Description
Direct Mill Supply — Full heat-number traceability from our own steel production lines to every Q235B square tube shipped.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Q235B Square Steel Tube |
| Product Type | Square Steel Tube / Square Hollow Section (SHS) |
| Steel Grade | Q235B, Gr.B, S235, S275, S355, STK400 |
| Standard | ASTM A500, ASTM A53, GB/T 3091 |
| Section Shape | Square |
| Size Range | 19mm×19mm – 800mm×800mm |
| Wall Thickness | 1 – 30 mm |
| Length | 5.8m / 6m / 11.8m / 12m / Random Length |
| Technique | ERW (Welded) |
| Surface Treatment | Black Painting / Galvanized / Varnish / Bare |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures / Construction frames / Building structures / Curtain wall systems / Support tubes / Machinery / Scaffolding |
| MOQ | 5 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Commercial & Industrial Construction | Building columns, roof trusses, warehouse portal frames, mezzanine support beams |
| Infrastructure & Civil Engineering | Bridge handrail posts, sound barrier frames, highway sign gantry structures |
| Curtain Wall & Facade Systems | Mullion tubes, perimeter framing, decorative exposed steel grids |
| Machinery & Equipment | Conveyor frame structures, equipment support bases, scaffolding uprights |
What Negative Tolerance Really Costs on a Q235B Carbon Steel Square Tube Order
A 0.8mm wall shortfall on a 100×100×4 tube means 18% less load-bearing metal than your engineer calculated.
I learned this the hard way. A warehouse project in Shandong ordered Q235B 100×100×4 — the mill certificate said 4.0mm wall, but calipers read 3.2mm across the entire lot. Third-party inspection rejected it. The project stalled for weeks while replacement material was sourced. The trader who sold us that batch had bought from an unknown mill with no audit trail. When a Q235B carbon steel square tube supplier sources raw coil from multiple unverified mills, dimensional consistency becomes a gamble you cannot afford on structural frames. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements]
How ERW Square Hollow Sections Match Structural Frame Demands
A Q235B carbon steel square tube in the 100×100 to 300×300mm range with 4–12mm wall thickness serves as primary load-bearing members in portal frames and mezzanine structures. The flat internal surfaces of square sections simplify bolted and welded connections to gusset plates and beam seats — no rotational alignment issues that round tubes create. Our vertically integrated production means the same quality system governs the raw steel chemistry and the ERW welding sequence, so weld seam integrity matches the parent metal. For projects requiring S355 or ASTM A500 Gr.B equivalence, we supply matching grades under the same traceability framework.
Engineering Compliance and Certification Pathways
Structural frames designed under EN 1993 require hollow sections conforming to EN 10219 for cold-formed welded profiles, while North American projects reference ASTM A500 for cold-formed carbon steel tubing. [NEED_CITE: steel grade equivalence between Q235B, S235JR, and ASTM A500 Gr.B] The Q235B carbon steel square tube we produce meets GB/T 3091 domestically and can be certified to EN 10219 or ASTM A500 with full mill test documentation. Surface treatment selection — hot-dip galvanized for outdoor exposure, black painted for indoor structural use, or bare for site-applied coating systems — must align with the project’s corrosion environment classification. CE marking per EN 10219 is mandatory for structural steel entering the European market, and our production holds this certification across the full size range.
Steel Grade Selection and ERW Welding Fundamentals
Q235B remains the workhorse grade for general structural applications in China and markets accepting GB standards — it offers adequate strength for non-heavy-load frames at competitive cost. For projects specifying European standards, S235 provides equivalent yield classification, while S275 and S355 step up progressively for heavier load paths such as crane-supporting beams or multi-story column stacks. STK400 serves Japanese-spec structural applications. The ERW welding process we use forms the tube by cold-rolling flat strip into square profile and welding the longitudinal seam through high-frequency electric resistance — this produces a clean, narrow weld zone suitable for structural loading without the heat-affected zone width of submerged arc welding. Wall thickness tolerance of ±1% ensures that theoretical weight calculations match actual delivered weight, preventing the cost overruns that come from receiving underweight material.
The Hidden Cost of Sourcing from Unverified Traders
Material certificates that cannot be traced to a specific heat number create liability gaps when structural inspectors request verification. A Q235B carbon steel square tube without proper EN 10204 3.1 certification will face rejection at European customs or fail third-party inspection on-site. [NEED_CITE: EN 10204 inspection document types for steel products] Negative tolerance abuse — where wall thickness consistently falls below nominal — reduces section modulus and load capacity below engineering design values, creating structural safety risks that only surface during loading or inspection. Rework, replacement shipments, and project delays dwarf any per-ton price savings from unverified sources.
Why Procurement Teams Choose Our Integrated Mill-to-Tube Supply Chain
Our own steel mill feeds raw coil directly into the tube production line, eliminating the sourcing gaps that occur when fabricators buy material from third-party traders. Every Q235B carbon steel square tube carries a heat number traceable to our production records — no chain of custody breaks. We hold over 2,800 specifications in stock across our size range, reducing lead times for urgent project requirements. Our in-house quality lab issues mill test certificates per EN 10204 3.1, and we accommodate third-party inspections from SGS, BV, and TUV on any order. CE marking per EN 10219 covers our full European export range, and our loading team specializes in oversized structural tube bundling for container and breakbulk shipment.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition and mechanical properties per GB/T 3091, with heat number traceability to our own steel production
- CE certificate per EN 10219 for cold-formed welded structural hollow sections, required for customs clearance across European Union member states
- ISO 9001 quality management system certificate covering the full production process from raw material incoming inspection to finished tube dispatch
- SGS or BV third-party inspection report available for dimensional verification, weld seam testing, and coating thickness measurement per project specification
- Material traceability report linking each bundle’s heat number to production date, coil origin, and test results
- Complete customs documentation package including packing list, bill of lading, and certificate of origin for destination-country import clearance
Packaging, Loading & Delivery
- Q235B square tubes bundled with galvanized steel strips at intervals matching the 6m and 12m standard lengths, with edge protectors preventing coating damage during transit
- Galvanized surface tubes wrapped in waterproof paper and loaded with wooden spacers to preserve zinc coating integrity during ocean freight
- Small-section tubes (19×19 to 100×100mm) container-loaded in nested bundles optimizing 20ft and 40ft GP capacity; large-section tubes (400×400 and above) shipped via breakbulk or flat rack
- Random length and cut-to-order lengths available per project requirement, with cut ends deburred and protected against corrosion
- Each bundle marked with heat number, steel grade Q235B, size specification, and production batch for site identification and inspection traceability
- FOB Jinan/Qingdao, CIF, and DDP delivery terms available with professional oversized cargo loading plans
Start Your Procurement with Drawings and Specifications
Share your project drawings, required steel grade, size specifications, quantity, and destination port — we respond within 24 hours with pricing, mill test certificate samples, and a production timeline. For non-standard sizes or custom lengths outside our listed range, our engineering team reviews feasibility and provides a fabrication assessment. Confirm your certification requirements — CE marking, third-party inspection, or specific test standards — so we include all documentation in the initial quotation.
Frequently Asked Questions
Q: How does Q235B compare to S235JR and ASTM A500 Gr.B?
A: Q235B and S235JR share similar yield strength classifications under their respective Chinese GB and European EN standards. ASTM A500 Gr.B is the North American equivalent for cold-formed carbon steel structural tubing. We supply all three grades and can provide cross-reference documentation for projects requiring grade equivalence verification.
Q: Can you provide EN 10204 3.1 mill test certificates with heat number traceability?
A: Yes. Every Q235B carbon steel square tube we produce carries a mill test certificate per EN 10204 3.1, documenting chemical composition and mechanical properties. The heat number on each bundle traces back to our own steel production records, ensuring full material chain traceability.
Q: What is the MOQ and can you accommodate non-standard sizes?
A: Our minimum order quantity is 5 tons. For non-standard sizes outside the 19×19mm to 800×800mm range or custom wall thicknesses, our engineering team reviews drawing specifications and provides a feasibility assessment with production timeline.
Q: Which surface treatment should I specify for my project environment?
A: Hot-dip galvanized is recommended for outdoor or high-humidity environments requiring long-term corrosion protection. Black painting suits indoor structural applications where aesthetics and moderate protection are needed. Bare tubes are specified when the project applies its own coating system on-site. We advise based on your corrosion environment classification.
Q: Do you handle export documentation and CE marking for European projects?
A: Yes. We provide CE marking per EN 10219 for all structural hollow sections entering the EU market, along with complete customs documentation including packing list, bill of lading, certificate of origin, and third-party inspection reports from SGS or BV upon request.
Get Your Q235B Carbon Steel Square Tube Quotation with Full Mill Certification
Submit your project specifications, steel grade, size requirements, and destination port to receive pricing and mill test certificate samples within 24 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.xjystructure.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@xjystructure.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
