Description
Factory-Direct Pricing, No Middlemen — Every Q235B welded square and rectangular steel tube rolls off our ERW lines in Jinan, shipped with original mill test certificates and CE documentation straight to your port.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B Welded Square and Rectangular Steel Tube |
| Product Type | Welded Square and Rectangular Steel Tube (RHS/SHS) |
| Steel Grade | Q235B, Gr.B, S235, S275, S355, STK400 |
| Standard | ASTM A500, ASTM A53, GB/T 3091 |
| Section Shape | Square and Rectangular |
| Size Range | 15mm×20mm – 700mm×800mm |
| Wall Thickness | 1 – 30 mm |
| Length | 5.8m / 6m / 11.8m / 12m / Random Length |
| Technique | ERW (Welded) |
| Surface Treatment | Black Painting / Galvanized / Varnish / Bare |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures / Construction frames / Curtain walls / Support tubes / Building structures |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors | Industrial plant steel frames, pipe rack supports, equipment platform structures |
| Construction Companies | High-rise building columns, curtain wall mullions, scaffolding uprights |
| Machinery Manufacturers | Conveyor frames, equipment base plates, hydraulic support columns |
| Infrastructure Developers | Bridge handrail posts, sound barrier supports, solar mounting structures |
What Negative Tolerance Actually Costs on a Q235B Structural Frame Order
A wall thickness that reads 2.7mm instead of 3.0mm on paper can fail third-party inspection at destination port.
I have seen entire container loads of RHS rejected because the negative tolerance drifted beyond acceptable limits. The buyer paid for 3mm Q235B welded square and rectangular steel tube, received 2.6mm average, and the SGS inspector at the Middle East port flagged every single piece. Reload costs, air-freight replacements, and a three-week project delay — all because the mill skipped the ultrasonic wall-thickness check on the ERW weld seam. When your structural engineer signs off on ASTM A500 calculations, the delivered product must match the specified grade and thickness to the decimal. [NEED_CITE: EN 10219 cold-formed welded hollow section dimensional tolerance requirements]
How Q235B RHS/SHS Matches Structural Frame Requirements
Q235B welded square and rectangular steel tube in the 100×100mm to 300×300mm range with 4–12mm wall thickness handles typical building frame loads where S235JR or S355JR would be over-specified for non-critical members. The ERW process produces a consistent weld seam that passes ultrasonic inspection, and our in-house lab checks every heat number for chemical composition before the tube leaves the line. For curtain wall mullions and secondary support tubes, the ±1% tolerance keeps connection plates flush without on-site grinding — a detail that matters when your installation crew is working at height with a crane on standby.
Engineering Compliance and Certification Pathways
Structural frames destined for EU markets require CE marking under EN 10210 (hot-formed) or EN 10219 (cold-formed welded), and customs authorities in Germany, Netherlands, and Singapore will hold shipments without valid Factory Production Control certificates. Q235B welded square and rectangular steel tube supplied under GB/T 3091 meets Chinese domestic codes, but projects specifying ASTM A500 Gr.B or EN 10219 S235JR need mill test certificates that explicitly reference those standards. [NEED_CITE: steel grade equivalence mapping between GB Q235B and EN S235JR / ASTM A500 Gr.B] Surface treatment selection — black painting for indoor frames, hot-dip galvanized for outdoor or coastal environments — must align with the project’s corrosion category classification, and the coating thickness needs independent measurement before container sealing.
Steel Grade Selection and ERW Process Fundamentals
Q235B sits at the entry level of Chinese carbon structural steel, offering adequate formability and weldability for general construction frames where ultimate strength is not the governing design factor. When projects step up to S275 or S355, the yield strength increase allows thinner wall sections for the same load capacity, reducing overall weight and material cost — but the ERW weld quality becomes more critical because higher-strength grades are less forgiving of weld seam defects. Our ERW lines produce Q235B welded square and rectangular steel tube with inline eddy-current testing on the weld seam, and the physical lab verifies that each heat meets the specified grade’s chemical boundaries before the tube enters the sizing mill. For sharp-corner rectangular tubes — a proprietary process we developed across multiple patents — the corner radius approaches zero, giving flush contact with connection plates and eliminating the gap-filling shims that round-corner RHS requires in precision machinery frames.
Hidden Costs of Unverified Material and Missing Documentation
Ordering Q235B welded square and rectangular steel tube from a trading company without direct mill access means you receive whatever certificate they photocopy — not what the lab actually tested. When the destination port authority requests a 3.2 inspection certificate under EN 10204 and the supplier cannot produce one tied to the specific heat number, the container sits at the terminal accumulating demurrage charges. [NEED_CITE: EN 10204 inspection certificate types and their role in steel import customs clearance] Beyond customs, structural engineers who discover material substitution after erection face the choice of costly reinforcement or full member replacement — a scenario that traces back to accepting the lowest unit price without verifying the mill test certificate against the purchase order specifications.
Why Procurement Teams Source Q235B RHS/SHS Directly from Our Jinan Facility
We operate three dedicated ERW production lines covering over 2,800 specifications in square, rectangular, and round profiles, with wall thickness reaching 40mm on custom orders. Every Q235B welded square and rectangular steel tube passes through our on-site physical and chemical laboratory — not a third-party lab we send samples to, but our own equipment, our own technicians, generating the mill test certificate that ships with your container. Our proprietary sharp-corner rectangular tube technology holds 41 invention patents and fills a specification gap that standard catalogues from most mills cannot address. We hold CE certification under EN 10210 and EN 10219, ISO 9001:2015 registration, and Singapore FPC approval, with SGS and BV available for third-party inspection at your request. For projects spanning multiple steel categories — tubes, plates, beams, fabrication — we consolidate production and loading into a single shipment, eliminating the coordination overhead of managing five different suppliers.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition (C, Si, Mn, P, S) and mechanical properties per GB/T 3091, with heat number traceability
- CE certificate under EN 10219 for cold-formed welded structural hollow sections, required for EU market customs clearance
- ISO 9001:2015 quality management system certificate covering the full production and inspection process
- SGS or BV third-party inspection report available upon request, verifying dimensional tolerance, surface treatment thickness, and weld seam quality
- Material traceability sheet linking each bundle to its heat number, production date, and laboratory test results
- Full customs document package including packing list, bill of lading, certificate of origin, and commercial invoice
Packaging, Loading & Delivery
- Q235B welded square and rectangular steel tube bundled with steel strips at intervals matching the 6m or 12m length, with edge protectors on galvanized surfaces to prevent zinc coating damage during transit
- Black-painted or bare tubes receive anti-rust oil coating on inner and outer surfaces before bundling, preventing corrosion during ocean freight to Southeast Asia or Middle East ports
- Container loading plans optimized for 15×20mm small-section tubes (high piece count per 20ft container) versus 700×800mm large-section RHS (requires 40ft open-top or flat-rack configuration)
- Random length or cut-to-order lengths available within the 5.8m–12m range, with kerf allowance calculated for your fabrication drawings
- Each bundle tagged with heat number, steel grade Q235B, section dimensions, wall thickness, and production batch for site identification
- FOB Jinan/Qingdao, CIF destination port, or DDP door-to-door delivery with real-time container tracking
How to Initiate Your Q235B RHS/SHS Procurement
Submit your specification sheet — section dimensions, wall thickness, total tonnage, steel grade, surface treatment preference, and destination port — and receive a detailed quotation within 12 hours, including unit pricing, production lead time, payment terms, and the applicable mill test certificate format. For non-standard dimensions outside the 15×20mm to 700×800mm catalogue range, our engineering team reviews feasibility and provides a custom production proposal with confirmed tooling lead time.
Request Your Q235B Welded Square and Rectangular Steel Tube Quotation
Send specifications via email or WhatsApp to receive pricing, mill test certificate samples, and container loading plans within one business day.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjysteel.com
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjysteel.com
Frequently Asked Questions
Q: What is the difference between Q235B, S235JR, and ASTM A500 Gr.B for welded square and rectangular steel tubes?
A: Q235B is the Chinese standard carbon structural steel grade under GB/T 700, S235JR is the European equivalent under EN 10025, and ASTM A500 Gr.B is the North American specification for cold-formed welded structural tubing. All three share similar yield strength ranges and chemical composition boundaries, but the mill test certificate must explicitly reference the standard your project specification requires. We supply Q235B welded square and rectangular steel tube and can issue certificates conforming to any of these three standards based on your engineer’s designation.
Q: How do you verify wall thickness tolerance on ERW welded tubes before shipment?
A: Every Q235B welded square and rectangular steel tube undergoes ultrasonic wall-thickness measurement at multiple points along the length, with particular attention to the ERW weld seam zone where thinning can occur during the forming process. Our in-house laboratory records measurements against the ordered nominal thickness, and the mill test certificate includes dimensional inspection results. Third-party SGS or BV inspection is available if your project requires independent verification before container loading.
Q: Can you produce non-standard dimensions outside the 15×20mm to 700×800mm range?
A: Yes. Beyond our standard catalogue of over 2,800 specifications, we manufacture custom non-standard square and rectangular tubes to your drawing dimensions, including special wall thickness ratios and proprietary sharp-corner profiles where the corner radius approaches zero for flush connection plate contact. Custom orders require confirmation of tooling availability and production lead time, which we provide within 24 hours of receiving your specification.
Q: What surface treatment options are available and how do they affect pricing?
A: Q235B welded square and rectangular steel tube is available in black painting (standard anti-rust coating for indoor applications), hot-dip galvanized (zinc coating for outdoor or corrosive environments), varnish coating, or bare (uncoated, with mill oil for temporary protection). Hot-dip galvanizing adds processing cost and extends production time by several days, but provides corrosion resistance measured in decades rather than months for structures exposed to weather or coastal atmospheres.
Q: What documentation do you provide for EU customs clearance?
A: For European Union imports, we supply CE certification under EN 10219 (cold-formed welded structural hollow sections) along with the Factory Production Control certificate, mill test certificates per EN 10204 Type 3.1, packing list, bill of lading, certificate of origin, and commercial invoice. The CE mark and FPC certificate are mandatory for customs clearance in EU member states, and we ensure all documentation cross-references the heat numbers and production batch shipped in your container.
