Description
Direct Mill Supply for Q235B Q345B Welded Square Steel Tube — 2,800+ cross-section specifications produced on three in-house ERW and cold-forming lines, shipped with EN 10219 / EN 10210 mill test certificates to 50+ countries.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q345B Welded Square Steel Tube |
| Product Type | Welded Square and Rectangular Steel Tube |
| Steel Grade | Q195, Q235, Q235B, Q345, Q345B, SS400, ASTM A53 (A/B), ASTM A106 (B/C), S235JR, S275JR, S355J2 |
| Standard | ASTM A53, ASTM A106, API 5L, EN 10219, EN 10210, GB/T 6728, JIS G3466 |
| Section Shape | Square / Rectangular |
| Size Range | 15mm × 15mm – 800mm × 800mm |
| Wall Thickness | 1mm – 50mm (customized available) |
| Length | 6000mm, 12000mm (customized available) |
| Technique | ERW / Hot Rolled / Cold Rolled |
| Surface Treatment | Black Painted, Varnished, Hot-Dip Galvanized, Electro-Galvanized, 3LPE/3LPP Coated, Oiled |
| Tolerance | ±1% |
| Ends | Plain / Beveled / Threaded |
| Application | Steel structures, construction frameworks, scaffolding, machinery, oil & gas pipeline, automotive chassis, shipbuilding, hydraulic and pneumatic systems |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & EPC | Building frames, scaffolding uprights, curtain wall mullions, bridge handrails |
| Machinery Manufacturing | Hydraulic cylinder housings, pneumatic actuator frames, conveyor support structures |
| Oil & Gas / Shipbuilding | Pipeline transmission sleeves, offshore platform bracing, marine piping supports |
| Steel Structure Fabrication | Portal frame columns, truss chords, base plate connectors |
What Wall-Thickness Tolerance Costs on a Q235B Q345B Welded Square Steel Tube Order
A ±1% tolerance on a 50mm-wall Q345B tube is the difference between passing structural inspection and scrapping a 40-ton container at the port.
Procurement teams sourcing welded square tubes for load-bearing frames routinely discover that a 3% negative tolerance deviation — common among traders consolidating mixed-mill stock — pushes the actual section modulus below the engineer’s calculated safety margin. The result is not a paperwork issue but a physical one: beam deflection under design load, weld joint misalignment at moment connections, and rejection during third-party site inspection. [NEED_CITE: EN 10219 cold-formed structural hollow section dimensional tolerance requirements] When the mill test certificate lists Q345B but the delivered chemistry matches a lower-grade billet, the entire batch must be re-graded or scrapped, adding weeks to the project schedule.
How Q345B Section Geometry Matches Structural Frame Loads
A Q235B Q345B welded square steel tube with 800mm × 800mm outer dimension and 40mm wall thickness delivers the section modulus required for portal frame columns in industrial warehouses and high-rise transfer structures. The ERW welding process produces a continuous longitudinal seam that, when combined with cold-forming sizing passes, maintains flat-to-flat dimensional consistency across the full 12-meter length — critical when fabricators are drilling bolt-hole patterns at 300mm centers. For corrosive environments such as coastal infrastructure or chemical plant pipe racks, hot-dip galvanized Q235B Q345B welded square steel tube surfaces provide zinc coating thickness sufficient for 20+ year service life without field repainting.
Engineering Compliance Across EN, ASTM, and GB Frameworks
Structural engineers specifying welded square tubes for EU-funded infrastructure projects require CE marking under EN 10219 (cold-formed) or EN 10210 (hot-formed) — without this certification, customs authorities in Rotterdam, Hamburg, or Valencia will hold the shipment regardless of mill test chemistry. [NEED_CITE: CE marking requirements for structural steel hollow sections under EU Construction Products Regulation] For North American projects, ASTM A53 Grade B or A500 Grade C equivalence must be documented on the mill test certificate; the same Q345B chemistry satisfies ASTM A572 Grade 50 requirements when properly cross-referenced. Wall thickness selection directly affects compliance: a 12mm-wall S355J2 tube meets EN 1993-1-1 buckling resistance for mid-rise bracing, while a 6mm-wall Q235B tube is limited to non-structural cladding supports.
Steel Grade Selection: Q-Series, S-Series, and ASTM Equivalence
The Q235B / Q345B designation follows China’s GB/T 700 and GB/T 1591 standards, where the number indicates minimum yield strength in MPa — Q235B yields at 235 MPa, Q345B at 345 MPa. The European EN 10025 S-series (S235JR, S275JR, S355J2) follows the same logic, with the suffix indicating impact test temperature: JR for +20°C, J2 for -20°C. ASTM A53 Grade B and A36 occupy a similar strength band but use different chemistry limits, particularly for carbon and manganese content. [NEED_CITE: steel grade equivalence tables between GB, EN, and ASTM structural steel standards] For a Q235B Q345B welded square steel tube order targeting both domestic Chinese projects and EU export, specifying S235JR / S355J2 on the purchase order ensures the mill produces to EN chemistry limits while maintaining GB mechanical properties — avoiding the need for dual certification.
Hidden Costs of Specifying the Wrong Grade or Tolerance
Ordering Q235B when the structural drawing calls for Q345B reduces the load-bearing capacity by roughly 30% — a discrepancy that site inspectors will catch during ultrasonic thickness testing, triggering full-batch rejection. Similarly, accepting a “standard tolerance” tube when the engineering specification demands ±1% means the fabricator must machine every piece to achieve the required fit-up, adding labor costs that exceed the original material savings. Certification gaps create the most expensive delays: a container of welded square tubes arriving in the EU without EN 10219 mill test certificates will be held at the port until the importer can arrange retroactive testing — typically 3-4 weeks of demurrage charges plus the cost of flying in a third-party inspector. [NEED_CITE: port demurrage costs for non-compliant steel imports]
Why Procurement Teams Source Q235B Q345B Welded Square Steel Tube from Xin Jiyuan
Every Q235B Q345B welded square steel tube leaving our Jinan facility passes through an in-house physical and chemical laboratory before shipment — the same lab that helped us draft China’s cold-formed steel industry standards in 2018. We hold 41 invention patents, including the original sharp-corner rectangular tube technology that eliminates the rounded-corner aesthetic compromise architects face with conventional ERW tubes. Our three production lines cover 2,800+ specifications from 15mm × 15mm × 1mm up to 800mm × 800mm × 50mm wall thickness, meaning a single purchase order can consolidate building frame columns, scaffolding uprights, and machinery chassis tubes without splitting across multiple suppliers. Full CE certification under EN 10219 and EN 10210, ISO 9001:2015 quality management, and Singapore FPC approval ensure customs clearance across the EU, Middle East, and Southeast Asia. Professional container loading with anti-damage measures — including edge protectors for galvanized surfaces and interlocking bundle stacking for 12-meter lengths — prevents the bending and surface scratches that trigger destination rejection.
Documentation & Compliance
- Mill test certificate documenting Q235B / Q345B chemical composition (C, Mn, Si, P, S) and yield strength per GB/T 700 / GB/T 1591, with heat number traceability
- CE certificate confirming EN 10219 cold-formed hollow section compliance for S235JR / S355J2 grades exported to EU member states
- ISO 9001:2015 quality management system certificate covering the full production process from raw material incoming inspection to final dimensional testing
- SGS or BV third-party inspection report available upon request, verifying wall thickness tolerance, surface coating thickness, and weld seam integrity
- Material traceability report linking each bundle to its heat number, production date, and laboratory test results
- Customs documentation including packing list, bill of lading, certificate of origin, and fumigation certificate for wooden packaging
Packaging, Loading & Delivery
- Q235B / Q345B welded square steel tubes bundled with high-tensile steel strips at 1.5-meter intervals, wrapped in waterproof kraft paper for ocean transit
- Hot-dip galvanized tube bundles fitted with rubber edge protectors to preserve zinc coating integrity during container stuffing and unloading
- 12-meter length tubes loaded in interlocking pattern within 40ft open-top containers, maximizing payload while preventing longitudinal shifting
- Custom cut-to-length service available for 6000mm / 12000mm standard lengths, with cut ends deburred and capped to prevent internal corrosion
- Heat number and steel grade stenciled on each bundle tag, matching mill test certificate documentation for site verification
- FOB Qingdao / Tianjin ports, with CIF and DDP options to major construction hubs in the EU, Middle East, and Southeast Asia
Request a Quotation with Mill Test Certificate Preview
Submit your Q235B Q345B welded square steel tube specification — including outer dimension, wall thickness, steel grade, surface treatment, quantity, and destination port — and receive a detailed quotation within 12 hours, complete with a sample mill test certificate format and third-party inspection options. For non-standard dimensions outside our 2,800+ specification range, our engineering team will provide a custom production feasibility assessment and lead time estimate.
Get Your Q235B Q345B Welded Square Steel Tube Quote
Send your specification to admin@sdxjypipe.com or WhatsApp +86 188 5315 7756 to receive pricing, certification documentation, and production lead time confirmation.
Frequently Asked Questions
Q: How do Q235B and Q345B grades correspond to European S235JR and S355J2 standards?
A: Q235B and S235JR share similar yield strength (235 MPa minimum) and chemistry limits, making them functionally equivalent for most structural applications. Q345B corresponds to S355J2 with 345 MPa minimum yield strength, though the J2 suffix indicates impact testing at -20°C — a requirement for cold-climate projects that Q345B’s standard GB/T 1591 specification does not automatically include.
Q: Can you produce non-standard dimensions outside the 15mm–800mm range?
A: Yes, our three production lines support custom non-standard sizes beyond the standard 2,800+ specification catalog. Custom dimensions typically require a minimum order quantity and extended production lead time; submit your drawing or dimensional requirement for a feasibility assessment.
Q: What is the difference between hot-dip galvanized and electro-galvanized surface treatment for welded square tubes?
A: Hot-dip galvanizing immerses the finished tube in molten zinc, producing a coating thickness of 45-85 micrometers suitable for outdoor and corrosive environments. Electro-galvanizing applies a thinner zinc layer (5-25 micrometers) through electrolytic deposition, offering a smoother finish for indoor architectural applications where appearance matters more than long-term corrosion resistance.
Q: Do your welded square tubes carry CE marking for European construction projects?
A: Yes, all Q235B Q345B welded square steel tubes exported to the EU are produced under our CE-certified quality system conforming to EN 10219 (cold-formed) and EN 10210 (hot-formed) standards. The mill test certificate and Declaration of Performance accompany every shipment for customs clearance and site inspection compliance.
Q: How are 12-meter welded square tubes loaded to prevent bending during ocean transit?
A: Tubes are bundled with high-tensile steel strips, wrapped in waterproof paper, and loaded in an interlocking pattern within the container. Rubber edge protectors are placed at contact points for galvanized surfaces, and void-fillers secure the load against longitudinal shifting during vessel movement.
