Description
Factory-direct square and rectangular tubes — Q235B and Q355B hollow sections shipped with original mill test certificates and EN10219/ASTM A500 equivalence mapping.
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, Q345(Q355), #20, #45, S235JR, S355JR, S355J2, SS400, STK400, ST42.2, ASTM A53 Grade A/B, ASTM A500 Grade A/B/C, ASTM A36, EN10219, EN10210, JIS G3466 |
| 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; Rectangular: 20×40 mm – 300×500 mm |
| Wall Thickness | 0.5 – 30 mm (structural range 1.2 – 20 mm) |
| Length | 3 – 12 m (random / cut-to-size) |
| Technique | Hot Rolled / ERW (Welded) |
| Surface Treatment | Black (Hot Rolled) / Pre-galvanized (40–80 g/m²) / Hot-dip galvanized (200–600 g/m²) |
| Tolerance | ±1% |
| Ends | Plain / Beveled (as required) |
| Application | Construction / Building structures / Steel structure engineering / Solar mounting structures / Machinery manufacturing / Shipbuilding / Fence posts / Greenhouse frames / Highway railings / Power engineering / Pressure vessels / Oil storage tanks / Bridges / Airport facilities |
| MOQ | 1 Ton |
| Origin | China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Steel Fabricators & Construction | Building columns, portal frames, bridge railings, heavy equipment bases |
| Solar EPC Contractors | Mounting structure tubes in pre-galvanized or hot-dip galvanized finish |
| Machinery & Greenhouse Manufacturers | Standard SHS/RHS frames for greenhouse skeletons, conveyor supports, machine guards |
| Shipbuilding & Marine | Non-pressure structural members, deck supports, handrail posts |
| Infrastructure & Power | Highway guardrail posts, airport facility frames, power transmission tower bracing |
What Negative Tolerance Really Costs on a Structural Frame Order
A 0.8 mm wall deviation on a 5 mm SHS means 15% less load capacity — and a rejected shipment at destination.
I once watched a Dubai contractor’s inspector pull a caliper on a 100×100×5 mm carbon square tube and read 4.2 mm. The entire 20ft container was flagged. We absorbed replacement costs from our own margin that cycle. Hidden negative tolerance is the single most expensive mistake in hollow section procurement — it does not show up until the steel reaches the job site, at which point re-melting, re-shipping, and re-fabrication multiply the original price several times over [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed hollow sections]. Grade confusion between GB, EN, and ASTM systems creates a parallel failure mode: a buyer orders Q355B expecting S355JR equivalence, receives material with mismatched chemistry, and fails third-party inspection before the container even leaves the port.
How These Hollow Sections Match Structural Frame Requirements
Q235B and Q355B square and rectangular steel tubes cover the yield range that structural engineers specify for portal frames, building columns, and bridge railings across Asia, the Middle East, and South America. The ±1% wall-thickness tolerance, invoiced by actual weight, means the load calculations your engineer stamps are the load the steel actually carries — no hidden negative tolerance eroding safety factors at the connection node. For solar mounting and greenhouse applications, pre-galvanized and hot-dip galvanized finishes resist corrosion without field painting, and the 1 Ton MOQ lets EPC contractors trial a single container before committing to volume.
Engineering Compliance and Certification Pathways
Structural hollow sections must satisfy the dimensional and mechanical requirements of the standard specified in the project contract — EN10219 for European projects, ASTM A500 for North American work, GB/T 6728 for domestic Chinese construction, and JIS G3466 for Japanese-spec infrastructure [NEED_CITE: steel grade equivalence mapping between GB Q-series, EN S-series, and ASTM A500]. CE certification under EN10210 and EN10219 is mandatory for structural steel entering the EU market; without it, customs holds the shipment regardless of material quality. For corrosive environments — coastal solar farms, chemical plant walkways, marine deck structures — the choice between pre-galvanized (40–80 g/m²) and hot-dip galvanized (200–600 g/m²) determines service life before first maintenance. Cut-to-size lengths of 3–12 m reduce on-site welding and secondary cutting waste.
Steel Grade Selection and Manufacturing Process Logic
Q235B delivers adequate strength for general structural frames and fence posts at the lowest cost point; Q355B (equivalent to S355JR / ASTM A500 Grade B) steps up yield strength for heavier portal frames, bridge components, and crane runways where deflection limits tighten. The ERW welding process produces a continuous longitudinal seam suited to square and rectangular profiles up to 500×500 mm, while hot-rolled production covers the heavier wall range up to 30 mm where seamless or SSAW processes would be economically unjustified for non-pressure applications. Surface treatment selection follows environment: black hot-rolled tubes serve indoor structural frames where painting or fireproofing follows; pre-galvanized tubes suit semi-exposed structures like greenhouse frames; hot-dip galvanized tubes handle fully exposed or corrosive conditions without field coating. Wall-thickness tolerance of ±1% with actual-weight invoicing eliminates the commercial distortion of theoretical-weight billing, where buyers pay for steel that is not there [NEED_CITE: negative tolerance practices in steel tube trade and their impact on structural integrity].
Hidden Costs When Material Traceability Breaks Down
Ordering Q235B square and rectangular steel tubes without verified mill test certificates exposes the project to four failure modes: customs rejection at destination port when CE or ASTM documentation is missing; structural inspection failure when heat numbers cannot be traced to chemical composition reports; load calculation invalidation when actual wall thickness deviates beyond ±1% tolerance; and re-fabrication costs when cut-to-size lengths arrive off-spec. Each of these failures multiplies the original material cost — and none of them are visible until the steel reaches the job site or the inspector’s table [NEED_CITE: EN 10219 cold-formed hollow section dimensional and mechanical requirements].
Why Procurement Teams Source These Tubes from XJY Plate
Every Q235B and Q355B square and rectangular steel tube leaving our facility carries an original mill test certificate with heat number, chemical composition, and mechanical properties — full traceability from slab to finished section. We map grade equivalence across GB, EN, ASTM, and JIS systems so that a Q355B order for a European project ships with EN10219 certification and S355JR documentation without the buyer managing multiple suppliers. Custom cutting, leveling, and punching reduce on-site secondary work, and our 1 Ton MOQ allows trial orders before volume commitment. Professional heavy-cargo loading — flatbed, open-top container, and break-bulk — with nylon sling protection prevents surface damage to galvanized coatings during ocean transit. ISO 9001:2015 and CE certification, plus SGS/BV third-party inspection availability, satisfy the most stringent project specification requirements.
Documentation & Compliance
- Mill test certificate documenting Q235B or Q355B chemical composition, yield strength, and tensile properties per GB/T 6728 or EN10219
- CE certificate covering EN10210 and EN10219 structural hollow sections for EU market entry
- ISO 9001:2015 quality management certificate for manufacturing and supply processes
- SGS or BV third-party inspection report available before shipment for project-specified quality verification
- Material traceability by heat number linking each bundle to its original mill test certificate
- Customs documentation including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Q235B and Q355B square and rectangular tubes bundled with steel strips and edge protectors to preserve surface finish during transit
- Pre-galvanized and hot-dip galvanized tubes wrapped with waterproof paper and plastic sleeves to prevent white rust formation during ocean shipment
- Cut-to-size lengths of 3–6 m loaded in 20ft containers; 6–12 m lengths in 40ft open-top containers with proper weight distribution
- Heat number and steel grade stenciled on each bundle for site identification and traceability verification
- FOB, CIF, and DDP shipping terms available with professional flatbed and break-bulk logistics for heavy structural sections
Ready to Lock in Your Specification
Submit your steel grade, section dimensions, wall thickness, quantity, and destination port — we respond within 12 hours with a detailed quotation, mill test certificate preview, and loading plan. Non-standard sizes, custom cutting, and third-party inspection arrangements are confirmed before the deposit is paid.
Get Your Q235B Q355B Square Rectangular Steel Tube Quote with Mill Test Certificate
Send your specification to admin@xjyplate.com or contact us via WhatsApp at +86 188 5315 7756.
Frequently Asked Questions
Q: How do Q235B and Q355B map to EN and ASTM steel grades?
A: Q235B is equivalent to S235JR (EN10219) and ASTM A53 Grade B; Q355B is equivalent to S355JR (EN10219) and ASTM A500 Grade B/C. We provide a full grade equivalence chart with every inquiry so your engineer can verify compliance with the project specification.
Q: Can I verify material authenticity before the container is sealed?
A: Yes. We provide original mill test certificates with heat numbers, chemical composition, and mechanical properties before or with shipment. SGS or BV third-party inspection is available at our facility before loading, and the inspection report is included in the shipping documentation.
Q: What is the minimum order quantity for non-standard sizes?
A: The standard MOQ is 1 Ton. Custom cut-to-size lengths, non-standard section dimensions, and special surface treatment requirements are available for trial orders, allowing fabricators and EPC contractors to validate material before committing to volume.
Q: How do you prevent galvanized coating damage during ocean shipment?
A: Pre-galvanized and hot-dip galvanized tubes are bundled with edge protectors, wrapped in waterproof paper and plastic sleeves, and loaded with nylon slings to prevent zinc coating abrasion. Our loading plans optimize container weight distribution for heavy structural sections.
Q: Do you invoice by theoretical weight or actual weight?
A: We invoice by actual weight. This eliminates the commercial distortion of negative tolerance practices, where buyers pay for steel that is not physically present in the bundle.
Request Your Q235B Q355B Square Rectangular Steel Tube Quotation
Submit your specification — steel grade, section size, wall thickness, quantity, and destination — to admin@xjyplate.com or WhatsApp +86 188 5315 7756 for a detailed quotation with mill test certificate preview within 12 hours.
