Description
Factory-direct pricing without middlemen — Q235B and Q355B seamless square steel tubes roll from our own hot-rolled lines and ship with full mill documentation, cutting agent markups from your structural budget.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Carbon Steel Seamless Square Tube |
| Product Type | Seamless Square Steel Tube / Seamless Square Hollow Section (SHS) |
| Steel Grade | Q235B, Q355B, Q355J2, 20#, S20C, S10C, S15C, ASTM A500 Gr.A/B/C/D, S235JR, S275JR, S355JR, Q195, Q345 |
| Standard | GB, ASTM A213, DIN EN 10217-1, ASTM A500, EN 10219, EN 10210, JIS G3466, AS1163 |
| Section Shape | Square |
| Size Range | 15×15 mm – 500×500 mm |
| Wall Thickness | 0.5 mm – 12 mm (up to 40 mm available) |
| Length | 5.8 m – 12 m (custom cut-to-length available) |
| Technique | Seamless (Hot Rolled) |
| Surface Treatment | Black / Hot Rolled / Galvanized (40–500 g/m²) / Painted |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures, construction frames, machinery, scaffolding, architectural facades, glass curtain walls, high-end steel structures |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, bridge support columns, scaffolding uprights |
| Architectural Facades | Glass curtain wall framing, exposed structural grids, right-angle facade elements |
| Machinery Manufacturing | Equipment base frames, conveyor support structures, hydraulic machine columns |
| Steel Structure Fabrication | Column-to-beam connections, truss chords, portal frame members |
Where Wall-Thickness Tolerance Decides Structural Acceptance
A ±1% tolerance on seamless square tubes keeps load calculations valid and avoids on-site rework.
Project engineers dimension steel frames around guaranteed section properties. When wall thickness drifts beyond tolerance — especially on heavy-wall Q355B tubes above 10 mm — the moment of inertia shifts, bolt-hole alignment fails, and third-party inspectors flag the batch. I have seen entire container loads of 200×200×10 mm seamless square tubes rejected at a Middle Eastern site because the actual wall measured 8.8 mm on the bottom layer, pushing sections outside EN 10219 limits [NEED_CITE: EN 10219 cold-formed and hot-formed hollow section dimensional tolerance requirements]. Sourcing a Q235B Q355B Seamless Square Steel Tube Supplier who controls tolerance at the rolling stage — not just at final inspection — eliminates that risk before the tube leaves Jinan.
Matching Seamless Square Sections to Structural and Architectural Demands
Hot-rolled seamless square tubes in Q235B and Q355B carry axial and bending loads without the weld-seam vulnerability that ERW sections introduce at corner zones. For glass curtain wall framing, the uniform corner geometry of seamless tubes — available from 15×15 mm up to 500×500 mm — gives clean sight-lines and predictable bolt-hole positioning. On heavy industrial frames where Q355B tubes run 12 mm wall and 12 m length, the seamless process maintains consistent mechanical properties across the full cross-section, which matters when fabricators weld moment connections without pre-heating.
Engineering Compliance Across GB, EN, and ASTM Frameworks
Structural engineers specifying Q355B under GB often need equivalence to S355JR under EN 10219 or ASTM A500 Gr.C for projects entering EU or North American markets. The seamless hot-rolled process meets EN 10210 requirements for structural hollow sections, and our in-house physical and chemical laboratory issues mill test certificates aligned with EN 10204 3.1 format [NEED_CITE: steel grade equivalence mapping between GB Q355B, EN S355JR, and ASTM A500 Gr.C]. For corrosive environments — coastal facades, industrial plants, agricultural structures — galvanized coating at 40–500 g/m² extends service life without changing the base section properties. Custom cut-to-length between 5.8 m and 12 m reduces on-site welding and fits directly into erection sequences.
Steel Grade Selection and Seamless Process Fundamentals
Q235B serves general structural work where moderate strength suffices — scaffolding, light frames, non-critical bracing. Q355B steps up yield capacity for primary load-bearing members in buildings and bridges, while Q355J2 adds low-temperature impact toughness for cold-climate or dynamic-loading applications. The seamless hot-rolled route starts from solid round billet, pierces, and elongates through a mandrel mill — no weld seam means no heat-affected zone at the corners, which is where rectangular and square tubes experience the highest stress concentration. This matters for Q235B Q355B Seamless Square Steel Tube orders going into machinery frames that see vibration, or facade structures where corner appearance must stay sharp after galvanizing. Surface treatment choice follows environment: black or hot-rolled for indoor or painted-over work, galvanized for outdoor exposure, and painted when color matching or additional chemical resistance is required.
Hidden Costs When Material Certification Falls Short
Ordering Q355B tubes without verified EN 10204 3.1 certificates risks customs rejection in EU ports — CE marking under EN 10210/EN 10219 is mandatory for structural hollow sections entering the European Economic Area [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 10210]. Beyond customs, material mismatches between heat-number traceability and physical delivery force re-testing at destination, delaying erection schedules. When wall thickness runs negative beyond tolerance, the theoretical weight invoicing model works against the buyer: you pay for section properties you do not receive, and structural engineers must recalculate or reject.
Why Project Procurement Teams Source Q235B Q355B Seamless Square Steel Tube Here
Our Jinan mill runs three dedicated seamless lines covering over 2,800 specifications — including off-standard sizes that trading companies cannot source from stock. Every Q235B Q355B Seamless Square Steel Tube ships with certificates from our in-house laboratory, and we hold CE certification under EN 10210 and EN 10219, ISO 9001:2015, and Singapore FPC for regulated markets. We pioneered sharp-corner rectangular tube technology in China with 41 invention patents, and that corner-control expertise transfers to our seamless square production — giving tighter dimensional consistency at the 40mm wall-thickness end of the range. For export orders, I personally review every container loading plan: bottom-layer dunnage, inter-layer separators, and inflatable bags at the doors prevent the crushing damage I watched destroy a 22-ton Dubai shipment years ago.
Documentation & Compliance
- Mill test certificate documenting Q235B and Q355B chemical composition and mechanical properties per GB/T 1591 and EN 10204 3.1 format
- CE certificate under EN 10210 and EN 10219 for structural hollow sections entering EU and EEA markets
- ISO 9001:2015 quality management system certificate covering seamless square tube production and testing
- SGS or BV third-party inspection report available before shipment for project-specific compliance verification
- Full heat-number traceability from billet to finished Q235B Q355B Seamless Square Steel Tube, linked to mill test certificate
- Export customs documents including packing list, bill of lading, and certificate of origin aligned with destination-country requirements
Packaging, Loading & Delivery
- Q235B and Q355B seamless square tubes bundled with steel strips and seaworthy packaging, sized to fit 20ft and 40ft containers without overhang
- Galvanized square tubes wrapped with edge protectors and moisture-resistant paper to preserve the 40–500 g/m² zinc coating during ocean transit
- Container loading optimized for 5.8 m and 12 m lengths with bottom dunnage and inter-layer wooden separators to prevent surface scratching and corner deformation
- Custom cut-to-length service available within the 5.8 m to 12 m range, with each piece marked by heat number, steel grade, and dimension
- FOB Jinan/Qingdao, CIF destination port, or DDP door-to-door delivery arranged based on project timeline and incoterm preference
- Every container shipped with a loading diagram and photo record, so site teams know exactly what to expect at unloading
Getting Your Q235B Q355B Seamless Square Steel Tube Quote Started
Send your dimension schedule — outer side length, wall thickness, length, steel grade, surface treatment, and total tonnage — along with the destination port. We return a detailed quotation with unit pricing, production lead time, and shipping terms within 12 hours, together with sample mill test certificates for your engineer’s review.
Request Your Seamless Square Tube Quotation and Mill Test Certificate
Submit your specification list and destination details to receive pricing, certification documents, and container loading plans.
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Frequently Asked Questions
Q: How do Q235B and Q355B map to ASTM A500 and EN 10219 steel grades?
A: Q235B generally corresponds to ASTM A500 Gr.A and EN S235JR in yield strength range, while Q355B aligns with ASTM A500 Gr.B/Gr.C and EN S355JR. We provide cross-standard equivalence documentation with every Q235B Q355B Seamless Square Steel Tube shipment so your engineer can verify compliance without additional testing.
Q: Can you provide EN 10204 3.1 mill test certificates and arrange third-party inspection?
A: Yes. Our in-house physical and chemical laboratory issues EN 10204 3.1 certificates for every heat, and we coordinate SGS or BV third-party inspection at the mill before shipment for projects requiring independent verification.
Q: What is the MOQ for non-standard dimensions and cut-to-length orders?
A: The standard MOQ is 1 Ton. For custom non-standard sizes outside our regular 15×15 mm to 500×500 mm range or specific cut-to-length requirements, we evaluate feasibility based on the dimension and tonnage — contact us with your schedule for a tailored assessment.
Q: When should I choose galvanized over hot-rolled or painted surface treatment?
A: Galvanized coating at 40–500 g/m² suits outdoor or corrosive environments — coastal construction, industrial plants, agricultural structures — where long-term corrosion resistance matters without ongoing maintenance. Hot-rolled or black finish works for indoor applications or projects where the tube will be painted on-site. Painted finish is selected when color matching or specific chemical resistance is required.
Q: How do you prevent tube damage during container loading for export?
A: We use bottom dunnage, inter-layer wooden separators, and inflatable bags at container doors. Every container ships with a loading plan and photo record. This approach came from watching a 22-ton shipment of heavy-wall tubes arrive crushed at destination because the previous supplier skipped bottom padding — we now treat loading as critically as production.
