Description
Factory-direct pricing, no middlemen markup — Every Q235 Q345 welded square steel tube rolls off our own ERW lines in Jinan, shipped with full mill test traceability to your port.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345 Welded Square Steel Tube |
| Product Type | Welded Square Steel Tube (ERW) |
| Steel Grade | Q195, Q215, Q235, Q345, S235, S355, GR.A, GR.B |
| Standard | ASTM, EN (as indicated in title) |
| Section Shape | Square |
| Size Range | 10×10 – 600×600 mm |
| Wall Thickness | 0.8 – 30 mm |
| Length | 5.7m / 6m |
| Technique | Welded ERW |
| Surface Treatment | Bare / Pre-galvanized / Hot-dipped galvanized / Oiled |
| Tolerance | ±1% |
| Ends | Plain |
| Invoicing | By Theoretical Weight |
| Application | Structure Pipe / Steel structures / Construction frames / Machinery / Scaffolding |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors | Industrial warehouse frames, plant support structures, pipe rack systems |
| Construction Companies | High-rise building columns, bridge support piers, scaffolding uprights |
| Machinery Manufacturers | Equipment base frames, conveyor support structures, hydraulic machine housings |
| Infrastructure Developers | Sound barrier posts, solar panel mounting structures, fencing systems |
What Happens When Wall Thickness Tolerance Drifts on a Structural Frame
A ±1% tolerance on a 30mm wall Q345 square tube means the difference between passing structural inspection and tearing down a warehouse frame.
I have seen EPC procurement teams sign off on a container of welded square tubes only to discover at the fabrication yard that the wall thickness measured 0.6mm below nominal on the thin side. The steel grade stamp said Q345, but the load-bearing calculation assumed the full 30mm section. When the structural engineer recalculated with actual measured dimensions, the safety factor dropped below the EN 1993 threshold. The entire batch became scrap — not because the steel was wrong, but because the tolerance was loose. [NEED_CITE: EN 10219 cold-formed welded structural hollow sections tolerance requirements] Fragmented sourcing makes this worse: you buy tubes from one supplier, plates from another, and nobody takes responsibility for the dimensional chain.
How ERW Square Tubes Match Structural Frame Load Requirements
A Q235 Q345 welded square steel tube in the 100×100 to 400×400mm range with 4–16mm wall thickness handles the majority of medium-duty structural frame applications — warehouse portals, mezzanine supports, and machinery bases. The ERW welding process produces a continuous longitudinal seam that, when properly controlled, delivers uniform strength around the entire perimeter. For corrosion-prone environments such as coastal construction sites or chemical plant frames, hot-dipped galvanized surface treatment extends service life without additional field coating. Our in-house laboratory tests every heat number against the chemical composition and mechanical requirements before the tube leaves the mill, so the Q235 Q345 welded square steel tube you receive matches the grade on the mill test certificate.
Engineering Compliance: From EN 10219 to Site Fabrication
Structural frames designed under EN 1993 require hollow sections that conform to EN 10219 for cold-formed welded tubes or EN 10210 for seamless and welded sections. The Q235 Q345 welded square steel tube we supply meets these dimensional and material standards, with CE certification covering the EN 10210/10219 scope for EU market entry. For projects in North America, the same tube dimensions can be supplied in ASTM A500 Grade B or Grade C equivalents. Wall thickness selection directly affects the section modulus and moment of inertia — a 200×200×8 tube carries significantly less bending moment than a 200×200×12, and the choice must align with the structural engineer’s calculation. [NEED_CITE: steel grade equivalence between Chinese Q-series and European S-series standards] Plain ends allow on-site welding, drilling, and bolted connection without additional end preparation, reducing fabrication time at the erection stage.
Understanding Q235 vs Q345 and the ERW Welding Process
Q235 and Q345 represent two tiers in the Chinese structural steel grading system. Q235 offers adequate strength for non-critical framing, scaffolding, and general fabrication where high load capacity is not required. Q345 delivers higher yield strength, making it the default choice for primary structural members, crane runway beams, and heavy machinery frames. When the project specification calls for European grades, S235 and S355 map closely to Q235 and Q345 respectively in terms of minimum yield strength classification. [NEED_CITE: comparison of yield strength classes across GB, EN, and ASTM steel standards]
The ERW (Electric Resistance Welding) process forms the square section by cold-rolling a steel strip into shape and fusing the seam through electrical resistance heat — no filler metal, no slag. This produces a clean, uniform weld zone suitable for subsequent galvanizing or painting. For wall thicknesses up to 30mm across the 10×10 to 600×600mm range, ERW provides a cost-effective alternative to seamless tube while maintaining structural integrity for non-high-pressure applications. Surface treatment selection depends on the service environment: bare tubes with oil coating suit indoor fabrication, pre-galvanized tubes offer moderate corrosion protection for sheltered structures, and hot-dipped galvanized tubes withstand outdoor exposure in industrial and infrastructure projects.
The Hidden Cost of Accepting Unverified Mill Test Certificates
A mill test certificate that cannot be traced back to a specific heat number is a liability, not a document. When customs authorities in the EU or Middle East request proof of EN 10219 compliance and the certificate lacks traceable chemistry and mechanical test data, the shipment gets held — sometimes for weeks. [NEED_CITE: customs documentation requirements for structural steel imports into EU member states] Worse, if a structural inspector discovers that the actual yield strength falls below the S355 minimum during on-site testing, the entire installation may need to be dismantled and replaced. The cost of re-procurement, demolition, and project delay dwarfs any initial savings from buying unverified material. Certification gaps do not just cause customs delays; they create structural safety risks that no amount of re-testing can fix after erection.
Why Procurement Teams Choose Our Mill for Welded Square Tubes
Every Q235 Q345 welded square steel tube ships from our own three production lines in Jinan — no trading company markup, no third-party warehouse handling. Our in-house physical and chemical laboratory tests incoming raw material, monitors the ERW welding process in real time, and performs final inspection on every bundle before release. The mill test certificate you receive documents the actual heat number, chemical composition, and mechanical test results for the specific tubes in your container. We hold CE certification under EN 10210/10219, ISO 9001:2015 registration, and third-party verification from SGS and BV — covering the documentation requirements for EU, North American, and Middle Eastern customs clearance. Our range covers over 2,800 specifications from 10×10 to 600×600mm with wall thickness up to 30mm, including non-standard sizes that other mills refuse to roll. For projects requiring sharp-corner rectangular tubes, our proprietary technology holds 41 patents and fills a gap that standard catalog suppliers cannot address. Professional loading plans optimize container utilization for mixed-size orders, and we coordinate FOB, CIF, and DDP shipments to 50+ countries with full tracking.
Documentation & Compliance
- Mill test certificate documenting Q235 or Q345 chemical composition and mechanical properties per heat number, issued from our in-house laboratory
- CE certificate covering EN 10210/10219 compliance for structural hollow sections entering EU member state markets
- ISO 9001:2015 quality management system certificate covering the full production process from raw material incoming to final shipment
- SGS or BV third-party inspection report available upon request, covering dimensional verification, surface quality, and weld integrity
- Material traceability report linking each bundle to its heat number, production date, and test batch for full audit chain
- Customs documentation package including packing list, bill of lading, and certificate of origin formatted for destination port requirements
Packaging, Loading & Delivery
- Q235 and Q345 welded square tubes bundled with galvanized steel strips at intervals matching the 5.7m and 6m standard lengths, preventing bundle shift during ocean transit
- Hot-dipped galvanized square tubes packed with edge protectors and moisture-resistant wrapping to preserve the zinc coating from white rust formation during container shipping
- Pre-galvanized and bare tubes coated with anti-rust oil before bundling, with steel grade and heat number stenciled on each bundle end for yard identification
- Mixed-size container loading plans optimized for 20ft and 40ft containers, nesting smaller square tubes inside larger sections to maximize payload per shipment
- Custom cut-to-length service available for 6m standard tubes, with cut ends deburred and marked per the project drawing before packaging
- FOB Jinan or Qingdao port for standard orders, with CIF and DDP options coordinated through our logistics team for door-to-door delivery to project sites across 50+ countries
How to Start Your Welded Square Tube Procurement
Send your specification list — including section size, wall thickness, steel grade, surface treatment, quantity, and destination port — and we return a detailed quotation within 12 hours covering unit price, production lead time, applicable certifications, and shipping terms. For non-standard dimensions outside the 10×10 to 600×600mm catalog range, we provide custom rolling feasibility confirmation and MOQ requirements. You receive the mill test certificate draft before production begins, so your quality team can verify the heat number traceability and grade compliance against your project specification.
Frequently Asked Questions
Q: What is the difference between Q235 and Q345 for structural applications?
A: Q235 provides adequate strength for secondary structures, scaffolding, and general fabrication. Q345 offers higher yield strength and is specified for primary structural members, heavy equipment frames, and load-bearing columns where higher moment capacity is required.
Q: Can you supply the Q235 Q345 welded square steel tube with EN 10219 certification for EU projects?
A: Yes. Our welded square tubes carry CE certification under EN 10210/10219. The mill test certificate documents chemical composition and mechanical properties per the EN standard, and we provide full customs documentation for EU port clearance.
Q: What surface treatment options are available for corrosion protection?
A: We supply bare tubes with anti-rust oil for indoor use, pre-galvanized tubes for sheltered outdoor applications, and hot-dipped galvanized tubes for full weather exposure in infrastructure and industrial environments.
Q: Do you offer non-standard sizes outside the 10×10 to 600×600mm range?
A: Yes. Beyond our standard catalog of over 2,800 specifications, we produce custom non-standard square and rectangular tubes to project drawings. MOQ for custom sizes depends on the section dimensions and rolling feasibility.
Q: How do you ensure material traceability for each shipment?
A: Every bundle is linked to a specific heat number. The mill test certificate documents the chemical composition and mechanical test results for that heat. Third-party inspection from SGS or BV is available to verify dimensional accuracy and material compliance before shipment.
Get Your Welded Square Tube Quotation with Full Mill Test Traceability
Submit your section size, wall thickness, steel grade, quantity, and destination port — we respond within 12 hours with pricing, certification details, and delivery terms.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjysteel.com
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjysteel.com
