Description
Factory-direct Q235B square tube pricing — ERW welded SHS from 19×19mm to 800×800mm shipped with original mill test certificates and third-party inspection options.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Q235B Square Steel Tube |
| Product Type | Welded Square Steel Tube (ERW / 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 (Electric Resistance Welded) |
| Surface Treatment | Black Painting / Galvanized / Varnish / Bare |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Construction structures / Building frames / Curtain wall supports / Structural frames / Machinery supports |
| MOQ | 5 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Steel structure frames for industrial warehouses, curtain wall support systems, scaffolding uprights |
| Machinery & Equipment | Machinery bases, conveyor support frames, equipment mounting structures |
| Commercial Building | Building column frames, mezzanine structures, facade support grids |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A 0.3mm wall deviation on a 4mm Q235B square tube shifts actual weight by over 7% — and triggers rejection at project inspection.
Structural engineers calculate load capacity based on theoretical weight. When wall thickness runs below tolerance, the moment of inertia drops, deflection increases, and the frame fails load testing. I watched a Dubai client lose three weeks of installation schedule because their 100×100×4mm batch arrived 0.6mm under spec — the SGS inspector flagged it at Jebel Ali port. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements]
Beyond the physical risk, missing mill test certificates or inconsistent steel grade markings cause customs holds in the EU and GCC. A container without proper EN 10219 documentation sits at the port while the project crane waits.
Matching Q235B ERW Square Tubes to Structural Load Requirements
Q235B carbon steel square tube delivers adequate yield capacity for non-critical structural frames, curtain wall supports, and machinery bases where extreme dynamic loading is absent. The ERW welding process produces a consistent longitudinal seam that maintains dimensional stability across 6m and 12m lengths — critical when columns must align within millimeter tolerance on-site. For corrosive environments such as coastal construction or chemical plant walkways, hot-dip galvanized coating extends service life without compromising the ±1% dimensional tolerance that structural drawings demand.
Engineering Compliance and Surface Protection Selection
Structural hollow sections conforming to EN 10219 require documented chemical composition and mechanical properties for CE marking in European markets. [NEED_CITE: EN 10219 cold-formed hollow section requirements] Q235B maps to S235JR under EN standards and roughly to ASTM A36, but project specifications must confirm equivalence before substitution. Black painted finish suits indoor structural frames; galvanized coating is mandatory for outdoor exposure or buried applications. Plain ends allow field welding or mechanical coupling per site connection design. Third-party inspection by SGS or BV verifies compliance before shipment — essential for projects requiring independent quality assurance.
Understanding Steel Grade Selection and ERW Welding Quality
Q235B belongs to China’s GB standard system, offering balanced strength and weldability for general structural use. When projects specify S235, S275, or S355, these European grades provide incrementally higher yield strength — S355 delivers roughly 50% more load capacity than Q235B, allowing smaller section sizes for the same structural demand. The ERW process fuses the longitudinal seam through electric resistance heating without filler metal, producing a weld zone with mechanical properties matching the base material when properly controlled. [NEED_CITE: steel grade equivalence between EN and ASTM standards] Wall thickness tolerance of ±1% ensures that theoretical weight calculations align with delivered product — a critical factor when procurement is priced by weight but structural integrity depends on actual cross-section dimensions.
Hidden Costs of Unverified Material and Tolerance Shortcuts
Purchasing Q235B carbon steel square tube without original mill test certificates risks material substitution — lower-grade steel relabeled as Q235B passes visual inspection but fails mechanical testing. Negative tolerance beyond ±1% reduces load capacity while the buyer pays for theoretical weight. Missing CE documentation blocks customs clearance in EU member states, triggering demurrage charges and project delays. [NEED_CITE: structural steel certification requirements for customs clearance] Rejection at site inspection forces return shipping or local replacement at multiples of the original material cost.
Why Project Buyers Source Q235B Square Tubes from Xin Jiyuan
Every Q235B carbon steel square tube leaving our Jinan facility undergoes three-stage inspection: dimensional check per bundle, weld seam visual examination, and surface treatment verification. Original mill test certificates document chemical composition and mechanical properties for each heat number — not generic certificates copied across batches. Our 2,800+ specification inventory covers 19×19mm through 800×800mm in wall thickness up to 30mm, enabling consolidated container loading when projects require multiple sizes in a single shipment. Factory-direct pricing eliminates trading margins; volume discount programs reward long-term procurement partnerships. CE certification under EN 10210 and EN 10219, combined with ISO 9001:2015 quality management, satisfies compliance requirements across European, Middle Eastern, and African markets. Professional export documentation and container loading optimization reduce port delays and maximize payload per shipment.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition and mechanical properties per GB/T 3091, traceable by heat number
- CE certificate confirming EN 10219 compliance for structural hollow sections exported to European markets
- ISO 9001:2015 quality management certificate covering ERW welding and dimensional inspection processes
- SGS or BV third-party inspection report available for projects requiring independent verification before shipment
- Material traceability documentation linking each bundle to heat number, production date, and test results
- Customs documents including packing list with actual weight, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Q235B square tubes bundled with steel strips at intervals matching 6m and 12m lengths, preventing deformation during ocean transit
- Galvanized surfaces protected with edge guards and interleaving materials to preserve zinc coating integrity
- Container loading plans optimized for mixed-size shipments, maximizing payload when 19×19mm through 400×400mm sections ship together
- Random length or cut-to-order 5.8m/6m/11.8m/12m available per project specification, reducing on-site cutting waste
- Heat number and steel grade marked on each bundle tag, enabling site identification and inspection traceability
- FOB Jinan/Qingdao or CIF destination port terms with door-to-door logistics coordination for landlocked project sites
Requesting Quotation and Technical Documentation
Submit your Q235B carbon steel square tube requirements including section size, wall thickness, total tonnage, surface treatment preference, and destination port. We respond within 12 hours with factory-direct pricing, production lead time, and available mill test certificate samples. For non-standard sizes outside 19×19mm to 800×800mm range or custom lengths, we provide fabrication feasibility assessment and tooling requirements.
Start Your Q235B Square Tube Procurement
Send specifications via email or WhatsApp to receive bulk pricing and compliance documentation within one business day.
Contact: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxinjiyuan.com
