Description
Direct Mill Supply for Structural SHS — Seamless square steel tubes in Q235B and Q355B rolled from our own billets, shipped with full heat-number traceability and EN/ASTM mill certificates.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Seamless Square Steel Tube |
| Product Type | Seamless Square Steel Tube / Square Hollow Section (SHS) |
| Steel Grade | Q195, Q235, Q345 (Q355B), S235JR, S275JR, S355JR, A500, 20#, S20C, S10C, S15C |
| Standard | GB, ASTM A213, DIN EN 10217-1, ASTM A500, JIS G3466 |
| Section Shape | Square |
| Size Range | 15×15 mm – 500×500 mm (rectangular up to 800×1200 mm) |
| Wall Thickness | 0.5 – 12 mm |
| Length | 5.8 – 12 m (or as required) |
| Technique | Seamless / Hot Rolled |
| Surface Treatment | Black, Bright, Galvanized (40–500 g/m²), Painted |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures, construction frames, machinery, scaffolding, furniture, industrial frameworks |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC & General Contractors | Building frames, warehouse columns, portal steel structures |
| Mechanical Fabricators | Equipment support bases, conveyor frames, machine guards |
| Construction Companies | Scaffolding uprights, temporary works bracing, site access platforms |
| Infrastructure Developers | Bridge handrails, pipe rack supports, industrial platform grating frames |
What Negative Tolerance Really Costs on a Structural Frame Order
A 0.4 mm wall deficit on a Q355B column can void an entire batch at third-party inspection.
Overseas buyers sourcing seamless square steel tubes from overseas fabricators often discover dimensional shortfalls only after the container reaches the destination port. When wall thickness falls below the specified minimum, the structural engineer rejects the batch, the general contractor faces schedule delays, and the procurement team is left negotiating claims across time zones. Material traceability gaps make it worse — if the fabricator sourced steel from a third-party trader, heat numbers on the mill test certificate may not match the physical stamps on the tubes. [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed and seamless hollow sections]
Matching Load-Bearing Requirements for Industrial Steel Structures
Seamless square steel tubes in Q355B and S355JR grades carry higher yield strength than mild steel alternatives, making them suitable for primary load-bearing columns and beam-to-column connections in portal frame buildings. The seamless hot-rolled process produces uniform wall thickness around the entire perimeter — critical when tubes are welded into moment-resisting frames where stress concentrations occur at joints. For EPC firms building warehouses and industrial plants across the Middle East and Southeast Asia, specifying Q355B seamless square steel tubes with ±1% tolerance ensures that shop drawings match as-fabricated dimensions, reducing RFI cycles and on-site rework.
Structural Code Compliance and Surface Protection Selection
Engineering specifications for steel structures typically reference EN 1993 (Eurocode 3) or AISC 360, both of which require verified material properties and documented production controls. For projects shipping to the EU, CE marking under EN 10210 or EN 10219 is mandatory for structural hollow sections — customs authorities may hold shipments lacking proper certification. Surface treatment selection depends on the service environment: hot-dip galvanized coatings (40–500 g/m²) protect against atmospheric corrosion in coastal industrial zones, while black or painted finishes suit indoor machinery frames where appearance matters less than cost. [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 1090]
Steel Grade Equivalence and Seamless Manufacturing Principles
The Q-series (Q235B, Q355B) follows the Chinese GB standard system, where the number indicates minimum yield strength in MPa. The S-series (S235JR, S275JR, S355JR) follows the European EN system with similar yield strength designations but different impact testing requirements — the “JR” suffix denotes 27J Charpy impact energy at room temperature. ASTM A500 Grades B and C serve the North American market with comparable strength tiers. Seamless hot-rolled tubes are produced by piercing a solid billet and elongating it over a mandrel, resulting in no longitudinal weld seam — this eliminates the weld-line weakness present in ERW tubes and provides consistent mechanical properties in all directions, which matters when tubes are bent, punched, or welded from multiple angles on a fabrication floor. Wall thickness from 0.5 mm to 12 mm covers everything from light furniture frames to heavy industrial columns, and the ±1% tolerance ensures that theoretical weight calculations match actual delivered weight within acceptable commercial limits.
The Hidden Cost of Unverified Material Sources
Purchasing seamless square steel tubes from a trader who sources from multiple mills creates a documentation chain with gaps. When the destination country requires EN 10204 3.2 certificates — meaning a third-party inspector must witness the mechanical testing — a mixed-heat batch cannot pass. The result is either costly re-inspection at the port or outright rejection. Negative tolerance abuse compounds the problem: a tube stamped Q355B with actual wall thickness 0.4 mm below nominal may look identical on the outside but carries significantly less load capacity, creating a structural safety risk that only surfaces during engineering audit or, worse, under service load. [NEED_CITE: material traceability and heat number requirements under EN 10204]
Why Procurement Teams Choose Our Mill-Direct Supply
We operate our own steel production facility with three rolling lines and over 2,800 specifications of raw material inventory, meaning every seamless square steel tube we ship starts as a billet we selected and controlled. Our fabrication division handles downstream processing — CNC cutting, drilling, welding per approved WPS, shot blasting, and painting — so project teams receive fabricated components with a single quality system and one point of accountability. We maintain certified welding procedures (AWS and EN qualified welders), complete quality documentation packages including weld maps and dimensional inspection reports, and track record delivering to EU, Middle East, Southeast Asian, and African project sites. Third-party inspection through SGS, BV, or TÜV is arranged at our facility before shipment, not after the goods arrive. Custom sizes outside standard ranges are produced to engineering drawings with full shop drawing review and material optimization support.
Documentation & Compliance
- Mill test certificate documenting Q235B and Q355B chemical composition and mechanical properties per GB/T 700 and GB/T 1591, with heat number traceability
- CE certificate confirming compliance with EN 10210 and EN 10219 for structural hollow sections shipped to EU member states
- ISO 9001 quality management system certificate covering the full production process from billet reheating to final dimensional inspection
- SGS or BV third-party inspection report verifying wall thickness, outer dimensions, and surface coating weight against purchase specifications
- Material traceability report linking each tube bundle to its original heat number, billet cast, and rolling schedule
- Export customs documents including packing list, bill of lading, and certificate of origin formatted for destination-country clearance
Packaging, Loading & Delivery
- Q355B seamless square steel tubes bundled with galvanized steel strips at intervals matched to the 5.8–12 m length range, preventing bundle shift during ocean transit
- Galvanized tubes (40–500 g/m² coating) packed with edge protectors and waterproof interleave to preserve zinc layer integrity during humid coastal transport
- Container loading plans optimized for 15×15 mm to 500×500 mm size ranges, nesting smaller sections inside larger ones to maximize payload per 20ft or 40ft container
- Custom cut-to-length service available for 12 m tubes, with plain ends deburred and marked with heat number, steel grade, and size at each piece
- Shipment terms available as FOB, CIF, or DDP to project sites across the Middle East, Southeast Asia, Africa, and South America
Starting Your Procurement Process
Share your project drawings (PDF or DWG), required steel grades, quantities, and destination port — our engineering team responds within one day with a preliminary assessment covering material availability, fabrication feasibility, and certification requirements. For non-standard sizes or custom wall thickness outside the 0.5–12 mm range, we provide shop drawing review and production scheduling before contract signing.
Request a Quote with Mill Test Certificates
Send your specifications and required standards to receive pricing, production lead time, and complete documentation packages.
Mobile/WhatsApp/WeChat: +86 188 5315 7756 | Email: admin@xjystructure.com
Frequently Asked Questions
Q: How do Q235B and Q355B compare to S235JR and S355JR for EU projects?
A: Q235B and S235JR share similar yield strength levels, as do Q355B and S355JR. The key difference lies in impact testing requirements — S-series grades under EN standards specify Charpy impact energy at defined temperatures, while Q-series under GB standards follow different testing protocols. For EU projects requiring CE marking, we supply tubes meeting EN 10210 or EN 10219 with full EN 10204 3.1 or 3.2 certificates.
Q: Can you arrange third-party inspection before shipment?
A: Yes. SGS, BV, and TÜV inspections are conducted at our facility during production or before loading. The inspection covers dimensional verification, wall thickness measurement, surface coating weight (for galvanized tubes), and witness testing for mechanical properties. Reports are issued with heat number traceability.
Q: What is the minimum order quantity for custom sizes?
A: The standard MOQ is 1 Ton. For non-standard outer dimensions or wall thickness outside the 15×15 mm to 500×500 mm and 0.5–12 mm ranges, we review engineering drawings and confirm production feasibility before quoting.
Q: How is invoicing calculated — theoretical weight or actual weight?
A: Invoicing follows the purchase agreement. Standard commercial practice for seamless square steel tubes uses theoretical weight based on nominal dimensions and standard density, with the ±1% tolerance ensuring minimal deviation. If actual weight invoicing is required, we provide weighbridge certificates at loading.
Q: What surface treatment options are available for corrosive environments?
A: We offer hot-rolled black finish, bright finish, hot-dip galvanized coating (40–500 g/m²), and painted finishes. For coastal or industrial atmospheres, galvanized coating provides long-term corrosion protection. For indoor structural frames or machinery, black or painted finishes offer cost efficiency.
