Description
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B ERW Welded Square Steel Tube |
| Product Type | Welded Square Steel Tube (ERW) |
| Steel Grade | Q195, Q235, Q235B, Q345, Q345B, S235JR, S275JR, S355JR, St37, St37-2, St42, St35, St35.4, St52.4 |
| Standard | ASTM, EN 10219, EN 10210 |
| Section Shape | Square / Rectangular |
| Size Range | 40×40 mm, 40×60 mm, 40×80 mm and broader sizes |
| Wall Thickness | Per standard tolerance ±1% |
| Length | 6 m / 6.4 m / 12 m |
| Technique | ERW (Electric Resistance Welded) |
| Surface Treatment | Hot Rolled, Non-oiled (Black Finish) |
| Ends | Plain Ends, Custom Cutting Available |
| Application | Structure Pipe, Fluid Pipe, Gas Pipe, Boiler Pipe, Hydraulic Pipe, Chemical Fertilizer Pipe, Drill Pipe |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, scaffolding systems, column supports, roof trusses |
| Machinery & Equipment | Conveyor structures, machine base frames, hydraulic cylinder housings |
| Oil & Gas | Low-pressure fluid conveyance, gas distribution lines, drilling support structures |
| Industrial Fabrication | Storage rack systems, workshop mezzanines, equipment enclosures |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A ±1% tolerance deviation on a 40×80 carbon steel square tube 40×60 40×80 ERW welded supplier batch can trigger full-lot rejection at the project site.
I have seen containers held at port because the wall thickness fell outside the acceptable negative tolerance range. The site engineer pulled a caliper, measured three random pieces, and flagged the entire shipment. Twenty-plus tons of black-finish ERW tubes sat in a warehouse warehouse accumulating surface oxidation while the procurement team scrambled for replacement material. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements] When the steel grade documentation does not match the physical product, customs officers in strict-import markets can hold the cargo for weeks. Fragmented sourcing from multiple suppliers compounds this risk — different mills, different tolerance practices, different certificate formats. The cost is never just the steel price; it is the idle crane, the delayed weld crew, the re-submitted inspection paperwork.
How ERW Black-Finish Square Tubes Match Structural Fabrication Requirements
The hot-rolled black finish on this carbon steel square tube 40×80 40×60 ERW welded supplier product provides a clean, non-oiled surface that accepts paint, powder coating, or galvanizing without additional degreasing. For structural frames and machinery bases, the ERW weld seam runs straight and uniform along the length, providing consistent load distribution at connection points. The 6 m and 12 m standard lengths reduce on-site welding joints, while custom cutting to project-specific dimensions eliminates field waste. Our production lines run three shifts simultaneously, and we maintain ready stock of 40×60 and 40×80 sizes so that urgent project modifications do not wait for a new heat to be rolled.
Engineering Compliance and Certification Pathways
Structural projects governed by EN 1993 (Eurocode 3) require verifiable material traceability back to the original heat number. [NEED_CITE: EN 10219 structural hollow section certification and CE marking requirements] For European market entry, the carbon steel square tube 40×80 40×60 ERW welded supplier must carry CE certification under EN 10219 or EN 10210, with Factory Production Control (FPC) documentation. North American projects referencing ASTM A500 require mill test certificates showing chemical composition and mechanical properties per heat. Our in-house lab conducts three-stage inspection — incoming raw material, in-process weld seam verification, and final dimensional check — with every batch backed by original mill test certificates. Third-party inspection through SGS or BV is available before container sealing, providing independent verification for projects with strict compliance requirements.
Steel Grade Selection and ERW Process Fundamentals
The Q-series grades (Q195 through Q345B) follow the Chinese GB standard system, where the number indicates minimum yield strength in MPa. Q235B is the most widely specified grade for general structural work, offering a balance of formability and weldability. The S-series (S235JR, S275JR, S355JR) follows the European EN standard system, with equivalent mechanical property ranges. [NEED_CITE: steel grade equivalence between GB Q-series and EN S-series standards] The ERW (Electric Resistance Welded) process forms the tube by rolling hot-rolled steel coil into a square or rectangular cross-section and welding the seam through electrical resistance heating — no filler metal is added. This produces a uniform weld seam with mechanical properties approaching the parent material. The hot-rolled black finish means the tube is delivered non-oiled, directly from the mill, with a natural iron oxide surface layer that provides short-term corrosion protection during storage and transit.
Hidden Costs of Incorrect Grade Specification and Missing Documentation
Ordering S235JR when the structural engineer specified S355JR means the tubes will fail load-bearing verification on site — the yield strength gap is not negotiable. [NEED_CITE: structural steel grade substitution risks in load-bearing applications] Similarly, shipping to a European port without CE certification under EN 10219 means customs will not release the cargo, regardless of the physical product quality. Negative tolerance abuse — where the actual wall thickness falls below the specified minimum — reduces the load-carrying capacity and violates the engineering design assumptions. The re-cost includes return freight, replacement production, project delay penalties, and in severe cases, structural safety reviews. Every batch of our carbon steel square tube 40×80 40×60 ERW welded supplier product is invoiced by theoretical weight with full dimensional compliance, eliminating the ambiguity between ordered and delivered specifications.
Direct Factory Supply with Full Traceability and Export Capability
As a factory-direct supplier operating three production lines with monthly capacity exceeding 20,000 tons, we eliminate the markup and communication delays of intermediary traders. Our inventory covers 2,800+ specifications across square tubes, rectangular tubes, round pipes, steel plates, and section steel — meaning a single purchase order can consolidate multiple product categories into one container, reducing freight cost per ton. Every heat is tested in our in-house理化实验室, and original mill test certificates are issued with chemical composition, yield strength, tensile strength, and elongation data. We hold ISO 9001:2015, Lloyd’s CE (EN 10210/EN 10219), and FPC certifications, and we arrange SGS or BV third-party inspection on request. Our export team handles documentation, customs clearance, and container loading optimization — including professional weight distribution plans for heavy steel cargo — serving buyers in 50+ countries with recurring procurement programs and volume-based pricing reviews every six months.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition and mechanical properties per EN 10219, issued per heat number
- CE certificate covering EN 10219 and EN 10210 cold-formed welded structural hollow sections, with FPC factory production control records
- ISO 9001:2015 quality management system certificate covering the full production process from raw material to finished tube
- SGS or BV third-party inspection report available upon request, verifying dimensional tolerance, surface quality, and weld seam integrity
- Full material traceability from coil heat number through ERW welding, cutting, and final bundling
- Complete customs document package: commercial invoice, packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Black-finish ERW square tubes bundled with steel straps and edge protectors to prevent surface scratching and maintain the non-oiled finish during ocean transit
- 6 m and 12 m lengths loaded in dedicated containers with wooden chocks and anti-shift bracing, optimized for 40×60 and 40×80 cross-sections to maximize payload per container
- Custom cutting to project-specific lengths available, with each piece marked by heat number, steel grade, and size for on-site identification
- Container loading plans prepared by our export team, balancing weight distribution across axles and ensuring compliance with port handling equipment limits
- FOB, CIF, and DDP shipping terms available, with door-to-door logistics coordination for project sites requiring direct delivery
Getting a Project-Specific Quote for Your Structural Steel Requirements
Submit your specification sheet — including size, wall thickness, steel grade, total quantity, and destination port — and receive a detailed quotation within 12 hours, complete with mill test certificate samples and container loading estimates. For non-standard sizes or custom cutting requirements, our technical team will confirm feasibility and lead time based on current production scheduling.
Request Your Quotation and Mill Test Certificate
Send your requirements to admin@sdxinjiyuan.com or contact us via WhatsApp at +86 188 5315 7756. Our team will respond with pricing, certification documentation, and delivery scheduling for your carbon steel square tube 40×80 40×60 ERW welded supplier order.
