Description
Full-Range Welded Square & Rectangular Tubes — 20×20 mm to 500×500 mm in Q195–Q355 grades, pre-galvanized or hot-dip galvanized, produced to EN 10219 / ASTM A500, ready for structural and infrastructure projects worldwide.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Welded Carbon Steel Square & Rectangular Pipe |
| Product Type | Welded Carbon Steel Square / Rectangular Pipe (Hollow Section) |
| Steel Grade | Q195, Q215, Q235, Q345 (Q355), #20, #45; Equivalent: S195 / S235JR / S355JR / S355J2 / A53 Grade A / A53 Grade B / A500 Grade A / A500 Grade B / A500 Grade C / STK400 / SS400 / ST42.2 |
| Standard | EN 10219, EN 10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A53, ASTM A36 |
| Section Shape | Square / Rectangular |
| Size Range | Square: 20×20 mm – 500×500 mm; Rectangular: 20×40 mm – 300×500 mm |
| Wall Thickness | 1.2 mm – 20 mm |
| Length | 3 m – 12 m (random / customized) |
| Technique | Hot Rolled / Welded (ERW) |
| Surface Treatment | Pre-galvanized (Zn 40–80 g/m²) / Hot-dip galvanized (Zn 200–600 g/m²) / Black (oiled or non-oiled) |
| Tolerance | ±1% (wall thickness) |
| Ends | Plain / Beveled (per customer requirement) |
| Processing Service | Bending, Welding, Decoiling, Punching, Cutting |
| Application | Construction, steel structures, solar mounting, fencing, greenhouse, machinery, shipbuilding, highway railings, bridges |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Building | High-rise building frames, industrial warehouse columns, mezzanine beams |
| Solar & Renewable Energy | Solar panel mounting structures, ground-screw bases, inverter support frames |
| Infrastructure | Highway guardrail posts, bridge handrail supports, noise barrier frames |
| Agriculture | Greenhouse skeleton tubes, irrigation pivot frames, livestock fencing posts |
| Machinery & Equipment | Conveyor roller frames, crane boom sections, machine base supports |
Where Grade Equivalence Failures Delay Customs and Site Acceptance
Misdeclared steel grades trigger port holds, third-party re-inspection fees, and on-site rejection — costs that dwarf the material price difference.
Procurement teams sourcing welded square tubes across regions constantly hit the same wall: a drawing calls for S235JR per EN 10219, the mill ships Q235B per GB/T 6728, and nobody on site can prove they are interchangeable. Customs officers in the EU or Middle East do not accept verbal assurances. [NEED_CITE: steel grade equivalence between EN 10219 and ASTM A500 standards] When the mill test certificate lists a Chinese grade without cross-reference to the project-specified EN or ASTM designation, the entire batch sits in a bonded warehouse until a re-inspection agency confirms chemical and mechanical compliance — or rejects it outright.
Beyond grade confusion, wall-thickness tolerance is the second silent budget killer. A supplier quoting “1.5 mm” but delivering 1.3 mm across the bundle passes the mill gate on negative tolerance, yet fails the engineer’s load calculation. Invoicing by theoretical weight hides the shortfall; invoicing by actual weight forces transparency. [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed hollow sections]
Matching Hollow Sections to Structural Load Paths and Connection Details
When a Q235B Q355B welded square rectangular steel tube supplier delivers sections for a solar mounting frame, the 50×50×3.0 mm posts must carry both vertical dead load and lateral wind uplift without buckling at the base plate weld. ERW welded hollow sections with ±1% wall-thickness tolerance ensure that the moment of inertia used in the engineer’s calculation matches what arrives on site. For coastal solar farms, hot-dip galvanized coating at 200–600 g/m² zinc provides corrosion resistance that outlasts the 25-year design life, while pre-galvanized tubes at 40–80 g/m² suffice for indoor machinery frames where appearance matters more than salt exposure.
Engineering Compliance Across EN, ASTM, and GB Frameworks
Structural engineers designing to EN 1993-1-1 or AISC 360 require hollow sections that meet specific dimensional and material standards. EN 10219 covers cold-formed welded structural hollow sections, while EN 10210 applies to hot-finished equivalents; ASTM A500 Grades A, B, and C govern the North American market. A Q235B Q355B welded square rectangular steel tube supplier must demonstrate that Q235 maps to S235JR (EN) and A53 Grade B (ASTM), while Q355 aligns with S355JR and A500 Grade B. [NEED_CITE: grade equivalence mapping between GB/T 6728 and EN 10219] CE marking under EN 10210 / EN 10219 is mandatory for structural steel entering the EU, and SGS or BV third-party inspection before loading satisfies most Middle East and African project specifications. Custom cutting to site-specific lengths — say 5.8 m instead of the standard 6 m — reduces on-site welding and scrap.
Understanding ERW Welding, Steel Grade Systems, and Surface Protection
The ERW (Electric Resistance Welding) process forms a continuous weld seam along the tube’s longitudinal axis by passing high-frequency current through the steel strip edges. This method suits square and rectangular hollow sections from 20×20 mm up to 500×500 mm with wall thicknesses from 1.2 mm to 20 mm, offering cost efficiency over seamless alternatives for non-pressure applications. Steel grade selection follows three parallel systems: the Chinese Q-series (Q195, Q235, Q355) where the number indicates minimum yield strength in MPa; the European S-series (S235JR, S355JR, S355J2) with Charpy impact requirements denoted by suffix letters; and the American ASTM system (A53, A500) organized by grade letters. Surface treatment choice depends on the service environment: black (oiled) tubes suit indoor structural frames where painting follows; pre-galvanized at 40–80 g/m² zinc covers light corrosion; hot-dip galvanized at 200–600 g/m² handles outdoor, industrial, or marine exposure. [NEED_CITE: hot-dip galvanizing coating thickness standards for structural steel] Wall thickness tolerance of ±1% means that a specified 4.0 mm wall measures between 3.96 mm and 4.04 mm — tight enough to satisfy structural calculations without the hidden negative tolerance traps that plague some supply chains.
The Real Cost of Accepting Unverified Tolerance and Missing Certificates
When a batch of 200×200×8.0 mm rectangular hollow sections arrives at a European construction site with wall thickness measuring 6.8 mm instead of the specified 8.0 mm, the structural engineer cannot approve the load-bearing columns. The material must either be downgraded to a non-structural use — losing its original value — or scrapped entirely. [NEED_CITE: consequences of dimensional non-compliance in EN 10219 structural applications] Missing mill test certificates mean no heat number traceability, no chemical composition verification, and no mechanical property confirmation. Customs authorities in countries requiring CE-marked structural steel will hold the shipment indefinitely without proper documentation. The hidden costs — demurrage, re-inspection fees, project delays, and replacement material shipping — routinely exceed the original purchase price by multiples.
Why Project Procurement Teams Consolidate Hollow Section Orders Here
Every Q235B Q355B welded square rectangular steel tube supplier claims quality, but our in-house metallurgical laboratory tests every heat for chemical composition and mechanical properties before release, generating original mill test certificates with full traceability. We maintain ready stock across the full 20×20 mm to 500×500 mm range in Q195 through Q355 grades, eliminating the minimum-order constraints that force buyers to over-purchase from mills. Custom processing — plasma cutting, bending, punching, and beveling — happens in our own facility, so a single order covers both standard sections and fabrication-ready pieces. CE certification under EN 10210 and EN 10219, ISO 9001:2015 quality management, and SGS/BV third-party inspection availability satisfy the most stringent project compliance requirements. Professional heavy-cargo logistics teams handle flatbed, open-top container, and break-bulk loading, ensuring that 12-meter tubes ship without damage or overweight penalties.
Documentation & Compliance
- Mill test certificate documenting Q235B or Q355B chemical composition, yield strength, and tensile properties per GB/T 6728 with EN 10219 / ASTM A500 equivalence noted
- CE certificate confirming EN 10210 and EN 10219 compliance for structural hollow sections entering European markets
- ISO 9001:2015 quality management system certificate covering production, inspection, and traceability processes
- SGS or BV third-party inspection report verifying dimensional accuracy, weld seam integrity, and coating thickness before container loading
- Material traceability by heat number linking each bundle to its original mill test certificate and production batch
- Customs documentation including commercial invoice, packing list, bill of lading, and certificate of origin formatted for destination-country clearance
Packaging, Loading & Delivery
- Pre-galvanized and hot-dip galvanized Q235B Q355B welded square rectangular steel tube bundles wrapped with waterproof paper and steel strips, with edge protectors preserving the zinc coating during ocean transit
- Black (oiled) tubes bundled in seaworthy packaging with anti-rust paper interleaving to prevent surface scratching between adjacent sections
- Container loading optimized for 3 m to 6 m lengths in 20-foot units and 6 m to 12 m lengths in 40-foot open-top containers, with wooden chocks preventing shift during transit
- Custom cut-to-length service available for 3 m – 12 m random or fixed lengths, reducing on-site cutting waste and welding time
- Each bundle labeled with heat number, steel grade (Q235B / Q355B), section dimensions, wall thickness, and bundle weight for immediate site identification
- Shipping terms FOB, CIF, or DDP with professional flatbed and break-bulk options for project cargo exceeding container capacity
How to Initiate Your Hollow Section Procurement
Submit your required steel grade (Q235B, Q355B, or equivalent), section dimensions, wall thickness, length, quantity, and destination port — we respond within 12 hours with a detailed quotation including material cost, any processing fees, and shipping terms. If your project specifies EN 10219 or ASTM A500 compliance, confirm the required certification and third-party inspection scope so we can include it in the contract. For non-standard dimensions or custom fabrication, share your drawings and we will provide a processing feasibility assessment alongside the material quote.
Request Your Quotation and Mill Test Certificate Today
Send your specifications to receive a detailed quotation with original mill test certificate preview and shipping plan within 12 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.xjyplate.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@xjyplate.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
