Q235 Q345 Welded Square Rectangular Steel Tube Supplier

Description

Gate Check

identifier: Q235/Q345 Welded Square and Rectangular Steel Tube — not null. Proceed.

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Direct mill supply, no trading markup — Every Q235 Q345 welded square and rectangular steel tube ships from our own ERW line with heat-number traceability back to the slab.

Technical Specifications

Application Suitability

What Negative Tolerance Really Costs on a 300×300 Frame Order

A ±1% wall-thickness tolerance sounds tight on paper — until the third-party inspector pulls the calipers at the port.

When overseas buyers source a Q235 Q345 welded square and rectangular steel tube for structural frames, the invoice says theoretical weight, but the acceptance criteria demand actual dimensional compliance. I once watched a warehouse project in Southeast Asia halt for two weeks because two container-loads of 300×300 sections arrived with wall thickness measuring below the contract minimum — the fabricator had pushed negative tolerance to the edge, and the client’s engineer refused to sign off. [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed hollow sections] The rework cost — air-freight replacement, idle crane crews, rescheduled erection — dwarfed any per-tonne saving the original supplier had offered. For project buyers, the real question is not whether the tube meets the standard on the mill test certificate, but whether every bundle in the hold matches that certificate when measured on site.

How 300×300 ERW Hollow Sections Fit Structural Frame Geometry

A 300×300 square hollow section in Q345 sits at the intersection where column load capacity meets connection simplicity — the flat faces allow direct bolted or welded node plates without complex gusset profiling. On EPC industrial projects across the Middle East and Southeast Asia, we supply these sections pre-cut to erection length, with connection holes punched per approved shop drawings, so the steel arrives ready to bolt rather than requiring field modification. The ERW process produces a consistent weld seam along the longitudinal joint, and when paired with our in-house shot blasting and painting line, the surface preparation meets Sa 2.5 before the first coat goes on — eliminating the coordination gap between material supplier and coating subcontractor that so often causes adhesion failures.

Structural Compliance and Certification Pathways for Global Projects

Engineering specifications for steel frames typically call for compliance with EN 1993-1-1 for Eurocode projects or AISC 360 for North American designs, and the hollow section itself must conform to a recognized product standard such as EN 10210 for hot-finished or EN 10219 for cold-formed welded sections. [NEED_CITE: steel grade equivalence mapping between GB Q-series and EN S-series] For European customs clearance, CE marking under EN 10210 or EN 10219 is mandatory, and the declaration of performance must reference the specific factory production control system — a document our ISO 9001-certified quality management generates automatically for each heat. In corrosion-prone environments such as coastal logistics centers or chemical plant galleries, the choice between hot-rolled oiled surface and post-fabrication galvanizing directly affects both the initial procurement cost and the twenty-year maintenance cycle, and our engineering team reviews this with the specifier before the purchase order is finalized.

Reading the Steel Grade Designation: Q235, Q345, S235JR, S355JR

The Q-series grades follow the Chinese GB/T 1591 system where the number after “Q” indicates the minimum yield strength in MPa — so Q235 delivers approximately 235 MPa yield, while Q345 steps up to roughly 345 MPa, allowing smaller section sizes for the same design load. The European S-series works identically: S235JR and S355JR correspond closely to Q235 and Q345 respectively, with the “JR” suffix denoting room-temperature Charpy impact toughness of 27J. [NEED_CITE: GB/T 1591 and EN 10025 grade equivalence tables] SS400, the Japanese JIS designation, sits in the same general strength band as Q235 and is frequently specified on projects in Southeast Asia where Japanese engineering consultants dominate. The ERW welding technique fuses the strip edges through electric resistance heating without filler metal, producing a weld zone that matches the parent material’s mechanical properties when the process parameters are correctly controlled — which is why certified welding procedure specifications and qualified welders matter more than the welding method itself. Wall thickness from 1 mm to 3 mm with ±1% tolerance means that on a 3 mm nominal wall, the minimum acceptable measurement is 2.97 mm — tight enough to prevent the negative-tolerance abuse that causes site rejections, yet realistic for ERW production capability.

The Hidden Price of Accepting Non-Compliant Hollow Sections

When a fabricator delivers Q345 sections that actually carry Q235 chemistry, or when wall thickness falls below the declared tolerance, the consequences cascade far beyond the material invoice. Structural engineers cannot sign the erection completion certificate, the building occupancy permit gets delayed, and if the discrepancy surfaces after handover, the liability exposure includes potential demolition and reconstruction of load-bearing frames. [NEED_CITE: consequences of material non-compliance in structural steel construction] Certification gaps create customs holds — a shipment without a valid CE declaration of performance or without traceable mill test certificates linked to heat numbers will sit in the destination port accumulating demurrage charges while the paperwork gets sorted. The cost of sourcing from a vertically integrated producer who controls both the steelmaking and the fabrication is not measured in per-tonne price alone, but in the elimination of these downstream risks.

Why Project Buyers Source This Q235 Q345 Welded Square and Rectangular Steel Tube From Us

Our facility operates three dedicated ERW production lines backed by our own steel mill, meaning the slab that becomes your 300×300 Q345 column never passes through a third-party trader’s inventory — the heat number on the tube matches the chemistry in our laboratory records, and we can produce that chemistry to order rather than pulling from whatever grade happens to be in stock. We hold over 2,800 specification combinations in our rolling schedule, so when your shop drawing calls for a non-standard rectangular size or a cut length that differs from the usual 6 m or 12 m, we adjust the mill setup rather than asking you to accept a substitute. Every Q235 Q345 welded square and rectangular steel tube leaving Jinan carries a mill test certificate showing chemical composition and mechanical properties specific to that heat, and we welcome SGS, BV, or TÜV inspection at any production stage — our quality department prepares the WPS, PQR, weld maps, and dimensional inspection reports as a standard documentation package, not as a special request. Our welding procedures are certified to AWS and EN standards, our welders hold current qualifications, and our shot blasting and painting line handles surface preparation and coating in the same facility where the tubes are formed — one quality system, one point of accountability from raw material to finished component.

Documentation & Compliance

• Mill test certificate documenting Q235 or Q345 chemical composition and mechanical properties per GB/T 1591, with heat number traceability to the original slab
• CE certificate of conformity for EN 10219 cold-formed welded hollow sections, required for European Union customs clearance and site acceptance
• ISO 9001 quality management system certificate covering the full production chain from steelmaking through ERW forming, cutting, and surface treatment
• SGS or BV third-party inspection report available at any hold point — dimensional verification, visual weld inspection, and coating thickness measurement
• Material traceability register linking each bundle’s heat number to the corresponding mill test certificate and production date
• Export documentation package including commercial invoice, packing list, bill of lading, and certificate of origin formatted for the destination country’s customs requirements

Packaging, Loading & Delivery

• Hot-rolled Q235 and Q345 square and rectangular tubes bundled with galvanized steel straps at intervals matching the 6 m, 6.4 m, or 12 m length, with end caps protecting the oiled surface from transit abrasion
• Seaworthy packaging using waterproof wrapping and wooden cradle supports for 300×300 sections, preventing ovalization during ocean freight and crane handling at the destination port
• Container loading optimized for 12 m lengths in 40-foot open-top or flat-rack units, with weight distribution calculated to stay within road transport limits at the delivery site
• Custom cut-to-length service available before packing — sections cut to erection sequence length and labeled with piece marks matching the approved shop drawings
• Heat number and steel grade stenciled on each bundle tag, with color-coding by grade to prevent mixing on site during erection
• Delivery terms FOB, CIF, or DDP to project site, with complete export documentation and real-time shipment tracking until arrival

Starting Your Procurement for Q235 Q345 Welded Square and Rectangular Steel Tube

Send your project drawings in PDF or DWG format along with the specified steel grade, section sizes, wall thickness, quantities, and destination port — our engineering team responds within one day with a preliminary assessment, detailed quotation covering material, fabrication, coating, packing, and freight, plus a shop drawing timeline and production schedule. If your project requires non-standard dimensions, third-party inspection coordination, or CE certification documentation for European delivery, confirm these requirements in the initial inquiry so we can include them in the proposal without revision cycles.

Request Your Quotation and Mill Test Certificate

Submit your specifications, steel grade, and quantity to receive a detailed offer with full material documentation.

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Frequently Asked Questions

Q: How do Q235 and Q345 grades compare to S235JR and S355JR for European projects?

A: Q235 and S235JR both provide approximately 235 MPa minimum yield strength, while Q345 and S355JR deliver approximately 345 MPa. The chemical compositions are closely aligned, and for most structural applications they are interchangeable — however, European-specification projects require the mill test certificate to reference EN 10025 or EN 10219, and our documentation package can be prepared to either standard upon request.

Q: Can you provide third-party inspection before shipment for Middle East and African projects?

A: Yes. We coordinate SGS, BV, or TÜV inspection at any production hold point — including dimensional verification, visual and NDT weld inspection, surface treatment measurement, and final packing review. The inspection report becomes part of the export documentation package submitted with the shipment.

Q: What is the minimum order quantity for custom-cut lengths and non-standard sizes?

A: The standard MOQ is 5 tons. For custom cut-to-length or non-standard rectangular dimensions outside our regular rolling schedule, we review the requirement against our mill setup capabilities and confirm feasibility and any additional lead time in the quotation.

Q: How does theoretical weight invoicing work with the ±1% wall thickness tolerance?

A: We invoice by theoretical weight calculated from the nominal dimensions and standard density, which provides cost predictability for your budget. The ±1% tolerance ensures that actual wall thickness remains within a narrow band around the nominal value — on a 3 mm wall, the minimum is 2.97 mm — preventing the excessive negative tolerance that leads to site rejections and structural concerns.

Q: Do you supply CE-marked hollow sections for European Union construction projects?

A: Yes. Our Q235 Q345 welded square and rectangular steel tube production is CE-certified under EN 10219 for cold-formed welded hollow sections. The CE declaration of performance, factory production control certificate, and heat-specific mill test certificates are included in the standard documentation package for EU delivery.