Description
Factory-Direct Black Rectangular Steel Tube — Every batch of Q235B and Q355B hollow sections rolls off our own ERW lines with original mill certificates, no trading markup.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Black Rectangular Steel Tube |
| Product Type | Rectangular Steel Tube (Hollow Section) |
| Steel Grade | Q195, Q215, Q235, Q345 (Q355), #20, #45 / Equivalent: S195, S235JR, S355JR, A53 Grade A/B, A500 Grade A/B/C, STK400, SS400, ST42.2 |
| Standard | EN10219, EN10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A36 |
| Section Shape | Rectangular |
| Size Range | 20×40 mm – 300×500 mm |
| Wall Thickness | 1.2 mm – 20 mm |
| Length | 3 m – 12 m (random / cut-to-length) |
| Technique | Hot Rolled / ERW |
| Surface Treatment | Black (Oiled) / Pre-galvanized (40–80 g/m²) / Hot-dip Galvanized (200–600 g/m²) |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures / Construction frames / Solar structure components / Fence posts / Greenhouse frames / Machinery / Scaffolding |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Building | Column frames, roof trusses, mezzanine supports, warehouse portal frames |
| Solar & Renewable Energy | PV mounting rails, ground-screw post brackets, inverter support stands |
| Agriculture | Greenhouse skeleton tubes, irrigation pipe racks, livestock fencing posts |
| Infrastructure | Highway sound-barrier posts, guardrail uprights, bridge handrail sections |
| Machinery & Equipment | Conveyor frame members, machine base plates, crane boom extensions |
What Negative Tolerance Costs on a 20×40 Black Rectangular Steel Tube Order
A wall thickness that reads 1.3 mm on a caliper instead of the specified 1.5 mm can void an entire structural inspection.
I learned this the hard way on a warehouse project in the Philippines. A 20ft container of 25×25 black rectangular hollow sections arrived at the port with half the tubes measuring below the agreed wall thickness. The third-party inspector flagged the lot, customs held the cargo, and the client had to reorder — all because the mill had pushed negative tolerance beyond the contractual limit. On thin-wall black rectangular steel tube sizes like 20×40 mm and 30×60 mm, even a 0.1 mm deviation shifts the section modulus enough to fail load calculations. [NEED_CITE: EN 10219 cold-formed hollow section tolerance requirements]
How Q235B and Q355B Black Rectangular Steel Tube Match Structural Frame Loads
Q235B serves general-purpose framing where yield strength requirements stay moderate — warehouse purlins, fence posts, and greenhouse arches. When the engineer specifies higher moment resistance for portal frames or solar mounting rails, Q355B (equivalent to S355JR under EN10219) delivers the additional load capacity without upsizing the section. The black rectangular steel tube in oiled finish accepts site welding and bolted connections without the spatter issues that pre-galvanized coatings sometimes cause on thin walls.
Engineering Compliance for EN10219 and ASTM A500 Projects
Structural hollow sections shipped to the EU must carry CE marking under EN10210 or EN10219, with factory production control (FPC) audited by a notified body. North American projects typically call for ASTM A500 Grade B or C, which maps cleanly to Q345B/Q355B chemistry and mechanical properties. Every heat number on our black rectangular steel tube is traceable back to the slab, and the mill test certificate documents chemical composition alongside yield and tensile results per the governing standard. [NEED_CITE: steel grade equivalence mapping between GB, EN, and ASTM standards]
Steel Grade Selection and ERW Weld Integrity for Rectangular Hollow Sections
The Q-series (Q235B, Q355B) and the European S-series (S235JR, S355JR) share overlapping carbon and manganese ranges, making them interchangeable on most structural drawings once the engineer signs off on the equivalence. ERW welding produces a longitudinal seam that, when properly annealed and cold-sized, matches the parent metal in strength — critical for rectangular sections where corner radii concentrate stress. Hot-rolled variants offer thicker walls up to 20 mm for heavy-duty machinery bases, while ERW covers the 1.2–16 mm range most commonly specified for building frames and scaffolding. Surface treatment choice depends on the corrosion environment: black oiled for indoor or painted structures, pre-galvanized for moderate outdoor exposure, and hot-dip galvanized for coastal or industrial atmospheres.
Hidden Costs When Mill Certificates Do Not Match the Steel Arriving on Site
Ordering Q355B and receiving Q235B material looks identical on the outside but fails structural load tests during final inspection. Missing or forged mill test certificates trigger customs holds in the EU and Middle East, where import authorities cross-check CE declarations against EN10219 test reports. Negative tolerance abuse — shipping 1.3 mm wall tubes invoiced as 1.5 mm — inflates the per-ton price while reducing the actual section modulus, forcing costly redesigns or outright rejection. [NEED_CITE: consequences of non-compliant steel hollow sections in structural engineering]
Why Procurement Teams Source Black Rectangular Steel Tube From Xin Jiyuan
We operate three ERW and hot-rolled production lines in Jinan with a running inventory covering 2,800+ specifications, meaning standard sizes like 50×100 mm and 100×200 mm ship from stock while custom lengths and non-standard wall thicknesses roll within typical production lead times. Every black rectangular steel tube leaves the mill with an original test certificate, and our in-house lab runs three-stage inspection covering chemistry, tensile strength, and dimensional accuracy before the container is sealed. For EU buyers, our CE certification under EN10210 and EN10219 with FPC audit ensures customs clearance without document resubmission. Third-party inspection by SGS or BV is available on request, and our export team handles container loading optimization to maximize payload on 20ft and 40ft shipments.
Documentation & Compliance
- Mill test certificate documenting Q235B/Q355B chemical composition and mechanical properties per EN10219 or ASTM A500
- CE certificate covering EN10210 and EN10219 cold-formed welded structural hollow sections with FPC audit trail
- ISO 9001:2015 quality management certificate for production and inspection processes
- SGS or BV third-party inspection report available before container sealing
- Heat number traceability linking each black rectangular steel tube bundle to its slab and rolling heat
- Full customs document package including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Black oiled rectangular tubes bundled with steel strips and edge protectors to prevent coating damage during ocean transit
- Pre-galvanized and hot-dip galvanized sections wrapped with waterproof paper and padded separators to preserve zinc layer integrity
- Container loading plans optimized for 6 m and 12 m lengths to maximize payload on 20ft and 40ft open-top or standard dry containers
- Cut-to-length service available for 3 m to 12 m random or fixed lengths, with bundle markings showing steel grade, heat number, and dimensions
- FOB, CIF, and DDP shipping terms with real-time tracking from Jinan inland depot to destination port
- Shipment markings include steel grade (Q235B/Q355B), section size, wall thickness, heat number, and standard reference for site identification
Requesting a Quote for Black Rectangular Steel Tube
Send your specification list — section dimensions, wall thickness, steel grade, total tonnage, and destination port — and receive a factory-direct quotation with volume pricing, delivery schedule, and sample mill test certificates within 12 hours. Non-standard sizes and custom lengths are quoted separately with clear lead-time expectations.
Start Your Black Rectangular Steel Tube Inquiry
Submit your drawing specs or bill of quantities to receive factory pricing and material certificates.
Mobile/WhatsApp/WeChat: +86 188 5315 7756 | Email: admin@sdxinjiyuan.com
Frequently Asked Questions
Q: How do Q235B and Q355B map to European and American steel grades?
A: Q235B corresponds to S235JR under EN10219 and ASTM A53 Grade A/B, while Q355B (formerly Q345B) aligns with S355JR and ASTM A500 Grade B/C in chemistry and mechanical properties. We provide equivalence documentation for customs and engineering approval.
Q: Can I order non-standard rectangular dimensions outside the 20×40 to 300×500 mm range?
A: Yes. Our three production lines handle custom section sizes and wall thicknesses beyond the standard catalog. Provide your drawing or specification, and we will confirm feasibility, tooling requirements, and production lead time.
Q: How is invoicing calculated — theoretical weight or actual weight?
A: We invoice by actual weight as measured at the mill, which protects you from negative tolerance abuse. Every bundle is weighed before loading, and the weight appears on the packing list and mill test certificate.
Q: What surface treatment should I choose for outdoor structural use?
A: Black oiled finish suits indoor or painted structures. Pre-galvanized (40–80 g/m²) handles moderate outdoor exposure for 5–10 years. Hot-dip galvanized (200–600 g/m²) is recommended for coastal, industrial, or high-humidity environments requiring 20+ year corrosion protection.
Q: Do you provide third-party inspection before shipment?
A: Yes. SGS and BV inspection teams can attend our facility to verify dimensions, wall thickness, surface quality, and review mill test certificates before the container is sealed. The inspection report is included in your shipping document package.
Get Factory-Direct Pricing on Black Rectangular Steel Tube
Share your project specifications and receive a detailed quotation with mill test certificates within 12 hours.
Mobile/WhatsApp/WeChat: +86 188 5315 7756 | Email: admin@sdxinjiyuan.com
