Description
Factory-Direct Welded Square Steel Tube Supply — All Q235, Q345, and S355 RHS produced in-house from raw slab to finished section, eliminating third-party material gaps.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345 Welded Square Steel Tube |
| Product Type | Welded Square Steel Tube (RHS/SHS) |
| Steel Grade | Q195, Q215, Q235, Q345, GR.A, GR.B, S235, S355 |
| Standard | ASTM, EN |
| Section Shape | Square |
| Size Range | 10×10 mm – 600×600 mm |
| Wall Thickness | 0.8 – 30 mm |
| Length | 5.7 m / 6 m |
| Technique | Welded ERW |
| Surface Treatment | Bare / Pre-galvanized / Hot-dipped galvanized / Oiled |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures / Construction frames / Machinery / Scaffolding / Fluid transport / Structure pipe |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Industrial Construction | Portal frame columns, roof truss chords, warehouse mezzanine beams |
| Infrastructure | Highway sound barrier posts, bridge handrail supports, lighting pole bases |
| Machinery Manufacturing | Equipment skid frames, conveyor support structures, crane boom sections |
| Temporary Works | Scaffolding verticals, shoring props, formwork tie members |
Where Negative Tolerance Turns a Budget Order into a Site Rejection
Dimensional accuracy on welded square steel tube determines whether your structure passes inspection or gets torn down.
I once watched a container of 25×50 rectangular tubes get rejected at destination because wall thickness drifted past the allowable negative tolerance. The buyer’s third-party inspector pulled random pieces, measured them, and the entire lot failed. That is not a material cost problem — it is a demolition problem. When sourcing EN standard welded square steel tube from overseas, fragmented suppliers who buy black pipe from random mills and fabricate in separate workshops create traceability gaps that no amount of paperwork can fix [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements].
How Dimensional Range Matches Structural Frame Requirements
The 10×10 to 600×600 mm size range with 0.8–30 mm wall thickness covers everything from light gauge scaffolding uprights to heavy industrial column sections. For EPC warehouse projects, S355 grade welded square steel tube in the 150×150 to 300×300 mm range with 8–12 mm walls provides the section modulus needed for portal frame rafter connections while keeping tonnage manageable for container shipping. The ±1% tolerance holds across the full range because ERW welding with certified WPS procedures controls distortion during forming.
Engineering Compliance and Certification Pathways
Structural frames for EU-bound projects require CE marking under EN 10210 (hot-finished) or EN 10219 (cold-formed) — and the welded square steel tube must carry Factory Production Control certification from a notified body [NEED_CITE: CE marking requirements for structural hollow sections under CPR Regulation]. For Middle East and Southeast Asian infrastructure, ASTM A500 Grade B or C specifications dominate, requiring different chemistry limits than EN S-series grades. Our in-house laboratory handles PMI testing, tensile sampling, and Charpy impact testing per heat number, so the mill test certificate reflects actual production data rather than generic mill templates.
Steel Grade Selection and ERW Welding Fundamentals
Q235 remains the default for domestic Chinese projects and cost-sensitive export work where yield strength above 235 MPa suffices. S235JR and S355JR serve European-spec jobs with guaranteed impact energy at sub-zero temperatures. The ERW welding process forms the square section from coiled strip, welding the longitudinal seam under continuous flux protection — this produces a consistent weld zone that passes ultrasonic inspection when procedure qualification records are followed. Hot-dipped galvanizing adds 60–80 μm zinc coating for outdoor exposure, while pre-galvanized (zinc-coated strip before forming) suits indoor machinery frames where appearance matters more than corrosion resistance.
The Hidden Cost of Unverified Material Sources
Buying welded square steel tube from traders who cannot show heat-level traceability means you accept unknown chemistry. S355 specified but Q235 delivered creates a yield strength shortfall that only shows up when the structure deflects under load. EN 10204 3.2 certificates with third-party witness testing close this gap — but only if the fabricator controls the entire chain from slab to finished tube [NEED_CITE: material traceability requirements under EN 10204 Type 3.2 certification].
Why Vertically Integrated Production Eliminates Procurement Risk
Our steel mill produces the hot-rolled coil that feeds our tube mill’s ERW line — no external black pipe purchases, no chemistry surprises. The fabrication workshop downstream handles cutting, drilling, and welding connections using the same material, so shop drawing coordination stays within one quality system. We hold 2,800+ specifications in stock across Q235, Q345, and S-series grades, meaning standard sizes ship within typical production lead times while custom dimensions follow engineering approval. CE certification under EN 10219, ISO 9001 registration, and acceptance of SGS/BV/TÜV third-party inspection provide the documentation trail that customs authorities and project owners demand.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition and mechanical properties per GB/T 700, or S355JR per EN 10025-2, with heat number traceability
- CE certificate confirming compliance with EN 10219 cold-formed welded structural hollow sections for EU market entry
- ISO 9001 quality management system certificate covering steel tube production and fabrication processes
- SGS or BV third-party inspection report verifying dimensional accuracy, weld quality, and coating thickness per purchase specification
- Material traceability report linking each bundle to heat number, chemistry analysis, and mechanical test results
- Export documentation including packing list, bill of lading, and certificate of origin for customs clearance
Packaging, Loading & Delivery
- Bare welded square steel tube bundled with steel strips and edge protectors to prevent coating damage during ocean transit
- Hot-dipped galvanized RHS wrapped with waterproof paper and plastic sleeves to preserve zinc coating integrity
- 6-meter lengths loaded in 20ft or 40ft containers with optimized nesting for 150×150 to 300×300 mm sections
- Pre-galvanized tubes marked with heat number and steel grade stenciled on each piece for site identification
- FOB Jinan/Qingdao port or CIF/DDP delivery to project site with full export documentation package
- Custom cutting to project-specific lengths available upon engineering drawing approval
How to Initiate a Project-Specific Inquiry
Submit your engineering drawings (PDF/DWG), steel grade specification, quantity, and destination port. We return a detailed quotation covering material, fabrication, coating, packing, and shipping within 24 hours, along with shop drawing timelines and production scheduling. For EN standard welded square steel tube projects requiring CE certification or third-party inspection witness, confirm these requirements upfront so we allocate the appropriate quality control resources.
Frequently Asked Questions
Q: What is the difference between Q235, S235JR, and ASTM A36 for welded square steel tube?
A: Q235 is the Chinese national standard grade with minimum yield strength of 235 MPa. S235JR is the European EN standard equivalent with guaranteed impact energy at room temperature. ASTM A36 serves North American specifications. All three are interchangeable for general structural applications, but project specifications dictate which chemistry and testing standards apply.
Q: Can you provide EN 10204 3.2 certificates with third-party witness?
A: Yes. We arrange SGS, BV, or TÜV inspection witness for tensile testing, chemistry analysis, and dimensional verification. The EN 10204 3.2 certificate requires independent third-party validation of test results, which we coordinate at our in-house laboratory.
Q: What is the minimum order quantity for non-standard dimensions?
A: Standard sizes (10×10 to 600×600 mm, 0.8–30 mm wall) have 1 ton MOQ. Non-standard dimensions or custom lengths require engineering review and may carry higher MOQ depending on mill setup requirements.
Q: How do you handle negative tolerance on wall thickness?
A: We maintain ±1% tolerance across the full size range. Wall thickness is measured at four points per piece using ultrasonic gauges. If your project requires zero negative tolerance or tighter controls, specify this in the purchase order and we adjust production parameters accordingly.
Q: What surface treatment works best for outdoor structural frames?
A: Hot-dipped galvanizing provides 60–80 μm zinc coating for long-term corrosion protection in outdoor environments. Pre-galvanized (zinc-coated strip before forming) suits indoor applications. Bare tubes require site-applied painting or coating per project specification.
[Request Quotation with Mill Test Certificate]
Send your project specifications, steel grade requirements, and destination port to receive a detailed quotation with material certification documentation.
Contact:
- Tel: +86 531 8573 6315
- Mobile/WhatsApp/WeChat: +86 188 5315 7756
- Email: admin@xjystructure.com
