Black square tubing is a rectangular-section tube made of carbon steel, also known as black rectangular tube, black annealed tube, or black skin tube. It can be used as a base material for galvanized or powder-coated square tubes. It has a natural, uncoated surface and can be used directly, providing basic rust resistance. The black surface is an oxide film. It is a mainstream tube used in construction and mechanical structures, primarily characterized by its economy and high strength.
Glory Steel is a manufacturer and supplier of black square tubing in China. We offer cutting, beveling, threading, galvanizing, coating services, and custom sizes.
Specification
| Item | Black steel square tube |
| Alisas | SHS Black Hollow Section |
| MOQ | 10 Tons |
| Material | Q235B, Q355B, Q355C/D, 20#, 45# |
| Wall thickness | 1.0mm – 20mm |
| Length | Customized |
| Side length | 10x10mm – 600x600mm |
| Package | Standard export packaging |
| Delivery time | 10-18 Days |
Features
- Excellent mechanical properties: High tensile strength, high yield strength, and a cross-sectional shape that enhances bending and torsional resistance.
- Outstanding cost-effectiveness: Mature technology, controllable costs, low raw material procurement costs, and we provide anti-corrosion processing services.
- Convenient processing: No need to worry about coating peeling during processing; easy to weld and pierce; precise dimensions; and fits perfectly with bolts.
- Black appearance: The unique black oxide film bonds tightly to the steel substrate and facilitates subsequent spraying or hot-dip galvanizing.
Application
- Building Structures: Primarily used for framing, such as the frame tubes for extended-wing houses and steel platform frames for logistics transfer warehouses.
- Fence Maintenance: Protective railing posts or welded crossbars for railways, highways, fields, and balconies.
- Furniture and Agriculture: Internal base material frameworks for seating and benches; cultivation supports for greenhouses and sunrooms; irrigation supports.
- Machinery and Municipal Engineering: Machinery frames in mining, oilfield drilling, and metallurgical fields; conveyor belt supports; road signs; gas filling station pillars.
Classification by process
- Hot-rolled black square tube: The cheapest option, suitable for mass production. It is made by gradually welding hot-rolled steel strips at high temperatures, resulting in thick walls and strong load-bearing capacity.
- Cold-drawn black square tube: Further precision-processed from hot-rolled black tube, resulting in a high surface finish and accurate dimensions.
- Annealed black square tube: Also called welded black square tube, it is the most widely used type. Compared to hot-rolled black square metal tubing, it undergoes an additional annealing process to eliminate internal stress.
- Seamless black square tube: Requires no welding; it is made through perforation. It has good pressure resistance and fatigue resistance, but is relatively expensive.
Commonly used materials
- Q195: Carbon content less than 20%, relatively easy to cut and pierce, and easy to bend.
- Q235B: Also a carbon structural steel, with moderate strength, it is the most commonly used grade.
- Q355B/Q355C/D: Low-alloy high-strength structural steel, with higher strength than Q235, used for heavy structures.
- 20# / 45#: High-quality carbon steel, used in precision machinery. 20# has good toughness, while 45# has higher strength.
- ST37: German standard structural steel, approximately equivalent to Q235B, also a general-purpose structural steel.
- ST52: German standard structural steel, approximately equivalent to Q355B, high strength, good structural stability.
Material mechanical properties
| Material | Tensile strength (MPa) | Yield strength (MPa) | Elongation (%) | Hardness |
| Q195 | 315~390 | ≥195 | ≥33 | — |
| Q235B | 370~500 | ≥235 | ≥26 | — |
| Q355B | 470~630 | ≥355 | ≥22 | — |
| Q355C/D | 470~630 | ≥355 | ≥22 | — |
| 20# | ≥410 | ≥245 | ≥25 | ≤156HB |
| 45# | ≥600 | ≥355 | ≥16 | ≤229HB |
| ST37 | 360~510 | ≥235 | ≥25 | — |
| ST52 | 490~630 | ≥355 | ≥22 | — |
Black Square Tubing Size & Unit Weight
| Side Length (mm) | Approx. Side Length (inch) | WT (mm) | Approx. WT (inch) | Weight (kg/m) | Weight (lb/ft) |
|---|---|---|---|---|---|
| 25×25 | 1″ × 1″ | 1.5 / 2.0 | 0.059″ / 0.079″ | 1.10 / 1.44 | 0.74 / 0.97 |
| 30×30 | 1-3/16″ × 1-3/16″ | 1.5 / 2.0 / 2.5 | 0.059″ / 0.079″ / 0.098″ | 1.33 / 1.75 / 2.16 | 0.89 / 1.18 / 1.45 |
| 40×40 | 1-9/16″ × 1-9/16″ | 1.5 / 2.0 / 2.5 / 3.0 | 0.059″ / 0.079″ / 0.098″ / 0.118″ | 1.80 / 2.37 / 2.93 / 3.48 | 1.21 / 1.59 / 1.97 / 2.34 |
| 50×50 | 2″ × 2″ | 2.0 / 2.5 / 3.0 | 0.079″ / 0.098″ / 0.118″ | 2.99 / 3.70 / 4.40 | 2.01 / 2.49 / 2.96 |
| 60×60 | 2-3/8″ × 2-3/8″ | 2.5 / 3.0 / 4.0 | 0.098″ / 0.118″ / 0.157″ | 4.48 / 5.33 / 6.98 | 3.01 / 3.58 / 4.69 |
| 80×80 | 3-1/8″ × 3-1/8″ | 3.0 / 4.0 / 5.0 | 0.118″ / 0.157″ / 0.197″ | 7.18 / 9.43 / 11.60 | 4.82 / 6.34 / 7.80 |
| 100×100 | 4″ × 4″ | 3.0 / 4.0 / 5.0 | 0.118″ / 0.157″ / 0.197″ | 9.04 / 11.89 / 14.66 | 6.07 / 7.98 / 9.84 |
Max Unsupported Height & Load Capacity
| Side Length (mm) | Wall Thickness (mm) | Max Unsupported Height (m) | Max Unsupported Height (ft) | Load Range (kg) |
|---|---|---|---|---|
| 25×25 | 1.5 / 2.0 | ≤2.5 / ≤3.0 | ≤8.2 / ≤9.8 | 650 ~ 990 |
| 30×30 | 1.5 / 2.0 / 2.5 | ≤2.8 / ≤3.2 / ≤3.8 | ≤9.2 / ≤10.5 / ≤12.5 | 1,050 ~ 1,950 |
| 40×40 | 1.5 / 2.0 / 2.5 / 3.0 | ≤3.0 / ≤3.5 / ≤4.0 / ≤4.5 | ≤9.8 / ≤11.5 / ≤13.1 / ≤14.8 | 1,580 ~ 3,450 |
| 50×50 | 2.0 / 2.5 / 3.0 | ≤3.8 / ≤4.2 / ≤4.8 | ≤12.5 / ≤13.8 / ≤15.7 | 2,750 ~ 4,750 |
| 60×60 | 2.5 / 3.0 / 4.0 | ≤4.5 / ≤5.0 / ≤5.8 | ≤14.8 / ≤16.4 / ≤19.0 | 4,900 ~ 8,600 |
| 80×80 | 3.0 / 4.0 / 5.0 | ≤5.5 / ≤6.5 / ≤7.5 | ≤18.0 / ≤21.3 / ≤24.6 | 9,500 ~ 16,800 |
| 100×100 | 3.0 / 4.0 / 5.0 | ≤6.0 / ≤7.0 / ≤8.0 | ≤19.7 / ≤23.0 / ≤26.2 | 13,500 ~ 25,000 |
Notes:
- The bearing capacity is a reference value under vertical axial compression, material Q235B, with a safety factor of 4.
- The bearing capacity can be increased by approximately 40% when using Q355B/ST52.
- The above data are for static ideal working conditions. Please verify separately for formal projects.
Formula for calculating weight per meter
Weight per meter (kg/m) = [2 × (A + B) – 4t] × t × 7.85 / 1000.
Where A/B is the side length in mm, t is the wall thickness in mm, and 7.85 is the general density coefficient of steel. The calculated value is the theoretical weight per meter of pipe.
FAQs
1. How many tons can a container hold?
A 20-foot container holds approximately 20-22 tons, and a 40-foot container holds approximately 25-28 tons (depending on size).
2. What standards does the material correspond to?
Q235B ≈ ST37 (German Standard) / ASTM A500 Gr.B (American Standard); Q355B ≈ ST52 (German Standard) / ASTM A500 Gr.C (American Standard).
3. Can it be galvanized/painted?
Yes, black iron square tube is the base material for galvanized square tubing and powder-coated square tubing. We provide hot-dip galvanizing and powder coating services. In addition, we also offer end-treatment services.
Glory Steel factory, located in Tianjin, China, is an ISO 9001, ISO 14001, and CE-certified factory with an annual output of 100,000 tons. We specialize in producing Q235 black tubing, including round, square, rectangular, and oval tubes, as well as zinc-coated, zinc-aluminum-magnesium-coated, and powder-coated corrosion-resistant tubing. With our high-quality products and services, we export to over 120 countries.
