Description
Direct Mill Supply — Vertically integrated from raw steel to finished Q235B Q355 square rectangular steel tube
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355 Square and Rectangular Carbon Steel Tube |
| Product Type | Square / Rectangular Steel Tube (Hollow Section) |
| Steel Grade | Q195, Q215, Q235, Q235B, Q345, Q355, Q355B, S235JR, S355JR, S355J2H, S355J0H, ASTM A53 Grade A, ASTM A53 Grade B, ASTM A500 Grade A, ASTM A500 Grade B, ASTM A500 Grade C, ASTM A36, STK400, SS400, ST42.2, S195 |
| Standard | EN 10219, EN 10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A53, ASTM A36 |
| Section Shape | Square / Rectangular |
| Size Range | Square: 20×20 mm – 500×500 mm; Rectangular: 20×40 mm – 300×500 mm |
| Wall Thickness | 0.5 – 30 mm |
| Length | 3 – 12 m (random or cut-to-length) |
| Technique | Hot Rolled / Welded (ERW) |
| Surface Treatment | Pre-galvanized (Zn 40–80 g/m²), Hot-dip galvanized (Zn 200–600 g/m²), Hot Rolled, or as per customer requirement |
| Tolerance | ±1% |
| Ends | Plain / Customized |
| Application | Steel structure engineering, construction frames, solar support structures, machinery manufacturing, greenhouse frames, fence posts, bridges, lifting machinery |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Building | Steel frame structures, columns, beams, trusses, platforms, stairways, glass curtain wall supports |
| Industrial & EPC Projects | Factory warehouses, power plant support frames, pressure vessel components, oil storage tank structures |
| Infrastructure & Renewable Energy | Solar panel support structures, bridge railings, airport construction frameworks |
| Agricultural & Light Structures | Greenhouse frames, fence posts, agricultural machinery frames |
| Heavy Machinery & Transport | Automobile chassis, lifting and transportation machinery, conveyor structures |
Where Steel Grade Equivalence Between EN and ASTM Standards Decides Customs Clearance
Mismatched grade documentation is the single most common reason for customs delays on structural hollow sections.
When procurement teams specify Q235B or Q355B on purchase orders but the project engineer’s drawings call for S235JR or S355JR per EN 10219, or ASTM A500 Grade B per American standards, the gap between what was ordered and what the mill test certificate shows can halt an entire shipment at the port. [NEED_CITE: steel grade equivalence between EN 10219 and ASTM A500 standards] Overseas buyers frequently discover this mismatch only after the container arrives, triggering re-inspection demands, rejected material, or costly resubmission of compliance paperwork. The problem deepens when fabricators source raw material from third-party mills without maintaining heat-level traceability — the certification chain breaks, and no amount of re-testing can reconstruct it.
How Wall-Thickness Tolerance Directly Affects Structural Frame Load Calculations
A ±1% tolerance on wall thickness sounds tight on paper, but on a 500×500 mm square tube with 20 mm wall, even a slight negative drift across a batch can shift the actual weight and load-bearing capacity enough to fail third-party inspection at the project site. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements] Engineers designing to EN 1993 or AISC specifications calculate member capacity based on nominal dimensions — when the delivered product falls below the minimum specified thickness, the structural node fails verification regardless of whether the steel grade itself is correct. This is why Q235B Q355 square rectangular steel tube suppliers who control both rolling and finishing under one roof can guarantee tolerance consistency across the full order, rather than blending stock from multiple sources with different mill practices.
Compliance Requirements Across Engineering Standards and Corrosive Environments
Structural hollow sections used in load-bearing frames must comply with the execution class requirements of EN 1090 for EU-bound projects, or meet AISC certification standards for North American destinations. [NEED_CITE: EN 1090 execution class compliance for structural steel fabrication] For projects in coastal or industrial corrosive environments, the choice between pre-galvanized coating at 40–80 g/m² and hot-dip galvanizing at 200–600 g/m² directly determines service life before first maintenance. Q355B and S355JR grades offer higher yield strength for heavy-load columns and long-span trusses, while Q235B and S235JR remain the default for secondary structures and bracing where weight optimization is less critical. Cut-to-length delivery up to 12 m eliminates on-site splicing for standard floor heights, and plain ends can be prepared for welding, bolting, or mechanical connection per project specifications.
Understanding the Q-Series, S-Series, and ASTM Grade Systems for Hollow Sections
The Q-series (Q195, Q235B, Q355B) follows the Chinese GB/T standard system where the number after “Q” indicates the minimum yield strength in MPa. The S-series (S235JR, S355JR, S355J2H) follows the European EN system, with the suffix indicating impact test temperature and energy requirements — JR for room temperature, J0 for 0°C, J2 for −20°C. ASTM A500 grades (A, B, C) follow the American system with progressively higher yield and tensile strength requirements. These systems are not interchangeable by name, but they are equivalent by mechanical performance: Q235B maps closely to S235JR and ASTM A53 Grade A; Q355B maps to S355JR and ASTM A500 Grade B. [NEED_CITE: steel grade equivalence mapping between GB/T, EN, and ASTM structural steel standards] ERW welding produces a longitudinal seam suitable for most structural applications, while hot-rolled hollow sections offer superior corner mechanical properties for heavy-load or seismic-zone projects. Pre-galvanized tubes provide economical corrosion protection for indoor or mild environments, while hot-dip galvanizing is specified for outdoor exposure, coastal installations, or agricultural structures where moisture and chemical agents accelerate corrosion.
The Hidden Cost of Ordering Without Verified Grade Documentation
Purchasing Q235B Q355 square rectangular steel tube without confirmed mill test certificates tied to specific heat numbers creates a chain of risk: the material may pass visual inspection at the port, but fail chemical composition verification during third-party testing at the project site. [NEED_CITE: structural steel material traceability requirements for international projects] Customs authorities in the EU, Middle East, and Africa increasingly require EN 10204 3.1 or 3.2 certificates with traceable heat numbers — shipments without proper documentation face rejection, bonded warehouse fees, or forced re-export. Beyond customs, unverified material creates structural liability: if a welded connection fails during service and the steel grade cannot be confirmed against the design specification, the entire project faces legal and safety exposure that far exceeds the original material cost saving.
Why Procurement Teams Choose Vertically Integrated Mill-to-Fabrication Supply
XJY Structure operates its own steel mill with three production lines and maintains over 2,800 raw material specifications in stock, meaning every Q235B Q355 square rectangular steel tube order begins with material we produce and control — not material sourced from third-party traders with unknown mill origins. Our fabrication workshop performs CNC cutting, drilling, bending, and welding (MIG/MAG/SAW) on the same site, so shop drawings are executed against the actual material batch rather than generic catalog specifications. Welding procedures are certified per AWS and EN standards, with qualified welders and complete documentation including WPS, PQR, weld maps, and dimensional inspection reports. For EU projects, we supply EN 1090 execution class compliance; for international projects requiring third-party verification, SGS and BV inspections are arranged before shipment. Professional loading plans for oversized and heavy fabricated components are developed in-house, drawing on years of experience shipping to West Africa, the Middle East, and Southeast Asia.
Documentation & Compliance
- Mill Test Certificate documenting Q235B / Q355B chemical composition and mechanical properties per GB/T 6728, with EN 10204 3.1 format for international projects
- CE Certificate confirming compliance with EN 10219 and EN 10210 for cold-formed and hot-formed structural hollow sections destined for EU markets
- ISO 9001 Quality Management System certificate covering the full production chain from steelmaking through fabrication and surface treatment
- SGS or BV third-party inspection report verifying dimensional accuracy, coating thickness, and weld quality before container sealing
- Full material traceability by heat number linking each Q235B Q355 square rectangular steel tube bundle to its original melt chemistry and rolling record
- Export documentation package including packing list, bill of lading, and certificate of origin formatted for destination-country customs requirements
Packaging, Loading & Delivery
- Q235B and Q355 square rectangular steel tubes bundled with high-tensile steel strips and edge protectors to prevent surface damage and preserve galvanized coating during ocean transit
- Pre-galvanized and hot-dip galvanized tubes wrapped with waterproof paper and plastic sleeves to block moisture contact during container shipping to tropical and coastal destinations
- Container loading plans optimized for 5.8 m and 11.8 m internal lengths, maximizing payload for 20ft and 40ft shipments while maintaining weight distribution for crane handling at site
- Cut-to-length service available across the full 3–12 m range, with bundles tagged by length, steel grade, and heat number for rapid site identification and inventory control
- Each bundle marked with heat number, steel grade (Q235B / Q355B), section dimensions, wall thickness, and production date for full traceability from mill to installation
- Delivery terms available as FOB, CFR, CIF, or DDP, with door-to-door logistics coordination for project sites across West Africa, the Middle East, Southeast Asia, and South America
How to Request a Complete Quotation with Mill Test Documentation
Submit your project drawings (PDF or DWG), required steel grades, section dimensions, wall thickness, surface treatment preference, and destination port — we return a detailed quotation within 24 hours including material cost, fabrication charges, coating, packing, and shipping, along with the shop drawing timeline and production schedule. For non-standard dimensions or custom lengths outside the 20×20 to 500×500 mm range, our engineering team reviews feasibility and provides a fabrication proposal before contract signing.
Start Your Q235B Q355 Square Rectangular Steel Tube Inquiry
Send your specifications and required standards to receive a detailed quotation with mill test certificate preview and production timeline.
Mobile/WhatsApp/WeChat: +86 188 5315 7756 | Email: admin@xjystructure.com
Frequently Asked Questions
Q: How do Q235B and Q355B correspond to European EN and American ASTM standards?
A: Q235B is mechanically equivalent to S235JR per EN 10219 and ASTM A53 Grade A. Q355B corresponds to S355JR per EN 10219 and ASTM A500 Grade B. We supply full grade equivalence documentation with every shipment so that the mill test certificate matches the standard specified on your project drawings.
Q: What quality documentation is supplied with each order of Q235B Q355 square rectangular steel tube?
A: Every order is accompanied by a Mill Test Certificate (EN 10204 3.1 format) documenting chemical composition and mechanical properties by heat number. For EU projects, we provide CE certification per EN 10219/EN 10210. Third-party inspection reports from SGS or BV are available upon request before shipment.
Q: Can you produce non-standard sizes or custom lengths outside the listed range?
A: Yes. Our own steel mill and fabrication workshop allow us to produce custom section dimensions, wall thicknesses, and cut-to-length sizes beyond the standard 20×20 to 500×500 mm range. Share your drawing or specification, and our engineering team confirms feasibility and lead time before contract.
Q: What surface treatment options are available and how do I choose?
A: We offer pre-galvanized (Zn 40–80 g/m²) for indoor or mild environments, hot-dip galvanized (Zn 200–600 g/m²) for outdoor, coastal, or agricultural exposure, and hot-rolled or painted finishes for industrial or project-specific requirements. The choice depends on the corrosion environment and design service life specified by your engineer.
Q: How do you handle loading and shipping for oversized or heavy structural tubes?
A: Our logistics team develops professional loading and lashing plans for each shipment, accounting for section size, wall thickness, and container dimensions. We have direct experience shipping structural steel to West Africa, the Middle East, and Southeast Asia, and coordinate full export documentation and tracking through to site delivery.
