Description
Factory-direct pricing, zero middlemen markup — every Q235 Q345 welded square steel tube rolls off our own ERW lines in Jinan, shipped with full mill documentation straight to your port.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345 Welded Square Steel Tube |
| Product Type | Welded Square / Rectangular Steel Tube |
| Steel Grade | Q195, Q215, Q235, Q345, GR.A, GR.B, S235, S355 |
| Standard | ASTM A213, DIN EN 10217-1 |
| Section Shape | Square / Rectangular |
| Size Range | 20 mm – 80 mm+ (customizable) |
| Wall Thickness | 0.8 – 30 mm |
| Length | 0.1 m – 11.8 m (100 mm – 11,800 mm) |
| Technique | Welded (ERW) |
| Surface Treatment | Pre-galvanized / Hot-dipped galvanized / Bare / Oiled / Black |
| Tolerance | ±1% |
| Ends | Plain / Beveled (per order) |
| Application | Steel structures, fences, posts, warehouse and building construction |
| MOQ | 10 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors & Construction | Warehouse frames, building columns, scaffolding uprights, steel posts |
| Machinery Manufacturers | Equipment base frames, conveyor support structures, automation rigging |
| Infrastructure & Fencing | Highway guardrail posts, perimeter fencing, municipal light pole foundations |
What Negative Tolerance Really Costs on a 28-Ton Container
A few percent of wall thinning turns into tons of missing weight before the container even reaches the port.
I once watched a Dubai client reject an entire 28-ton shipment of 40×40 black square tubes on site — negative tolerance had crept past 8%, and the actual weight came up nearly two tons short. The calipers came out, the paperwork was scrutinized, and the cargo sat at Jebel Ali for weeks. Since then, I personally stand in the lab while every batch gets measured before it leaves the factory, locking tolerance within ±1%. For buyers sourcing a Q235 Q345 welded square steel tube, that discipline is the difference between a clean customs release and a demurrage bill [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements].
Matching Wall Thickness and Grade to Structural Load Paths
When a warehouse frame calls for Q345 at 3 mm wall, swapping to Q235 at the same thickness drops the load-bearing margin significantly — the yield point gap between the two grades is not something you recover with extra bracing. Our ERW lines run the full Q195–Q345 range alongside S235/S355 for European-spec projects, so engineers get the exact grade the structural calculation demands. A Q235 Q345 welded square steel tube in 0.8 mm wall serves light-duty fencing; the same profile at 30 mm wall carries heavy industrial frames — the specification range covers both without splitting the order across suppliers.
Engineering Compliance and Certification Pathways
EU projects require CE marking under EN 10210 or EN 10219; without it, customs holds the cargo regardless of how good the steel is [NEED_CITE: CE marking requirements for structural hollow sections under EN 10219]. North American buyers typically reference ASTM A500 or ASTM A213, and the mill test certificate must trace back to heat numbers for every bundle. Our in-house physical and chemical lab runs composition and mechanical checks on every heat, and third-party inspection by SGS or BV is arranged before loading — not after a problem surfaces at destination.
ERW Welding, Surface Treatment, and the Sharp-Corner Advantage
ERW welded tube offers lower cost and tighter dimensional control than seamless for structural applications below high-pressure service. Surface treatment selection depends on the environment: pre-galvanized for indoor or mild exposure, hot-dipped galvanized for outdoor or coastal sites, bare or oiled for projects where field welding or painting follows. Our proprietary sharp-corner rectangular tube technology — covered by 41 invention patents — produces true 90° internal corners that fit flush against gusset plates and connection brackets, eliminating the gap-filling shims that round-corner tubes require on architectural and machinery frames.
The Hidden Price of Unverified Steel Grades
Ordering Q345 and receiving Q235 with a forged certificate does not show up until the structure fails inspection — or worse, during service. Missing CE documentation delays EU customs by weeks; absent heat-number traceability voids the engineer’s sign-off. A Q235 Q345 welded square steel tube sourced without proper mill test certificates may save a few dollars per ton at purchase, but the rework, delay, and liability costs dwarf that saving [NEED_CITE: consequences of non-compliant steel grade substitution in structural projects].
Why Procurement Teams Consolidate Square Tube Orders Here
We run three dedicated ERW production lines covering over 2,800 specifications — from 20 mm square at 0.8 mm wall to 80 mm+ at 30 mm wall — so a single purchase order covers fencing posts, warehouse columns, and machinery frames without splitting across vendors. Factory-direct pricing means no trading-company margin layered on. Every shipment carries a mill test certificate generated by our own lab, backed by CE EN 10210/EN 10219, ISO 9001:2015, and SGS/BV third-party verification. Non-standard sizes and custom lengths are produced to order, and our logistics team plans container loading to maximize weight per TEU — critical when shipping Q235 Q345 welded square steel tube to 50+ countries across the EU, North America, the Middle East, and Southeast Asia.
Documentation & Compliance
- Mill test certificate documenting Q235/Q345 chemical composition and mechanical properties per heat number, conforming to EN 10204 3.1
- CE certificate under EN 10210 / EN 10219 for structural hollow section compliance in EU markets
- ISO 9001:2015 quality management system certificate covering the full production and inspection process
- SGS or BV third-party inspection report available upon request before shipment
- Full customs document package: packing list, bill of lading, certificate of origin, and commercial invoice
Packaging, Loading & Delivery
- Black and oiled Q235/Q345 tubes bundled with steel strips and edge protectors; galvanized bundles wrapped to preserve the zinc coating during ocean transit
- Container loading plans optimized for 11.8 m lengths to maximize TEU weight utilization on 20ft and 40ft HC units
- Custom cut-to-length service available within the 0.1 m – 11.8 m range, with cut ends deburred and marked by heat number
- Heat number and steel grade stenciled on each bundle for site traceability and inspection readiness
- FOB, CIF, and DDP terms available with door-to-door logistics coordination to 50+ countries
Ready to Lock In Your Specification and Certification Package
Send your size range, steel grade, quantity, and destination port — we return a detailed quotation with unit price, delivery timeline, and applicable certification documents within 12 hours. Non-standard dimensions and sharp-corner rectangular tube requirements are quoted separately with production drawings confirmed before the deposit.
Get Your Quotation and Mill Test Certificate Today
Submit your Q235 Q345 welded square steel tube specifications via email at admin@sdxjysteel.com or WhatsApp at +86 188 5315 7756 to receive pricing, certification details, and container loading confirmation.
Frequently Asked Questions
Q: How do Q235 and Q345 (GB) map to S235/S355 (EN) and ASTM equivalents?
A: Q235 generally corresponds to S235 in the EN system and offers similar yield characteristics; Q345 aligns with S355 in yield class. ASTM equivalence depends on the specific grade and application — we provide cross-reference guidance with every quotation and confirm the correct designation on the mill test certificate.
Q: Can you provide SGS or BV third-party inspection and EN 10204 3.1 mill test certificates?
A: Yes. Every shipment includes an EN 10204 3.1 mill test certificate generated by our in-house lab. SGS and BV third-party inspections are arranged before loading at your request, with full reports included in the shipping document package.
Q: What is the MOQ for custom non-standard sizes or sharp-corner rectangular tubes?
A: The standard MOQ is 10 tons. Custom non-standard dimensions and sharp-corner rectangular tube profiles are produced to order — send your drawing or specification for a tailored quote with confirmed lead time.
Q: When should I choose pre-galvanized versus hot-dipped galvanized versus bare/oiled?
A: Pre-galvanized suits indoor or mild-exposure applications with uniform coating needs. Hot-dipped galvanized is specified for outdoor, coastal, or high-humidity environments requiring thicker zinc protection. Bare or oiled finish is selected when the tube will be field-welded, painted, or used in concealed structural applications.
Q: Do you offer FOB, CIF, and DDP shipping with professional container loading?
A: Yes. We handle FOB, CIF, and DDP terms with professional loading plans that optimize container weight and protect surface finishes. Real-time tracking is provided from factory gate to destination port.
