Description
Factory-Direct Sharp-Corner Tubes — Every Q235B and Q345B batch rolls through our own ERW lines with original mill test certificates before container sealing.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q345B Sharp Corner Square and Rectangular Steel Tube |
| Product Type | Sharp Corner Square and Rectangular Steel Tube (SHS / RHS) |
| Steel Grade | Q235B, Q345B |
| Standard | GB/T 6728; other international standards available upon request |
| Section Shape | Square / Rectangular (Sharp Corner / Right-Angle) |
| Size Range (Width) | 150–625 mm |
| Length | 5–15 m (standard 5.8 m / 6 m / 12 m available) |
| Technique | ERW (Electric Resistance Welded) |
| Surface Treatment | Hot Rolled / Hot-Dip Galvanized (HDG) |
| Tolerance | ±1% |
| Ends | Plain ends; cutting, bending, punching, welding available |
| Application | Construction building, steel structures, machinery frames, scaffolding, architectural fabrication |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Building | Steel column frames, beam-to-column connections, architectural sharp-corner curtain wall supports |
| Machinery Manufacturing | Equipment base frames, conveyor structures, robotic arm housings requiring tight right-angle tolerance |
| Infrastructure & Scaffolding | Heavy-duty scaffolding uprights, industrial platform supports, bridge formwork systems |
What ±1% Tolerance Actually Means When Your Steel Frame Has 200 Connections
A millimeter of deviation at one corner compounds across a full structural grid.
On a machinery frame with dozens of bolted joints, a sharp-corner square tube that is even slightly out of square forces fitters to ream holes or shim plates on-site. I have seen entire scaffold batches rejected at port because the right angles measured 91 degrees instead of 90 — the rework cost more than the steel. When you source a Q235B Q345B sharp corner square rectangular steel tube supplier, the tolerance claim on the datasheet only matters if the factory measures every bundle before loading. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements]
How Sharp-Corner Profiles Match Structural Frame Assembly
Right-angle SHS and RHS sections sit flush against gusset plates and mating members without the gap that round tubes or radiused corners leave. On a Q235B Q345B sharp corner square rectangular steel tube supplier order for building frames, the ±1% tolerance ensures that pre-drilled connection plates align without field modification. Our ERW lines hold the corner geometry consistently across the 150–625 mm width range, so a 300 × 300 mm column meets the same squareness as a 600 × 200 mm beam — critical when a single project mixes both profiles.
Engineering Compliance and Surface Selection for Project Environments
Structural designers specifying Q235B or Q345B grade tubes need documentation that matches the governing code — GB/T 6728 for domestic projects, or equivalent EN 10210 / EN 10219 certification when the structure ships to Europe. Hot-dip galvanized finish is the default for outdoor scaffolding and coastal infrastructure where corrosion protection extends service life without painting. Hot-rolled black finish suits indoor machinery frames where welding and secondary coating follow fabrication. For EU-bound shipments, Lloyd’s CE certification under EN 10210/10219 clears customs without additional testing at destination. [NEED_CITE: steel grade equivalence mapping between GB Q-series and EN S-series standards]
Steel Grade, Welding Method, and Corner Geometry Explained
Q235B and Q345B belong to the Chinese GB standard system — Q235B offers general structural strength, while Q345B provides higher yield capacity for load-bearing columns and long-span beams. Both grades weld cleanly under ERW (Electric Resistance Welded) process, which forms the longitudinal seam without filler metal, keeping cost lower than seamless while maintaining consistent wall thickness around the sharp corner. The sharp-corner forming process itself is what separates these tubes from standard radiused RHS: dedicated roll passes bend the strip at near-90-degree angles, producing a tight internal radius that maximizes section modulus and allows flush mechanical connections. Hot-dip galvanizing after forming coats all four corners and the weld seam uniformly, whereas hot-rolled finish preserves the mill scale for buyers who will paint or powder-coat after fabrication. Wall thickness tolerance of ±1% means the theoretical weight used for invoicing stays close to actual delivered weight — a point that matters on bulk orders where a few percent of excess thickness adds up to tons of unbudgeted cost.
Hidden Costs When Corner Tolerance and Certification Fall Short
A container of sharp-corner tubes that arrives with corner angles deviating beyond ±1% forces the contractor to either accept structural misalignment or cut and re-weld connections — both options erase the price advantage of buying direct. Missing or incomplete mill test certificates trigger customs holds at destination ports, especially in markets that enforce CE marking for structural steel. [NEED_CITE: customs documentation requirements for structural steel imports under CE marking regulations] Material traceability gaps — no heat number linking the tube back to the original coil — can void engineering liability coverage on certified projects. The real cost is never the per-ton price difference; it is the crane idle time, the re-inspection fees, and the delayed handover penalty.
Why Bulk Buyers Return for Repeat Orders
Every Q235B and Q345B sharp-corner tube we ship carries an original mill test certificate documenting chemical composition and mechanical properties — not a generic template. Our factory runs three ERW lines simultaneously, holding 2,800+ specifications in ready stock so that standard sizes ship within days while custom non-standard widths or lengths roll within typical production lead times. Each batch is available for SGS or BV third-party inspection before container sealing. We handle export documentation, container loading optimization, and customs paperwork in-house, so a single point of contact manages your order from inquiry to port discharge. Long-term partners receive volume-based pricing reviews every six months.
Documentation & Compliance
- Mill test certificate documenting Q235B or Q345B chemical composition and mechanical properties per GB/T 6728, linked to heat number
- Lloyd’s CE certificate under EN 10210 / EN 10219 for structural hollow sections shipped to European markets
- ISO 9001:2015 quality management certificate covering the full ERW production and inspection process
- SGS or BV third-party inspection report available on request, covering dimensional check, coating thickness, and visual weld quality
- Material traceability report mapping each bundle to its original coil heat number for project audit compliance
- Full customs document package including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Q235B and Q345B sharp-corner tubes bundled with steel strips and edge protectors to prevent corner damage during ocean transit
- Hot-dip galvanized surfaces wrapped with waterproof paper and nylon bands to preserve zinc coating integrity in humid container conditions
- Container loading plans optimized for 5.8 m / 6 m / 12 m standard lengths across 150–625 mm width range to maximize payload per 20GP or 40HQ
- Cutting to exact project lengths available before shipment, reducing on-site waste and handling for construction buyers
- Each bundle marked with heat number, steel grade (Q235B or Q235B), and dimensional specification for site identification
- FOB, CIF, and DDP terms available with professional export team coordinating port clearance and door-to-door logistics
Start Your Bulk Procurement With Verified Documentation
Submit your specification sheet — including width, wall thickness, length, steel grade (Q235B or Q345B), surface finish, and destination port — to receive a factory-direct quotation with volume pricing and delivery schedule. We provide sample sections and original mill test certificates for your quality team to verify before contract signing. Non-standard sharp-corner profiles outside the 150–625 mm range are available for custom order discussion.
Request Factory-Direct Pricing and Mill Test Certificates
Send your specification list via email or WhatsApp to receive a bulk quotation with original mill test certificates within hours.
Email: admin@sdxinjiyuan.com
Mobile / WhatsApp: +86 188 5315 7756
Frequently Asked Questions
Q: Can you supply sharp-corner square and rectangular tubes outside the 150–625 mm standard width range?
A: Yes. Our factory holds 2,800+ specifications in ready stock for standard sizes, and we produce custom non-standard widths and wall thicknesses on dedicated ERW lines. MOQ for custom orders remains flexible, starting from 1 ton.
Q: What is the difference between hot-dip galvanized and hot-rolled finish for Q235B Q345B sharp corner tubes?
A: Hot-dip galvanized (HDG) finish provides a zinc coating for corrosion resistance, suitable for outdoor structures, scaffolding, and coastal environments. Hot-rolled black finish retains the mill scale and is preferred for indoor machinery frames where the buyer will apply painting or powder coating after fabrication.
Q: Do you provide CE certification for shipments to European markets?
A: Yes. Our sharp-corner square and rectangular tubes carry Lloyd’s CE certification under EN 10210 and EN 10219 standards, along with complete export documentation to support customs clearance in EU member states.
Q: How does theoretical weight invoicing work with the ±1% tolerance?
A: Orders are invoiced by theoretical weight calculated from nominal dimensions and standard density. The ±1% tolerance ensures that actual delivered weight stays close to theoretical weight, so bulk buyers are not paying significant excess material cost.
Q: Can I arrange third-party inspection before shipment?
A: Yes. SGS and BV third-party inspection services are available on request. The inspection covers dimensional verification, coating thickness measurement for galvanized tubes, weld quality, and material traceability against the mill test certificate.
