Description
Full-Range Square & Rectangular Tube Supply — From 20×20 mm to 500×500 mm in Q235B and Q355B grades, hot-rolled or galvanized, all backed by original mill test certificates.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Square and Rectangular Carbon Steel Tube |
| Product Type | Square / Rectangular Steel Tube (Hollow Section) |
| Steel Grade | Q195, Q215, Q235, Q235B, Q345, Q355, Q355B, S235JR, S355JR, SS400, STK400, ST42.2, ASTM A53 Grade A, ASTM A53 Grade B, ASTM A500 Grade A, ASTM A500 Grade B, ASTM A500 Grade C, ASTM A36, S195, EN10219, EN10210 |
| Standard | EN10219, EN10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A53, ASTM A36 |
| Section Shape | Square, Rectangular, Round |
| Size Range (Square) | 20×20 mm – 500×500 mm |
| Size Range (Rectangular) | 20×40 mm – 300×500 mm |
| Wall Thickness | 1.2 mm – 20 mm |
| Length | 3 m – 12 m (random or fixed) |
| Technique | Hot Rolled / ERW (Welded) |
| Surface Treatment | Hot Rolled, Pre-galvanized (Zinc coating 40–80 g/m²), Hot-dipped galvanized (Zinc coating 200–600 g/m²) |
| Tolerance | ±1% |
| Ends | Plain |
| Invoicing | By Actual Weight |
| Application | Construction, Steel structure engineering, Solar power support structures, Machinery manufacturing, Fence posts, Greenhouse frames, Shipbuilding, Power engineering, Highway railings, Bridges, Pressure vessels, Oil storage tanks |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Building | High-rise building frames, industrial warehouse columns, mezzanine floor supports |
| Steel Structure Engineering | Portal frame structures, truss members, bracing tubes for factories and hangars |
| Solar & Renewable Energy | Solar panel mounting racks, ground screw piles, greenhouse skeleton tubes |
| Infrastructure & Civil Works | Highway guardrail posts, bridge handrail uprights, street lighting poles |
| Machinery & Equipment | Conveyor frame sections, crane boom extensions, hydraulic cylinder sleeves |
| Shipbuilding & Marine | Deckhouse framing, non-structural bulkhead stiffeners, equipment support brackets |
Where Grade Equivalence Between GB, EN, and ASTM Costs You Time and Money
Buyers lose weeks chasing cross-reference tables that mills and traders never agree on.
I have watched procurement teams stall for months because their engineer specified Q355B, the European consultant wrote S355JR, and the American EPC insisted on ASTM A500 Grade C. Each party assumed the other was wrong. In reality, these grades overlap in yield strength and chemistry — but only if you map them correctly. Without a certified equivalence sheet, customs brokers flag mismatched documents, and site inspectors reject material before a single tube is welded. [NEED_CITE: steel grade equivalence mapping between GB, EN, and ASTM standards]
On top of that, wall-thickness tolerance is where margins hide. A supplier quoting by theoretical weight with heavy negative tolerance can look ten percent cheaper on paper, yet deliver less steel per meter than your structural calculation assumed. We invoice by actual weight and hold ±1% tolerance so the tonnage you pay for is the tonnage that arrives.
How These Hollow Sections Fit Structural and Solar Frame Loads
Square and rectangular tubes in Q235B and Q355B grades carry bending and compression loads efficiently because their closed section resists torsion better than open profiles. For solar mounting structures, the 1.2–3.0 mm wall range in pre-galvanized finish gives enough corrosion resistance for twenty-year outdoor exposure without the cost of hot-dipped coating. When the same Q235B Q355B square and rectangular steel tube supplier moves to heavy industrial frames, 6–20 mm walls in hot-rolled black condition accept full-penetration welding on site without zinc fume complications.
Meeting EN 10219, ASTM A500, and GB/T 6728 on the Same Project
Multi-national EPC projects often require tubes certified to more than one standard simultaneously. A bridge contractor in Southeast Asia may need JIS G3466 for handrails yet ASTM A500 Grade B for main trusses — sourced from the same mill heat to keep chemistry consistent. We produce to EN10219, EN10210, GB/T 6728, JIS G3466, and ASTM A500 / A53 on the same rolling line, then issue separate test certificates per standard. CE marking under EN10210 / EN10219 clears European customs; ASTM documentation satisfies North American specifiers. [NEED_CITE: EN 10219 cold-formed structural hollow section compliance requirements]
Steel Grade Selection: Q235B vs Q355B and Their International Counterparts
Q235B sits at the mild-steel end of the Chinese grade series, roughly matching S235JR in the European EN system and ASTM A36 / A53 Grade B in the American system. Its lower carbon equivalent makes it easier to weld on site without preheat, which suits general construction frames and fence posts. Q355B steps up in yield strength, aligning with S355JR and ASTM A500 Grade C, and is specified where member sizes must stay slim under higher loads — typical in long-span warehouse roofs and solar tracker supports. The ERW welding process used for these tubes produces a clean internal bead that does not interfere with bolted or welded connections, while hot-rolled versions offer superior corner radii for heavy structural work.
Surface treatment choice follows the exposure environment. Hot-rolled black tubes suit indoor or painted structures. Pre-galvanized coating at 40–80 g/m² protects during transport and short-term outdoor storage. Hot-dipped galvanized at 200–600 g/m² is specified for coastal solar farms, highway guardrails, and greenhouse frames where decades of atmospheric corrosion resistance are required. [NEED_CITE: hot-dip galvanized zinc coating weight and corrosion protection service life]
The Hidden Price of Accepting Negative Tolerance and Forged Certificates
When a supplier delivers Q355B tubes that are actually Q235B chemistry, or wall thickness falls below the ±1% tolerance band, the structural engineer’s load calculations no longer match the as-built member. Deflection increases, connection welds are overloaded, and the building may fail final inspection. Worse, if the mill test certificate cannot be traced to a real heat number, the entire batch becomes unsellable scrap at the port. [NEED_CITE: consequences of non-conforming steel hollow sections in structural engineering]
Why Procurement Teams Choose Our Hollow Section Division
We roll square and rectangular tubes from 20×20 mm up to 500×500 mm in-house, so there is no broker margin between your order and our mill price. Every heat is tested in our own laboratory before release — chemical composition, tensile strength, and flattening tests are recorded on the original mill test certificate with full heat-number traceability. Our catalog covers over 2800 dimension combinations across Q195 to Q355 grades, meaning you source both light-gauge solar tubes and heavy structural sections from one purchase order. Custom cut-to-length, punching, and bending are done before shipping, reducing your site labor. We hold ISO 9001:2015 certification, CE marking per EN10219 and EN10210, and accept SGS or BV third-party inspection at your request. Loading is handled by our own heavy-cargo team using open-top containers and flatbed trailers, with complete export documentation prepared in advance.
Documentation & Compliance
- Mill test certificate documenting Q235B or Q355B chemical composition, yield strength, and tensile properties per EN10219 / ASTM A500 / GB/T 6728
- CE certificate confirming EN10210 and EN10219 compliance for European Union market entry
- ISO 9001:2015 quality management system certificate covering production and inspection processes
- SGS or BV third-party inspection report available before container sealing, covering dimensional and surface checks
- Full material traceability by heat number linking each tube bundle to its original slab and rolling record
- Export customs documents including packing list, bill of lading, and certificate of origin matching the declared steel grade
Packaging, Loading & Delivery
- Hot-rolled Q235B and Q355B square tubes bundled with steel strips and waterproof wraps, labeled with heat number and grade at both ends
- Pre-galvanized and hot-dipped galvanized rectangular tubes packed with edge protectors to prevent zinc coating damage during ocean transit
- 6 m and 12 m fixed-length tubes loaded in open-top containers with timber chocks to prevent shifting; 3 m random lengths bundled for 20 ft standard containers
- Cut-to-size tubes under 3 m packaged on steel pallets with plastic corner guards for air freight or LCL shipment
- Every bundle marked with steel grade, size, heat number, and purchase order reference for site identification
- FOB, CIF, and DDP terms available with door-to-door tracking for project sites in Southeast Asia, Middle East, Africa, and South America
Send Your Drawings and Get a Certified Quote
Upload your section schedule with steel grade, wall thickness, length, and destination port. We return a detailed quotation with material cost, processing fees, and shipping terms within twelve hours, along with a sample mill test certificate so your engineer can verify compliance before placing the order.
Start Your Square and Rectangular Tube Order Today
Share your specification list and destination to receive pricing and original mill test certificates. Contact Shandong Xin Jiyuan Special Steel Tube Co., Ltd at admin@xjyplate.com or WhatsApp +86 188 5315 7756.
Frequently Asked Questions
Q: How do Q235B, S235JR, and ASTM A53 Grade B compare in chemical composition and strength?
A: These three grades are considered equivalent for most structural applications. Q235B is the Chinese GB/T 700 standard grade, S235JR follows the European EN 10025 system, and ASTM A53 Grade B is the American specification. All three share similar carbon and manganese ranges and deliver comparable yield strength for general construction and frame structures.
Q: Can you provide mill test certificates and arrange third-party inspection before shipment?
A: Yes. Every shipment includes an original mill test certificate showing chemical composition, mechanical properties, and heat number. We also accept SGS or BV third-party inspection at the loading port at the buyer’s request, with the inspection report issued before the container is sealed.
Q: What is the minimum order quantity for custom cut-to-size square and rectangular tubes?
A: The minimum order is 1 Ton. We can cut tubes to your required length from the 3 m to 12 m range, and process non-standard dimensions for square sections from 20×20 mm to 500×500 mm and rectangular sections from 20×40 mm to 300×500 mm.
Q: Should I choose pre-galvanized or hot-dipped galvanized finish for outdoor solar mounting structures?
A: For solar mounting structures with a design life exceeding twenty years in coastal or industrial atmospheres, hot-dipped galvanized coating at 200–600 g/m² provides long-term corrosion protection. Pre-galvanized finish at 40–80 g/m² is suitable for inland installations or where the structure will be painted after assembly.
Q: How do you invoice — by theoretical weight or actual weight?
A: We invoice by actual weight. This means you pay for the steel that is physically delivered, eliminating the hidden cost of negative tolerance that occurs when suppliers charge by theoretical weight while delivering under-thickness material.
Get Your Q235B Q355B Hollow Section Quote with Mill Certificates
Send your size schedule, steel grade, and port to admin@xjyplate.com or WhatsApp +86 188 5315 7756 for pricing and original test certificates within twelve hours.
