Pre-galvanized carbon steel square tube (also called galvanized SHS — Structural Hollow Section — or “squat tube”) is the workhorse of low-rise construction, fencing, light structural framing, and OEM fabrication. It carries zinc on the outside and a clean weldable substrate underneath, so it cuts, welds, and threads cleanly while resisting corrosion in service. Huaxia-Steel ships hot-dip galvanized and pre-galvanized square tube directly from rolling mill to your port, with mill-direct pricing, dual-certified standard coverage, and the documentation chain your QA team expects.
Product Overview
Galvanized square tube is made by forming hot-rolled or cold-rolled carbon steel strip into a square section, then continuously welding the seam and — for hot-dip galvanized tube — passing the welded section through a molten zinc bath. The pre-galvanized route uses a zinc-coated coil fed directly into the forming line, which keeps the surface smoother and the cost lower than the post-weld hot-dip route for many applications. Both finishes adhere to the same zinc-coating mass classes (Z120, Z180, Z275, etc.).
Common applications include:
- Fence posts and railing frames (residential, commercial, agricultural).
- Light structural framing for carports, greenhouses, and warehouses.
- Solar panel mounting structures, especially utility-scale ground-mount.
- Furniture manufacturing — outdoor seating, school desks, retail fixtures.
- Mechanical OEM parts where mild corrosion resistance is required.
- Architectural accents, balustrades, handrails.
- Cable tray and conduit support.
- Agricultural equipment, greenhouse frames, livestock enclosures.
Specifications
| Attribute | Typical Range |
|---|---|
| Section shape | Square hollow section (SHS), seamless-look welded seam |
| Side dimension (A) | 20 x 20 mm to 200 x 200 mm (with intermediate sizes on request) |
| Wall thickness (T) | 1.0 mm to 6.0 mm (standard); up to 12 mm for heavy structural |
| Length | 6 m standard; 4 m, 9 m, 12 m on request; custom cut-to-length |
| Steel grade | Q195, Q235, Q345, SS400, ASTM A500 Grade B/C, EN 10219 S235JRH/S275JRH, GB/T 6728 |
| Zinc coating mass | Z120 (120 g/m2), Z180 (180 g/m2), Z275 (275 g/m2); heavy Z350 / Z600 by agreement |
| Galvanizing route | Pre-galvanized (coil-fed) or hot-dip galvanized (post-weld); both available |
| Surface finish | Spangled, minimized-spangle, or zero-spangle skin-passed; oiled or chromate-passivated |
| Surface treatment (optional) | RoHS-compliant trivalent passivation (Cr-free); clear or colored anti-fingerprint |
| Mill test certificate | EN 10204 3.1 mill cert; 3.2 with independent witness on request |
| Tolerance (dimension) | +/- 0.5 mm on side dimension; +/- 6 % on wall for thin wall; +/- 5 % on length |
| Straightness | 1.5 mm/m or better |
| Bundle packaging | Hexagonal bundles, plastic sleeve, steel strapping; 4-7 mm corner protection; container-fit bundle count |
Available Sizes and Stock
The table below captures our ex-stock size range for pre-galvanized square tube. Other sizes and custom lengths roll-mill-direct in 3-5 weeks.
| Sizes A x A (mm) | Walls (mm) | Length | Stock Status |
|---|---|---|---|
| 20 x 20 | 1.0, 1.2, 1.5, 2.0 | 6 m | Ex-stock |
| 25 x 25 | 1.2, 1.5, 2.0, 2.5 | 6 m | Ex-stock |
| 30 x 30 | 1.2, 1.5, 2.0, 2.5, 3.0 | 6 m | Ex-stock |
| 40 x 40 | 1.2, 1.5, 2.0, 2.5, 3.0, 4.0 | 6 m | Ex-stock |
| 50 x 50 | 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 | 6 m / 12 m | Ex-stock |
| 60 x 60 | 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 | 6 m / 12 m | Ex-stock |
| 75 x 75 | 2.0, 2.5, 3.0, 4.0, 5.0 | 6 m / 12 m | Mill-direct |
| 80 x 80 | 2.0, 2.5, 3.0, 4.0, 5.0, 6.0 | 6 m / 12 m | Ex-stock |
| 100 x 100 | 2.0, 2.5, 3.0, 4.0, 5.0, 6.0 | 6 m / 12 m | Ex-stock |
| 120 x 120 | 3.0, 4.0, 5.0, 6.0 | 12 m | Mill-direct |
| 140 x 140 | 3.0, 4.0, 5.0, 6.0 | 12 m | Mill-direct |
| 150 x 150 | 3.0, 4.0, 5.0, 6.0, 8.0 | 12 m | Mill-direct |
| 160 x 160 | 4.0, 5.0, 6.0, 8.0 | 12 m | Mill-direct |
| 180 x 180 | 4.0, 5.0, 6.0, 8.0, 10.0 | 12 m | Mill-direct |
| 200 x 200 | 4.0, 5.0, 6.0, 8.0, 10.0, 12.0 | 12 m | Mill-direct |
Standards and Grade Equivalence
| Standard | Grade | Yield (MPa) | Tensile (MPa) | Elongation |
|---|---|---|---|---|
| GB/T 6728 | Q195 | 195 | 315-430 | 33 % |
| GB/T 6728 | Q235 | 235 | 370-500 | 26 % |
| GB/T 6728 | Q345 | 345 | 470-630 | 21 % |
| ASTM A500 | Grade B | 290 | 400 | 23 % |
| ASTM A500 | Grade C | 320 | 430 | 21 % |
| EN 10219-1 | S235JRH | 235 | 360-510 | 26 % |
| EN 10219-1 | S275JRH | 275 | 410-560 | 23 % |
| EN 10219-1 | S355JRH | 355 | 470-630 | 22 % |
| JIS G3466 | STKR400 | 245 | 400 | 23 % |
| JIS G3466 | STKR490 | 325 | 490 | 23 % |
Galvanizing Routes Compared
Pre-galvanized (coil-fed)
The flat coil is galvanized at the mill before tube forming. The seam is welded after zinc coating and the weld zone is normally repaired with zinc-rich paint, or the tube is re-galvanized in a finishing bath. Pre-galvanized tube has a uniform exterior finish, lighter zinc coating, and is the cost-effective choice for interior or light-exterior use. Common coating weights: Z60, Z120, Z180, Z275.
Hot-dip galvanized (post-weld)
The welded tube is dipped into molten zinc after forming. The entire surface — inside and outside — receives a uniform zinc layer, with thicker coats typical. Hot-dip galvanized tube is the correct choice for outdoor structural service, marine atmospheres, and buried applications. Common coating weights: Z275 to Z600.
For comparison, EN 10346 and ASTM A653 cover the galvanized coil that feeds the pre-galvanized line, while ISO 1461 and ASTM A123 cover the hot-dip galvanized tube treatment.
Quality Assurance
Every shipment ships with a mill test certificate (EN 10204 3.1 as standard; 3.2 with independent witness available), based on the heat number traceable to the steel coil and tube bundle. Each bundle carries a label listing heat number, size, wall, length, bundle weight, and piece count.
- Chemistry: C, Mn, Si, P, S verified against the grade window (lactam / OES).
- Tensile: yield, ultimate, elongation per ASTM A370 / ISO 6892-1, on a sample per heat.
- Coating mass: gravimetric verification of zinc per ASTM A90 / ISO 1460 on a sample per bundle.
- Dimensional: side, wall, length, straightness, twist on every bundle.
- Visual: surface, spangle, repair spots, seam visibility.
- Weld integrity: 100 % eddy-current testing on the weld seam; flatten test on a sample per heat.
Applications and Engineering Notes
Solar mounting structures: Square tube 50 x 50 x 2.5 mm in Q235 with Z275 hot-dip is the standard ground-mount ramming post for utility-scale solar. Hot-dip beats pre-galvanized in service life when the soil is damp or the climate is humid.
Fence frames: 40 x 40 x 2.0 mm or 60 x 60 x 2.5 mm pre-galvanized with Z120 coating is the cost-effective residential and commercial fence frame. Light coating is fine for inland exposure; bump to Z180 for coastal customers.
Furniture and retail fixtures: 25 x 25 x 1.2 mm or 30 x 30 x 1.5 mm pre-galvanized with minimized spangle and anti-fingerprint topcoat delivers the smooth finish retail-furniture customers want, with the corrosion resistance the warehouse-to-store chain requires.
Architectural balustrades: 50 x 50 x 2.0 mm or 60 x 60 x 2.5 mm in Z275 with skin-passed minimized spangle is a clean architectural surface that can be left natural or powder-coated in the field.
Greenhouse frames: 20 x 20 x 1.2 mm through 50 x 50 x 2.0 mm pre-galvanized with Z180 coating handles the humid greenhouse environment for 8-12 years before re-galvanizing is considered.
Ordering Information
When requesting a quote, please specify:
- Side dimension (A x A) and wall thickness (T).
- Length in meters (6 m standard, others by request).
- Steel grade (Q195 / Q235 / Q345 / S235JRH / A500 Gr.B / etc.).
- Galvanizing route: pre-galvanized or hot-dip.
- Zinc coating class: Z120, Z180, Z275, or other.
- Surface finish: spangled, minimized spangle, or zero spangle (skin-passed).
- Surface treatment: chromate passivation, RoHS-compliant (Cr-free) passivation, oiled, none.
- Mill test certificate level: 3.1 or 3.2.
- Packaging and marking: bundle size, sling requirements, container vs. break-bulk.
- Quantity in metric tons or pieces.
- Destination port and Incoterm.
Packaging and Shipment
- Container: 20-ft container accommodates roughly 22-26 metric tons of bundle-loaded 6 m / 12 m tube. 40-ft HC holds roughly 25-28 metric tons.
- Break-bulk: bundles strapped with steel banding and corner protection, container-bedding plywood base, plastic sleeve, six-sided wrap on heavy export orders.
- Lead time: ex-stock sizes ship 10-15 working days after order confirmation. Mill-direct sizes ship 25-35 working days after order confirmation.
- Documents: commercial invoice, packing list, MTC, country of origin, B/L, insurance, RoHS compliance statement (when applicable), and any FTA certificate you need.
Frequently Asked Questions
Can I get tube with both pre-galvanized exterior and hot-dip galvanized interior?
Yes. Standard pre-galvanized tube has a thin zinc layer on the outside only, with the inside weld-zone bare or repaired-painted. If you need a thicker interior zinc layer for humid-service applications, we run hot-dip post-weld.
Is the tube weld as strong as the base steel?
For non-structural applications, the weld is at least equal to the base metal strength. For structural applications under EN 10219 S235JRH or S275JRH, the weld is tested as part of the heat qualification; full-section tensile results meet the grade window.
Can I powder-coat over the galvanized surface?
Yes. Use a zinc-compatible primer (zinc-rich epoxy) before the powder coat, and powder coat within 30 days of the galvanized surface being exposed (or after sweep-blast cleaning for older surfaces). We can deliver the tube pre-primed on request.
What is the expected outdoor service life?
Pre-galvanized Z180 in mild rural / urban environments typically achieves 15-25 years before significant white rust; Z275 hot-dip achieves 25-40 years in similar exposure. Coastal and industrial environments shorten the rating; consult us with the project’s atmospheric corrosivity category for an honest estimate.
Do you supply ASTM A500 Grade C?
Yes. We dual-certify Q235/S235JRH with A500 Gr.B as standard. A500 Gr.C maps best to Q345 or S355JRH.
What is the standard color difference between batches?
Pre-galvanized tube can vary in spangle brightness and color tone between coils and between galvanizing baths. For visible architectural work, request “minimized spangle” or “skin-passed zero-spangle” for consistency. Hot-dip is uniformly grey.
Request a Quotation
Send your size list, grade, coating requirement, and the destination port to [email protected]. We return a mill-direct offer with MTC, packaging, and the lead time you can schedule into your project’s procurement plan.
Browse Huaxia-Steel for additional structural sections, hollow sections, and mill-direct galvanized steel products.
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