Our Q235 Square and Rectangular Black Steel Pipes are high-quality hollow structural sections widely used in construction, engineering, machinery, and fluid transportation systems. Based on the cross-sectional profile, square tubes can be categorized into:
Simple-section square tubes – square tubes and rectangular tubes
Complex-section square tubes – flower-shaped, open-section, corrugated, and customized special-shaped tubes
These hollow sections are manufactured with precision welding technology and strict quality control, ensuring excellent strength, uniform wall thickness, and reliable performance for diverse applications.
Product Information
Company: Gnee Steel
Product Name: Q235 Square / Rectangular / Round Black Welded Steel Pipe – Hollow Section from China
Size Range
Round OD: 12–762 mm
Thickness: 0.4–20 mm
Available Materials
Q195: Grade B, SS330, SPC, S185
Q215: Grade D, CS Type B, SS330, SPHC
Q235: Grade D, SS400, S235JR / S235JO / S235J2
Q345: SS500, ST52
Technology Options
Pre-galvanized
Hot-dip galvanized
Hang-planting galvanization
Zinc Coating: 20–600 g/m²
Surface Treatments
Bare
Black painted (varnish coating)
Galvanized
Oiled
3PE / FBE corrosion-resistant coating
Pipe Ends
Plain
Beveled
Threaded
With sockets, PVC caps, coupling, clamps
Customized upon request
Packaging
Bundles
Waterproof wrapping
Customized packing options
Applications
Liquid transportation: water, gas, pump wells
Construction pipes
Structural uses: greenhouses, fence posts, curtain wall frames
Mechanical components and general engineering
Order & Delivery
MOQ: 10 MT
Delivery Time: 10–30 days after deposit
Inspection Certification: ISO9001:2000, BV, SGS, Intertek
Additional Features
High-Frequency Welding Technology
All pipes are manufactured using advanced high-frequency welding (HFW) technology, ensuring stable weld quality, uniform seams, and superior mechanical performance.
Optional Weld Seam Removal
Both inner and outer weld beads can be removed according to customer requirements, resulting in a smoother internal surface and improved flow efficiency for fluid applications.
Customizable Shapes and Specifications
Special shapes, non-standard dimensions, and tailored hollow section profiles are available to meet unique design or engineering needs.
Necking, Expanding, and Hole Punching Services
Pipes can be necked down, expanded, slotted, or punched with holes for structural, mechanical, or assembly requirements.
Third-Party Inspection Support
BV, SGS, Intertek, and other third-party inspection services can be arranged to ensure product compliance with global standards.
Strict Dimensional Control
Tight tolerances on OD, wall thickness, and length ensure high consistency and reliability during installation and fabrication.
Superior Surface Quality
Surface treatment options (black coating, varnish, galvanizing, oiling, or 3PE/FBE) provide enhanced corrosion resistance and extend service life.
Excellent Weldability and Formability
Q195/Q215/Q235/Q345 material grades offer good ductility, easy welding, and convenient cutting or bending during fabrication.
High Strength-to-Weight Ratio
Hollow section design provides strong structural support while keeping the overall weight lower compared to solid steel.
Wide Compatibility for Multiple Applications
Suitable for structural engineering, machinery manufacturing, greenhouse frames, fences, and fluid transportation lines.
Large-Scale Production Capacity
With stable monthly output, bulk orders and fast delivery can be guaranteed for domestic and overseas customers.
