Description
Factory-Direct Q235 Q345 Q355 Carbon Steel Square Rectangular Tube — 2,800+ cross-section and wall-thickness combinations roll out of our three production lines in Jinan, shipped to greenhouse operators and steel structure fabricators across 50+ countries.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235 Q345 Q355 Carbon Steel Square Rectangular Tube |
| Product Type | Square and Rectangular Steel Tube |
| Steel Grade | Q195, Q215, Q235, Q245, Q345, Q355, SGCC, DX51D |
| Standard | ASTM, GB, BS, EN, DIN |
| Section Shape | Square / Rectangular |
| Size Range | 30×30 mm – 200×400 mm |
| Wall Thickness | 1.5 mm – 12 mm |
| Length | 1 m – 12 m |
| Technique | ERW / Seamless |
| Surface Treatment | Black / Galvanized |
| Tolerance | ±1% |
| Ends | Plain (non-oiled or as required) |
| Processing Service | Welding, Punching, Cutting, Bending, Decoiling |
| Application | Steel Structure, Curtain Wall, Greenhouse, Indoor Structural Frame |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Greenhouse Construction | Main load-bearing columns, roof purlins, side-wall framing for vegetable and flower greenhouses |
| Steel Structure Engineering | Portal frame columns, beam-to-column connections, mezzanine supports |
| Curtain Wall & Facade | Vertical mullions, horizontal transoms, architectural framing behind glass panels |
| Industrial Construction | Conveyor support structures, equipment platforms, warehouse racking uprights |
What Negative Wall Tolerance Costs on a Greenhouse Frame Order
A 0.6 mm shortfall on a 3 mm specified wall can turn a wind-rated greenhouse into a collapse claim.
Procurement teams ordering Q235 or Q345 carbon steel square rectangular tube for greenhouse projects often discover the damage only after the first typhoon season. Material shipped at the lower edge of negative tolerance looks identical on the mill test certificate but deflects noticeably under combined wind and crop load. The structural engineer then demands re-analysis, the contractor demands replacement tubes, and the project schedule collapses. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements]
Beyond the structural risk, inconsistent wall thickness creates welding problems on site — thin sections burn through while adjacent joints remain unfused, forcing rework that delays the entire erection sequence.
Matching Cross-Sections to Greenhouse Load Paths
Greenhouse frames carry a deceptively complex load combination: dead weight of glazing, live load from maintenance access, wind pressure on large flat surfaces, and in snow-prone regions, asymmetric snow drift. The 30×30 mm to 100×100 mm square sections in Q235 grade typically serve as purlins and side-wall bracing, while 100×50 mm to 200×100 mm rectangular sections in Q345 or Q355 grade handle the main portal frame columns and rafters. Our production lines cover every one of these sizes in a single order, so the structural engineer does not need to split the bill of materials across three suppliers.
Structural Codes, Surface Protection, and Customs Reality
Greenhouse structures in Southeast Asia, the Middle East, and South America must satisfy local adoption of EN 1993 or AISC 360, which reference hollow section dimensions and tolerances from EN 10219 or ASTM A500 respectively. [NEED_CITE: steel grade equivalence between EN 10219 and ASTM A500] Galvanized surface treatment is specified wherever relative humidity stays above 70% or where fertilizer vapors accelerate corrosion — the zinc layer must survive ocean transit without white rust, which demands proper passivation and bundled packaging. For EU-bound shipments, the CE mark under EN 10219 is not optional; customs authorities in Rotterdam and Hamburg routinely hold hollow sections lacking the Declaration of Performance.
Reading the Steel Grade Ladder: Q235, Q345, Q355
The Q-series designation follows the Chinese GB standard, where the number indicates the minimum yield strength in MPa. Q235 serves general structural work where loads are moderate — greenhouse purlins, handrails, non-critical bracing. Q345 and Q355 step up the yield strength for main frames, crane beams, and any member where deflection limits govern the design. When a project specification calls for ASTM A500 Grade B or C, or EN 10219 S275 or S355JR, the equivalent Q-grade can be supplied against the same mill test certificate, provided the chemical composition and mechanical properties are cross-referenced correctly. [NEED_CITE: carbon steel grade equivalence table covering GB, ASTM, and EN systems]
ERW (Electric Resistance Welded) process suits the majority of greenhouse and structural applications — the weld seam is forged under heat and pressure, producing a joint that matches the parent metal in strength. Seamless tubes, produced by piercing a solid billet, are reserved for high-pressure or precision-machined applications where weld-seam integrity cannot be tolerated.
The Hidden Price of Unverified Material
Buying carbon steel square rectangular tube on price alone, without independent verification of wall thickness and chemistry, transfers risk to the project timeline and the structure’s service life. A shipment that arrives with wall thickness below the specified tolerance fails dimensional inspection at the port, triggering re-export or scrap costs that dwarf the original price saving. Missing or forged mill test certificates block customs clearance in regulated markets — the container sits at the terminal accumulating demurrage while the buyer scrambles for replacement paperwork. Structural members that fail to meet the specified grade force the engineer to downgrade the allowable load, which can invalidate the original design and require costly reinforcement. [NEED_CITE: consequences of non-conforming steel hollow sections in structural projects]
Why Project Teams Source This Tube From Our Jinan Mill
Our Jinan facility operates three dedicated production lines covering square and rectangular sections from 30×30 mm up to 200×400 mm in wall thicknesses from 1.5 mm to 12 mm — every size in your bill of materials rolls off the same floor, under one quality system. The in-house physical and chemical laboratory tests every heat for composition, yield strength, tensile strength, and elongation before the material is released, and the mill test certificate travels with the shipment. We hold ISO 9001:2015, CE certification under EN 10210 and EN 10219, Singapore FPC, and third-party verification from SGS and BV — documents that satisfy customs and consultants in the EU, North America, and the Middle East. Custom non-standard sizes, cut-to-length, and punched or welded processing are handled in-house, so the material arrives on site ready to erect. Professional container loading with anti-damage measures prevents the bending and surface scratching that plague poorly packed tube shipments.
Documentation & Compliance
- Mill test certificate documenting Q235, Q345, or Q355 chemical composition and mechanical properties per GB/T 6728 or equivalent EN 10219 standard
- CE certificate and Declaration of Performance covering EN 10219 cold-formed structural hollow sections for EU customs clearance
- ISO 9001:2015 quality management system certificate covering the full production process from raw material to finished tube
- SGS or BV third-party inspection report verifying dimensional tolerance, surface quality, and wall thickness on request
- Heat number traceability linking each bundle to its original slab chemistry and rolling record
- Export documentation including packing list, bill of lading, and certificate of origin for destination-country import clearance
Packaging, Loading & Delivery
- Q235, Q345, and Q355 carbon steel square rectangular tube bundled with high-tensile steel strips at no more than six points per bundle, with end caps to prevent edge damage during handling
- Galvanized tubes wrapped with waterproof paper and edge protectors to preserve the zinc coating against condensation and salt spray during ocean transit
- Mixed-size container loading planned against the 1–12 m length range to maximize 20ft and 40ft payload, with heavier rectangular sections placed at the bottom and lighter square sections on top
- Cut-to-length service available for 6 m and 12 m standard lengths, with saw-cut ends deburred and marked with heat number, steel grade, and section dimensions
- FOB, CIF, and DDP terms available from Qingdao port, with door-to-door forwarding to major construction hubs across Southeast Asia, the Middle East, and South America
Getting Your Quotation and Mill Test Certificate Ready
Send your bill of materials — section dimensions, wall thickness, steel grade, surface treatment, total tonnage, and destination port — and our team returns a detailed offer within 12 hours, including unit price, production lead time, and the mill test certificate template for your consultant’s review. For non-standard sizes outside the 30×30 mm to 200×400 mm range, we confirm tooling availability and minimum order quantity before the commercial offer is issued.
Frequently Asked Questions
Q: Can you supply Q235, Q345, and Q355 tubes against ASTM A500 or EN 10219 standards on the same order?
A: Yes. Our in-house laboratory cross-references the chemical composition and mechanical properties of Q-series grades to their ASTM A500 and EN 10219 equivalents, and the mill test certificate documents compliance with whichever standard your project specification requires.
Q: What is the minimum order quantity for custom non-standard sizes?
A: The standard MOQ is 1 Ton. For non-standard cross-sections or wall thicknesses outside the 30×30 mm to 200×400 mm / 1.5–12 mm range, we confirm the minimum tonnage per size after reviewing the drawing.
Q: Do you provide third-party inspection before shipment?
A: Yes. SGS and BV inspection reports covering dimensional tolerance, surface quality, wall thickness, and mechanical properties can be arranged at any stage of production, with the report issued before the container is sealed.
Q: How do you protect galvanized tubes during ocean shipping?
A: Galvanized square and rectangular tubes are bundled with waterproof paper, edge protectors, and steel strips, then loaded with anti-damage measures to prevent zinc coating abrasion and white rust formation during transit.
Q: Can you cut, punch, or weld the tubes before delivery?
A: Yes. Our processing services include cutting to specified lengths, punching for bolt connections, welding for fabricated assemblies, and bending for curved structural members — all completed in-house before shipment.
Send Your Bill of Materials for a Detailed Offer
Share your section sizes, steel grade, surface treatment, quantity, and destination port, and receive a formal quotation with mill test certificate template within 12 hours.
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
