Description
Black ERW Square & Rectangular Steel Tube Supplier — Direct mill production covering Q195–Q345 and S235–S355 grades with wall thickness from 0.8mm to 20mm, shipped to 50+ countries under full international certification.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q195-Q345 Black ERW Square & Rectangular Steel Tube |
| Product Type | Square and Rectangular Steel Tube (ERW Welded Hollow Section) |
| Steel Grade | Q195, Q215, Q235, Q345, 10#, 20#, Gr.A, Gr.B, Gr.C, S235, S275, S355, A36, SS400 |
| Standard | ASTM A500, EN 10219, EN 10210, JIS G3466, GB/T 6728 |
| Section Shape | Square / Rectangular |
| Size Range (Square) | 20×20mm – 400×400mm |
| Size Range (Rectangular) | 20×40mm – 300×500mm |
| Wall Thickness | 0.8 – 20mm |
| Length | 3 – 12m (customizable) |
| Technique | ERW (High-Frequency Welded) |
| Surface Treatment | Black / Oiled / Pre-Galvanized (30–150g/m²) / Hot Dipped Galvanized (220–260g/m²) / Painted (Varnish/Lacquer) / Bare |
| Tolerance | ±1% |
| Ends | Plain End / Bevel End / Groove End / Threaded / Flange Joint |
| Invoicing | By Theoretical Weight |
| Application | Construction structures / Steel structures / Scaffolding / Fence posts / Fire protection systems / Greenhouse frames / Low-pressure fluid transport / Irrigation / Handrails |
| MOQ | 25 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, bridge support structures, column and beam assemblies |
| Steel Structure Fabrication | Portal frames, truss members, purlin and girt systems |
| Scaffolding & Access | Scaffold uprights, ledger tubes, base jack extensions |
| Agricultural & Greenhouse | Greenhouse arch frames, irrigation pipe racks, livestock fencing posts |
| Fire Protection & MEP | Sprinkler riser supports, HVAC duct framing, cable tray structures |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A ±1% tolerance on a 20mm wall tube means the difference between passing structural inspection and failing it on site.
When procurement teams order ERW square and rectangular hollow sections for load-bearing frames, even minor deviation in wall thickness compounds across hundreds of members. A batch arriving with negative tolerance beyond the declared ±1% range forces re-engineering calculations, delays welding schedules, and in worst cases triggers rejection by the site supervising engineer [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements]. The black ERW square and rectangular steel tube supplier you choose must guarantee tolerance consistency across every heat — not just on the sample piece sent for approval.
How Q195–Q345 Grades Match Structural Load Requirements
Black ERW square and rectangular steel tube in Q195 through Q345 grades covers the full spectrum from light-duty framing to heavy structural columns. Q195 and Q215 serve non-critical applications such as greenhouse frames and temporary fencing where formability matters more than load capacity. Q235 remains the workhorse grade for general construction — equivalent to S235 in the EN system and A36 under ASTM, making cross-standard substitution straightforward when project specifications shift between regions [NEED_CITE: steel grade equivalence between GB, EN, and ASTM standards]. Q345 steps up for higher moment-resisting frames and bridge components where yield strength directly governs member sizing.
Engineering Compliance and Surface Protection Selection
Structural hollow sections used in load-bearing frames must conform to EN 10219 for cold-formed welded sections or EN 10210 for hot-formed profiles, depending on the forming route. ERW tubes produced under EN 10219 carry CE marking for EU market access — without this certification, customs authorities in member states will hold the shipment regardless of material quality [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 10219]. For projects in coastal or industrial corrosion environments, the choice between black oiled, pre-galvanized (30–150g/m²), and hot dipped galvanized (220–260g/m²) finishes determines service life before first maintenance. End treatments — plain, bevel, groove, threaded, or flange — are selected based on field connection methods: bevel ends for butt-welded joints, threaded ends for mechanical couplings in scaffolding systems.
ERW Process, Grade Systems, and Surface Treatment Logic
The ERW (Electric Resistance Welded) process uses high-frequency current to fuse the strip edges under pressure, producing a continuous longitudinal weld seam. This method suits square and rectangular profiles from 20×20mm up to 300×500mm with wall thickness reaching 20mm — a range that covers most architectural and structural applications without requiring seamless or SSAW alternatives. Grade selection follows three parallel systems: the Chinese Q-series (Q195–Q345), the European S-series (S235–S355), and the American ASTM grades (Gr.A/B/C). Q235 and S235 share similar yield strength thresholds; Q345 aligns with S355 for higher-load applications. Surface treatment selection depends on the corrosion environment: black or oiled finish suits indoor structural use with subsequent painting; pre-galvanized provides moderate protection for semi-exposed framing; hot dipped galvanized delivers long-term corrosion resistance for outdoor infrastructure and coastal installations. The ±1% dimensional tolerance ensures that theoretical weight invoicing aligns with actual structural performance — a critical factor when engineering calculations depend on declared section properties.
Hidden Costs of Sourcing from Unverified Suppliers
Purchasing structural hollow sections without verified mill test certificates creates risk that surfaces only during project inspection. Material that fails to meet the declared grade — say, Q235 tubes delivering actual chemistry closer to Q195 — will not pass third-party testing, forcing replacement at the contractor’s expense and delaying the critical path [NEED_CITE: consequences of non-conforming structural steel in construction projects]. Missing CE documentation blocks EU customs clearance entirely, leaving containers stranded at port while demurrage charges accumulate. Negative tolerance abuse — where actual wall thickness falls below the declared range — reduces load capacity without visible indication, creating structural safety liability that the engineer of record must answer for.
Why Procurement Teams Choose Our Mill Direct
We produce black ERW square and rectangular steel tube across 3 dedicated production lines covering 2,800+ specifications — meaning your non-standard sizes ship from existing tooling rather than requiring minimum production runs that delay delivery. Our in-house physical and chemical laboratory tests every heat for dimensional accuracy, mechanical properties, and chemical composition before release, with full mill test certificates issued per EN 10204 3.1. Full international certification — ISO 9001:2015, Lloyd’s CE under EN 10219/10210, Singapore FPC, and SGS/BV third-party verification — ensures customs clearance in EU, Middle East, and Southeast Asian markets without documentation disputes. Custom non-standard sizes, cutting to length, and professional container loading with anti-damage measures come standard on every order. We have exported to 50+ countries, serving construction companies, steel structure fabricators, and machinery manufacturers who require consistent quality across repeat orders.
Documentation & Compliance
- Mill test certificate documenting Q195–Q345 chemical composition and mechanical properties per GB/T 6728 and EN 10219
- CE certificate under EN 10219 / EN 10210 for structural hollow sections exported to EU member states
- ISO 9001:2015 quality management system certificate covering ERW welding and dimensional inspection processes
- SGS or BV third-party inspection report available for pre-shipment verification of wall thickness and surface treatment
- Full material traceability by heat number linking each bundle to its production and test records
- Export customs documents including packing list, bill of lading, and certificate of origin for destination clearance
Packaging, Loading & Delivery
- Black ERW tubes bundled with steel strips and edge protectors to prevent surface scratching during ocean transit
- Oiled or pre-galvanized surfaces wrapped with waterproof paper and plastic film to preserve coating integrity in humid climates
- Container loading optimized for 3–12m lengths with wooden chocks and steel cradles to prevent shifting and bending during transit
- Custom cutting to project-specified lengths available before shipment, reducing on-site waste and handling
- Heat number and grade markings stenciled on each bundle for site identification and traceability verification
- FOB, CIF, and DDP shipping terms available with professional loading plans issued for every container
How to Request a Quotation with Full Technical Documentation
Submit your required dimensions, steel grade, surface treatment preference, quantity, and destination port — we respond within 12 hours with unit pricing, lead time, and shipping terms. For non-standard sizes outside the 20×20mm to 300×500mm range, share your drawing or specification sheet and we confirm tooling availability and production timeline. Mill test certificates, CE documentation, and third-party inspection arrangements are confirmed at the quotation stage so no surprises arise at customs or site inspection.
Frequently Asked Questions
Q: How do I cross-reference Q235, S235, A36, and SS400 for the same project?
A: These grades share similar yield strength ranges and are widely accepted as equivalents in international construction projects. Q235 (GB/T 6728) aligns with S235 (EN 10219), A36 (ASTM A500), and SS400 (JIS G3466). We provide grade equivalence confirmation in our quotation so your engineer can approve substitution before ordering.
Q: What is the difference between black, oiled, pre-galvanized, and hot dipped galvanized finishes?
A: Black finish is bare steel suitable for indoor use or subsequent painting. Oiled finish adds a thin防锈 layer for short-term corrosion protection during storage and transit. Pre-galvanized (30–150g/m²) offers moderate protection for semi-exposed applications. Hot dipped galvanized (220–260g/m²) provides long-term corrosion resistance for outdoor and coastal environments.
Q: Can I order non-standard dimensions outside the listed size range?
A: Yes. We produce custom non-standard sizes across our 2,800+ specification range. Share your required dimensions and we confirm tooling availability, MOQ, and production lead time.
Q: What certification documents do I need for EU customs clearance?
A: EU imports require CE marking under EN 10219 (cold-formed) or EN 10210 (hot-formed) for structural hollow sections. We provide CE certificates, mill test certificates per EN 10204 3.1, and can arrange SGS/BV third-party inspection if required by your project specification.
Q: How is theoretical weight calculated and does negative tolerance affect invoicing?
A: Invoicing is based on theoretical weight calculated from declared dimensions and standard steel density. Our ±1% tolerance guarantee ensures actual dimensions stay within the declared range, so theoretical weight invoicing reflects true material delivered.
Send Your Specifications for Pricing and Mill Test Certificate Review
Share your size, grade, quantity, and destination — we return a detailed quotation with unit pricing, lead time, and full documentation confirmation within 12 hours.
Contact: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjypipe.com
Website: www.sdxjypipe.com
