Description
Factory-direct Q235B Q345B hot rolled carbon steel square rectangular tube manufacturer — 2,800+ specifications produced on 3 dedicated lines with in-house lab testing before every shipment.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q345B Hot Rolled Carbon Steel Square & Rectangular Tube |
| Product Type | Square and Rectangular Steel Tube (Welded / Seamless) |
| Steel Grade | Q195, Q215, Q235B, Q345B (Q355), S235JR, S355JR, S355J0H, S355J2H, ASTM A500, ASTM A53, ASTM A106, A36, STK400, SS400, ST42.2, #20, #45 |
| Standard | EN 10219, EN 10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A53, ASTM A106, ASTM A36 |
| Section Shape | Square / Rectangular / Round |
| Size Range | Square 20×20 mm – 500×500 mm; Rectangular 20×40 mm – 300×500 mm |
| Wall Thickness | 0.5 mm – 30 mm |
| Length | 3 m – 12 m (random / fixed) |
| Technique | Hot Rolled / ERW Welded / Seamless |
| Surface Treatment | Hot Rolled, Pre-galvanized (Zn 40–80 g/m²), Hot Dipped Galvanized (Zn 200–600 g/m²), Oiled, Black, Custom |
| Tolerance | ±1% |
| Ends | Plain / Beveled / Threaded |
| Application | Steel structures, construction frames, solar structures, greenhouse frames, fence posts, machinery, shipbuilding, power engineering, pressure vessels, oil storage tanks, bridges, highway railings, fluid transportation, boiler construction |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors & Construction | Steel structure frames, solar mounting systems, high-rise building columns, bridge support members |
| Machinery Manufacturers | Conveyor system frames, industrial platform supports, equipment base structures |
| Infrastructure & Energy | Power station structural frames, pressure vessel shells, oil storage tank rings, highway guardrail posts |
| Agricultural & Commercial | Greenhouse skeleton tubes, warehouse racking uprights, fence post systems |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A ±1% tolerance on a 30 mm wall Q345B tube is the difference between passing third-party inspection and watching an entire container get rejected at the destination port.
I once loaded a batch of square tubes for a Saudi EPC project. The mill cert looked clean, but when the client’s third-party inspector pulled random pieces at Jeddah, the wall thickness on several tubes fell below the negative tolerance limit allowed by EN 10219. The whole shipment was held. Re-sorting, re-testing, and reshipping cost more than the original margin. [NEED_CITE: EN 10219 cold-formed structural hollow section tolerance requirements] Since then, every Q235B Q345B hot rolled carbon steel square rectangular tube manufacturer order leaving our facility goes through our own physical and chemical lab first — actual measured data, not theoretical weight calculations, determines whether the batch ships.
Matching Load-Bearing Demands Across Structural Applications
Q235B Q345B hot rolled carbon steel square rectangular tube profiles in 500×500 mm with 30 mm walls carry primary frame loads in high-rise steel structures and long-span bridge components, while lighter sections like 20×20 mm at 1.5 mm wall serve greenhouse and fence applications where dead load is minimal. Our hot rolled and ERW welded lines cover both ends of this spectrum from a single procurement source, so EPC contractors do not need to split orders across specialty mills and general traders. The proprietary sharp-corner rectangular tube technology — one of 41 patents — delivers tight corner radii that sit flush against gusset plates and connection brackets, reducing welding gaps and improving load transfer in moment frames.
Engineering Code Compliance and Surface Protection Selection
Structural frames designed to EN 1993 require hollow sections conforming to EN 10219 or EN 10210, with CE marking mandatory for EU market entry; North American projects typically specify ASTM A500 Grade B or C. [NEED_CITE: steel grade equivalence between EN 10219 and ASTM A500 standards] Corrosion environment dictates surface treatment: pre-galvanized at 40–80 g/m² suits indoor machinery frames, while hot dipped galvanized at 200–600 g/m² is specified for outdoor solar mounting structures and bridge railings exposed to moisture. Fixed-length cutting to site-specific dimensions reduces on-site waste and welding joints, particularly on 12 m standard lengths used for column-to-column runs.
Steel Grade Systems and Hot Rolling Process Fundamentals
Q235B and Q345B belong to the Chinese GB/T 1597 carbon and low-alloy structural steel system, where the number after “Q” indicates minimum yield strength in MPa. Q235B maps closely to S235JR under EN 10025 and ASTM A36 under the US system, while Q345B (now designated Q355 under GB/T 1597-2018) aligns with S355JR and ASTM A572 Grade 50 in general structural use. [NEED_CITE: steel grade equivalence between Q235B S235JR and ASTM A36] Hot rolling produces the square and rectangular profiles at temperatures above recrystallization point, yielding uniform grain structure and tighter dimensional consistency across the 0.5–30 mm wall range compared to cold-formed alternatives. For pressure-containing applications like boiler tubes and oil storage tank nozzles, seamless processing per ASTM A106 eliminates the weld seam entirely.
Hidden Costs of Unverified Material Procurement
Ordering Q345B tubes based on price alone, without mill test certificates traceable to heat numbers, risks receiving off-grade material that fails mechanical testing at destination — leading to customs holds, project re-inspection fees, and structural safety concerns if substandard tubes are already welded into frames. Missing CE documentation under EN 10210 or EN 10219 triggers EU customs rejection regardless of physical quality. [NEED_CITE: EU construction products regulation CE marking requirements for structural steel] Negative tolerance abuse — where actual wall thickness consistently falls at the lower boundary — reduces load-bearing capacity below design calculations, creating liability exposure for EPC contractors signing off on structural integrity.
Procurement Confidence from Mill to Job Site
As a Q235B Q345B hot rolled carbon steel square rectangular tube manufacturer operating our own 3 production lines, we eliminate trader markups and provide direct mill test certificates from our in-house physical and chemical laboratory. The 2,800+ specification range covers square, rectangular, and round sections across all listed steel grades, so a single purchase order handles structural columns, purlins, and bracing tubes without splitting suppliers. Every shipment carries CE certification under EN 10210 and EN 10219 for EU compliance, ISO 9001:2015 quality system documentation, and optional SGS or BV third-party inspection reports. Custom non-standard dimensions and fixed-length cutting are produced to order, and our logistics team prepares container loading plans optimized for 20ft and 40ft units with FOB, CIF, or DDP terms to 50+ countries.
Documentation & Compliance
- Mill Test Certificate documenting Q235B or Q345B chemical composition and mechanical properties per GB/T 1597, with heat number traceability
- CE certificate confirming compliance with EN 10210 for seamless hollow sections or EN 10219 for welded hollow sections, required for EU customs clearance
- ISO 9001:2015 quality management system certificate covering production and inspection processes
- SGS or BV third-party inspection report available upon request, verifying wall thickness, dimensions, and surface quality before loading
- Material traceability report linking each bundle to heat number, chemical analysis, and tensile test results
- Customs document package including packing list, bill of lading, and certificate of origin for destination-country clearance
Packaging, Loading & Delivery
- Hot rolled Q235B and Q345B tubes bundled with steel strips and edge protectors, preventing surface scratches and corner damage during ocean transit
- Pre-galvanized and hot dipped galvanized square rectangular tubes wrapped with waterproof paper and plastic sleeves to preserve zinc coating integrity
- Container loading plans optimized by our logistics team for 3 m–12 m fixed lengths, maximizing weight utilization in 20ft and 40ft units
- Fixed-length cutting service available to project-specified dimensions, reducing on-site waste and welding joints for structural frame assembly
- Heat number and steel grade stenciled on each tube end for site identification and inspection traceability
- FOB, CIF, and DDP shipping terms available with real-time tracking to ports across EU, North America, Southeast Asia, Middle East, and 50+ countries
Requesting a Project-Specific Quotation
Submit your specification sheet — including section dimensions, wall thickness, steel grade, total tonnage, and destination port — to receive a detailed quotation with unit pricing, production lead time, and applicable certification documentation. Non-standard dimensions and custom surface treatment requirements are reviewed by our engineering team for feasibility and pricing. Mill test certificates and third-party inspection arrangements are confirmed at the contract stage before production begins.
Frequently Asked Questions
Q: How do Q235B and Q345B compare to S235JR and S355JR in international projects?
A: Q235B provides equivalent yield strength and chemical composition to S235JR under EN 10025 and ASTM A36 under US standards, making it suitable for general structural frames. Q345B (Q355) offers higher yield strength matching S355JR and ASTM A572 Grade 50, used in heavy-load bearing structures. We supply mill test certificates showing actual test values so your engineer can verify equivalence for your specific design code.
Q: Can you produce non-standard dimensions below the 1 Ton MOQ?
A: Yes. While standard catalog sizes carry a 1 Ton MOQ, our 3 dedicated production lines handle custom non-standard dimensions and small-batch orders for project-specific requirements. Contact us with your drawing or specification for feasibility review and pricing.
Q: What is the difference between pre-galvanized and hot dipped galvanized surface treatment?
A: Pre-galvanized tubes carry a zinc coating of 40–80 g/m² applied before forming, suitable for indoor or mild corrosion environments like machinery frames and indoor racking. Hot dipped galvanized tubes receive 200–600 g/m² zinc coating after forming, providing superior corrosion resistance for outdoor applications such as solar mounting structures, bridge components, and coastal installations.
Q: How do you verify wall thickness tolerance before shipment?
A: Every production batch undergoes dimensional inspection in our in-house physical laboratory using calibrated ultrasonic thickness gauges. Actual measured data is recorded on the mill test certificate. Third-party inspection by SGS or BV can be arranged before loading to independently verify wall thickness, dimensions, and surface quality against EN 10219 or ASTM A500 tolerance requirements.
Q: What certifications do you provide for EU and North American projects?
A: EU projects receive CE certification under EN 10210 for seamless sections or EN 10219 for welded sections, along with ISO 9001:2015 documentation. North American projects are supplied with mill test certificates conforming to ASTM A500, A53, or A106 as specified. SGS or BV third-party inspection reports are available for both markets.
Get Your Q235B Q345B Structural Tube Quotation Today
Send your specifications, steel grade, and destination port to receive pricing, mill test certificate samples, and production scheduling within 12 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjysteel.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjysteel.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
