickness tolerance | ±10% (per A500) or ±7.5% (per EN 10219) |
| Straightness | 1 mm per meter, max 0.2% of length |
Mechanical Properties by Grade
| Grade / Standard | Yield (MPa, min) | Tensile (MPa, min) | Elong (%) |
|---|---|---|---|
| ASTM A500 Grade B | 290 (≤25 mm wall) | 430 | 23 |
| ASTM A500 Grade C | 345 (≤25 mm wall) | 425 | 21 |
| ASTM A501 | 250 (≤25 mm) | 400 | 23 |
| EN 10210 S355J2H | 355 (≤16 mm) | 490 – 630 | 22 |
| EN 10219 S235JRH | 235 | 360 – 510 | 24 |
| JIS STKR400 | 245 | 400 | 23 |
| JIS STKR490 | 325 | 490 | 23 |
| GB Q235 | 235 | 375 – 500 | 26 |
| GB Q355 | 345 | 470 – 630 | 22 |
Weight Reference (selected sizes)
| Size (A × A × t, mm) | Linear weight (kg/m) |
|---|---|
| 20 × 20 × 2.0 | 1.12 |
| 40 × 40 × 2.5 | 2.92 |
| 50 × 50 × 3.0 | 4.39 |
| 75 × 75 × 4.0 | 9.03 |
| 100 × 100 × 5.0 | 14.7 |
| 150 × 150 × 6.0 | 27.4 |
| 200 × 200 × 8.0 | 48.0 |
| 300 × 300 × 10.0 | 90.2 |
| 400 × 400 × 12.0 | 144.5 |
Subgrades and Variants
| Subgrade | Use |
|---|---|
| A500 Gr.B (default) | General structural applications |
| A500 Gr.C | Higher yield for heavily-loaded structural members |
| A500 Gr.B with Charpy 27J @ 0°C | Cold-region or fatigue-loaded structures |
| EN 10219 S235JRH / S275J0H / S355J2H | European structural standards |
| Hot-formed (EN 10210 S355J2H) | Thicker walls, normalized, better for dynamic loads |
| Galvanized SHS | For outdoor / atmospheric corrosion resistance |
| Pre-painted (powder coat) | Architectural / exposed applications |
Manufacturing Standards
- ASTM A500 / A500M-21: Cold-formed welded and seamless structural tubing (rounds and shapes)
- ASTM A501: Hot-formed welded and seamless structural tubing
- EN 10210-1/-2: Hot-finished structural hollow sections of non-alloy and fine grain steels
- EN 10219-1/-2: Cold-formed welded structural hollow sections
- JIS G3466: Carbon steel square pipes for general structural purposes
- GB/T 6728: Cold-formed hollow steel sections for general structure
- EN 10204 3.1: Mill test certificate supplied with every shipment
Typical Applications
Construction & Architecture
- Steel building columns, beams, and trusses
- Steel space frames and roof structures
- Atrium and skylight structures
- Staircase stringers and handrails
- Pavilion and canopy frames
Industrial & Equipment
- Machine frames and guards
- Conveyor support structures
- Storage rack uprights, cross braces, and beams
- Pallet rack end frames
- Workbench and workstation frames
Agricultural & Outdoor
- Greenhouse structural frames (galvanized or pre-painted)
- Animal confinement and pen structures
- Fencing posts and rails
- Solar panel mounting frames
- Playground and sports equipment frames
Transport & Logistics
- Trailer frames and chassis
- Container chassis and tie-down rails
- Railcar structural members (lower strength applications)
- Modular container buildings
Welding and Fabrication
Carbon steel square tube is readily welded by:
- SMAW: E6013, E7018
- GMAW: ER70S-6 for thin walls (≤3 mm); ER70S-G for thicker
- FCAW: E71T-1 for high-deposition welding
- GTAW (TIG): ER70S-2 for precision joints
For thin walls (≤2 mm), reduce heat input to avoid burn-through. For thicker walls (≥6 mm), use low-hydrogen consumables to avoid HAZ cracking. Tube-to-tube joints are typically fillet welded on both sides for full-strength connections.
Quality Assurance
- MTC EN 10204 3.1: Per heat, with chemistry and mechanical results.
- Hydrostatic test: Standard for hydrostatic applications (A500 Gr.B/C).
- Flattening test: Verifies weld integrity for A500 product.
- Dimensional inspection: Side length, wall thickness, straightness, squareness on sampled batches.
- Surface inspection: Visual on 100% of pieces; mill scale intact (or shot-blasted if specified).
- Third-party inspection: SGS / BV / TUV / Intertek on request.
Packaging & Shipping
- Bundle packaging: Hexagonal bundles of 500 – 2,000 kg, secured with 4 – 6 steel bands
- End protection: Plastic caps or paper to keep interior clean
- Surface protection: Optional hot-dip galvanizing per ASTM A123 / ISO 1461, or pre-painted per buyer spec
- Container loading: 20′ GP for lengths ≤6 m; 40′ GP / flat-rack for lengths up to 12 m
- Lead time: Stock sizes 2 – 4 weeks; custom sizes 4 – 8 weeks
Square Tube vs Round Tube vs Rectangular Tube
Square hollow section (SHS), round hollow section (RHS), and rectangular hollow section (RHS) are the three structural tube shapes. They are not interchangeable for all applications:
| Shape | Torsional Resistance | Bending About Strong Axis | Best Aesthetic | Weld Joint Simplicity |
|---|---|---|---|---|
| Square (SHS) | Highest (uniform about both axes) | Comparable to RHS | Modern architectural | Easy: flat-to-flat connections |
| Rectangular (RHS) | Intermediate (asymmetric about axes) | Highest for one axis | Directional framings (door frames) | Easy: flat-to-flat |
| Round (CHS) | Uniform | Lower than SHS for same weight | Industrial / pipeline | Curved-to-flat connections require special fit-up |
For applications where torsion is significant (cantilevered loading, off-axis vibration), square tube outperforms both round and rectangular. For directional loading in one plane (e.g., beam bending), rectangular tube can deliver higher section modulus per kg. Round tube is preferred for fluid transport, pressure systems, or where connections are based on curved geometry.
Cost Reference for Carbon Steel Square Tube
Square tube pricing is influenced by:
- Base steel price: Trends with global hot-rolled coil; ranges $400 – $800/t equivalent over a typical annual cycle.
- Form premium: ERW tube making adds 8 – 15% over parent coil cost.
- Size premium: Common sizes (50×50, 100×100, 150×150) are stocked and cheapest; custom sizes add 10 – 30%.
- Wall premium: Thick walls (>6 mm) cost more per metre due to higher material weight per piece, but the per-tonne price may be slightly lower.
- Surface treatment: Hot-dip galvanizing adds 15 – 25% by weight equivalent (but is priced per ton).
- Length premium: 12 m lengths cost more to handle (special shipping) but save splicing cost.
For stocking decisions, focus on the 3 – 5 most-requested sizes (e.g., 50×50×3, 75×75×4, 100×100×5, 150×150×6) — these cover 70 – 80% of typical industrial demand. Custom sizes ordered 1 – 2 per shipment should be on a mill-direct basis with longer lead time.
ERW Tube Manufacturing Process
ERW (Electric Resistance Welded) is the dominant process for carbon steel square tube in the size range 20 – 200 mm and wall thickness 1.0 – 12 mm. The process:
- Coil loading: Hot-rolled or cold-rolled coil of slit width matching the perimeter of the finished tube.
- Uncoiling and forming: Strip is fed through a series of roller stands that progressively shape it from flat to round.
- HF welding: High-frequency (300 – 400 kHz) current is induced in the strip edges, raising them to welding temperature (1,300 – 1,500 °C) at the squeeze point.
- Squeeze and seam cooling: Roller pairs bring the heated edges together under pressure to form a forge weld. The seam cools rapidly in an air or water bath.
- Size reduction: The round tube passes through sizing rollers to achieve exact OD and roundness.
- Cut-off: Flying saw cuts the tube to specified length.
- Sizing to square: For SHS, the round tube passes through additional forming rolls that shape it into square or rectangular section.
- Cooling bed: Tubes cool in straight alignment under controlled conditions.
Post-weld heat treatment is often applied to normalize the HAZ microstructure and improve toughness — particularly for grades meeting Charpy requirements at low temperature.
Order Information
- Standard and grade: ASTM A500 Gr.B / C, EN 10219 S355J2H, GB Q235 / Q355, or JIS STKR400 / STKR490
- Size: Side length × side length × wall thickness (mm)
- Length: Standard 6 m / 12 m, or cut-to-length
- Surface condition: Mill, shot-blasted, oiled, hot-dip galvanized, pre-painted
- Tolerances: Per standard or tighter per agreement
- Inspection: MTC only, third-party, supplementary Charpy if required
- Delivery: FOB / CIF / DDP to port or site
Get a Quote
Need carbon steel square tube (SHS) for structural or fabrication applications? Huaxia-Steel supplies SHS in sizes 20 × 20 mm to 500 × 500 mm, with ASTM A500 Gr.B/C, EN 10219, EN 10210, JIS G3466, or GB/T 6728 compliance. Available in hot-dip galvanized, oiled, or pre-painted finishes. EN 10204 3.1 mill certificate, third-party inspection on request, global shipping. Send your spec to [email protected] for a quotation.
