Description
Factory-Direct ERW Square Tubes — Three dedicated production lines running Q235 and S235 welded square tubes from 10×10 to 600×600 mm with ±1% wall tolerance, shipped with original mill test certificates.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Welded Square Tube |
| Product Type | Welded Square Steel Tube (ERW) |
| Steel Grade | Q195, Q215, Q235, Q345, GR.A, GR.B, S235, S355 |
| Standard | ASTM, EN, ISO 9001 |
| Section Shape | Square |
| Size Range | 10×10 – 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 / Furniture |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, scaffolding systems, column supports, roof trusses |
| Machinery & Equipment | Equipment base frames, conveyor structures, machine guards |
| Industrial Projects | Pipeline support racks, warehouse frameworks, platform structures |
| Furniture & Interior | Display racks, shelving systems, structural brackets |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A ±1% tolerance on a 3 mm wall means the difference between passing SGS inspection and losing an entire container’s profit to return freight.
Early in my career, a batch of RHS tubes shipped to Europe had wall thickness pushed to the negative tolerance edge. The client’s SGS re-inspection flagged non-conformance, and the whole container came back — the return freight alone wiped out the margin on that shipment. Since then, I check wall tolerance before I check price. Every batch of EN Standard Carbon Steel Welded Square Tube leaving our facility goes through three rounds of in-house lab measurement before it ever reaches the loading bay. When you are sourcing welded square tubes for structural frames or scaffolding, inconsistent wall thickness does not just mean a paperwork headache at customs — it means load-bearing calculations built on assumed dimensions that do not match what arrives on site [NEED_CITE: EN 10219 cold-formed welded structural hollow sections dimensional tolerances].
How ERW Welded Square Tubes Match Structural Frame Requirements
Structural frames demand predictable load transfer at connection points, and the square cross-section of these ERW welded tubes provides flat bearing surfaces on all four sides — critical when bolting to gusset plates or welding into moment frames. The Q235 and S235 grades cover the yield range that most general construction and scaffolding applications require, while Q345 and S355 step up for heavier industrial platforms. Our 3 production lines hold 2,800+ specifications in ready stock, which means a project procurement team ordering mixed sizes for a warehouse framework does not need to wait for separate mill runs on each dimension.
Engineering Compliance and Certification Pathways
For projects in the European market, the EN Standard Carbon Steel Welded Square Tube must conform to EN 10219 dimensional and mechanical requirements, and the CE marking under EN 10210/EN 10219 is non-negotiable for structural applications — without it, customs clearance stalls and the engineer of record cannot sign off [NEED_CITE: CE marking requirements for structural steel hollow sections in EU member states]. In North American projects, ASTM A500 Grade B or Grade C equivalents apply. The surface treatment choice — bare for indoor use, pre-galvanized for moderate corrosion environments, hot-dipped galvanized for outdoor or coastal exposure — directly affects the maintenance cycle and service life of the installed structure. Plain ends arrive ready for on-site cutting, drilling, and welding without additional edge preparation.
Steel Grade Selection and ERW Welding Fundamentals
The Q-series grades (Q195, Q215, Q235, Q345) follow the Chinese GB/T standard system where the number indicates minimum yield strength in MPa, while S235 and S355 follow the European EN system with the same naming logic. GR.A and GR.B map to ASTM A500 specifications for North American projects. Understanding grade equivalence across these systems prevents ordering errors — a common source of delays when material arrives but the engineer rejects it because the certificate references an unfamiliar designation [NEED_CITE: steel grade equivalence between EN, ASTM, and GB standards for structural hollow sections]. The ERW welding process forms the square profile from coiled strip through continuous forming and high-frequency electric resistance welding, producing a longitudinal weld seam. This process suits the 10×10 to 600×600 mm range efficiently, offering lower cost than seamless alternatives while maintaining consistent wall thickness across the cross-section. Invoicing by theoretical weight means your cost calculation is based on standard density and nominal dimensions — the ±1% tolerance ensures actual weight stays close to the theoretical figure, avoiding disputes over weight-based pricing.
Hidden Costs of Procuring Without Verified Tolerance Data
Ordering welded square tubes based on price alone, without confirmed mill test certificates and independent tolerance verification, exposes the project to three categories of hidden cost. First, wall thickness below the declared tolerance reduces actual load-bearing capacity — the structural engineer’s calculations assume nominal dimensions, and under-thickness material fails inspection. Second, missing or incomplete CE certification triggers customs holds at the destination port, generating demurrage charges and delaying the construction schedule. Third, material without heat-number traceability cannot be verified against the mill test certificate, which means the entire batch may be rejected during third-party inspection — the cost of replacement material plus expedited freight falls entirely on the buyer [NEED_CITE: consequences of non-conforming structural steel in construction project compliance].
Procurement Confidence Through Verified Supply Chain Control
Our factory-direct model eliminates intermediary markups — the price you receive comes straight from the production floor in Jinan, with volume discount programs available for recurring procurement partners. Every EN Standard Carbon Steel Welded Square Tube batch ships with original mill test certificates documenting chemical composition and mechanical properties, and our in-house理化实验室 conducts three-stage inspection before any material clears for loading. For buyers requiring independent verification, SGS or BV third-party inspection is available on request. The 2,800+ ready-stock specifications mean that mixed-size container orders — common in construction projects requiring multiple square tube dimensions — can be consolidated and loaded professionally, optimizing container space and reducing per-unit freight cost. Custom non-standard dimensions and cut-to-length orders are supported with flexible MOQ starting from 1 ton.
Documentation & Compliance
- Mill test certificate documenting Q235 and S235 chemical composition and mechanical properties per EN 10219, with heat number traceability
- CE certificate covering EN 10210 and EN 10219 structural hollow section compliance for European market customs clearance
- ISO 9001:2015 quality management system certificate covering production and inspection processes
- SGS or BV third-party inspection report available upon request for independent quality verification
- Material traceability documentation linking each bundle to its heat number and production batch
- Complete customs document package including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Bare and oiled Q235 square tubes bundled with steel strips in seaworthy packaging, with edge protectors on pre-galvanized and hot-dipped galvanized bundles to preserve the zinc coating during ocean transit
- 5.7 m and 6 m standard lengths loaded into 20ft and 40ft containers with professional stacking plans that maximize weight utilization while preventing deformation of thinner-wall tubes (0.8–2.0 mm range)
- Mixed-size orders consolidated into single containers with dimensional optimization — a typical project order combining 50×50, 100×100, and 200×200 mm square tubes loaded to full container weight capacity
- Heat number and steel grade markings stenciled on each bundle for on-site identification and traceability verification
- FOB, CIF, and DDP shipping terms available with real-time tracking and professional export documentation handling
- Cut-to-length service available for orders requiring non-standard lengths within the 5.7 m / 6 m range
Start Your Bulk Procurement With Verified Documentation
Submit your specification sheet — including square tube dimensions, wall thickness, steel grade, surface treatment preference, quantity, and destination port — and receive a factory-direct quotation with volume pricing within 12 hours. For non-standard dimensions or mixed-size project orders, request a consolidated loading plan and delivery schedule. Confirm certification requirements (CE/EN for Europe, ASTM for North America) and third-party inspection needs before production begins.
Get Factory-Direct Pricing With Mill Test Certificates
Send your specifications to admin@sdxinjiyuan.com or reach us via WhatsApp at +86 188 5315 7756 for a quotation and sample arrangement.
Frequently Asked Questions
Q: What is the grade equivalence between Q235, S235, and ASTM A500 Grade B?
A: Q235 (GB/T standard), S235 (EN standard), and ASTM A500 Grade B share similar yield strength ranges and are commonly used interchangeably in general structural applications. We provide mill test certificates referencing the standard specified in your purchase order, and our team can advise on grade substitution if your project requires cross-standard compliance.
Q: How do you verify wall thickness tolerance on EN Standard Carbon Steel Welded Square Tube?
A: Every batch undergoes three-stage in-house inspection using calibrated ultrasonic thickness gauges and calipers at multiple points along the tube length. Original mill test certificates accompany each shipment, and SGS or BV third-party inspection is available for buyers who require independent verification before loading.
Q: Can you produce non-standard square tube dimensions with small order quantities?
A: Yes. Beyond the 10×10 to 600×600 mm standard range, we support custom dimensions and cut-to-length orders. The MOQ starts from 1 ton, making trial orders feasible for project evaluation before committing to full-container volumes.
Q: Which surface treatment should I choose for outdoor structural applications?
A: For outdoor or corrosive environments, hot-dipped galvanized provides the longest service life with a thick zinc coating. Pre-galvanized suits moderate exposure conditions at lower cost. Bare tubes with oil coating work for indoor applications or projects where on-site painting will be applied. We supply all three options from the same production lines.
Q: How does theoretical weight invoicing affect my total cost?
A: Invoicing by theoretical weight means your cost is calculated using standard steel density and nominal dimensions rather than actual weighed mass. With our ±1% wall thickness tolerance, the actual weight stays close to theoretical, ensuring pricing transparency and preventing disputes over weight-based billing.
Request Your Quotation With Full Certification Package
Email your project specifications to admin@sdxinjiyuan.com or contact us at +86 188 5315 7756 (WhatsApp) to receive factory-direct pricing, mill test certificate samples, and delivery confirmation for your EN Standard Carbon Steel Welded Square Tube order.
