Galvanized Square Tube: A Complete Guide to Specifications, Standards, and Applications

What Is a Galvanized Square Tube?
A galvanized square tube (also called GI square tube or galvan square tube) is a cold-formed steel hollow section with equal side lengths, coated with zinc to prevent corrosion. These rectangular steel tubes combine structural strength with durability, making them ideal for outdoor and industrial applications.

Material Grades for Galvanized Square Tubes
Galvanized square tubes are manufactured from base steel grades that comply with regional standards:
Common Steel Grades
ASTM A36 (USA): General-purpose carbon steel with 36,000 psi yield strength.
Q235 (China GB/T 3094): Low-carbon steel with excellent weldability.
S235JR (Europe EN 10219): Non-alloy structural steel with 235 MPa minimum yield strength.
JIS G3444 (Japan): Zinc-coated steel tubes for mechanical and structural uses.
Classification of GI Square Tubes
Galvanized steel tubes are categorized by production method and zinc coating type:
1. By Manufacturing Process
Hot-Dip Galvanized (HDG): Immersed in molten zinc (60-100 µm coating).
Electro-Galvanized (EG): Electroplated zinc layer (5-15 µm coating).
2. By Surface Finish
Regular Spangle
Minimal Spangle
Smooth Finish (for painting)

International Standards for Galvanized Square Tubes
Different countries follow specific standards for square steel tube production:

Standard Sizes and Dimensions
GI steel pipe dimensions vary based on application requirements:
Common Sizes (Width × Height × Thickness)
Square Tubes: 20×20×1.2mm to 200×200×6mm
Rectangular Tubes: 25×15×1.2mm to 250×150×8mm
Wall Thickness Options
Light Gauge: 0.8mm – 2.0mm
Heavy Duty: 2.5mm – 6.0mm

Key Applications of Galvanized Square Tubes
Steel pipes with zinc coatings are versatile across industries:
1. Construction
Structural frameworks
Roofing supports
Fencing and handrails
2. Automotive
Chassis components
Trailer manufacturing
3. Agriculture
Greenhouse frames
Irrigation systems
4. Industrial
Conveyor systems
Machine guards

Advantages of Using GI Square Tubes
Corrosion Resistance: Zinc coating offers 20-50 years of rust protection.
Cost-Effective: Lower maintenance than stainless steel.
High Strength-to-Weight Ratio: Ideal for load-bearing structures.
How to Choose the Right Galvanized Steel Tube
Consider these factors:
Environment: HDG for coastal/high-moisture areas.
Load Requirements: Thicker walls for heavy loads.
Compliance: Match standards (e.g., ASTM A500 for US projects).
Maintenance Tips for Longevity
Inspect for scratches exposing bare steel.
Reapply zinc-rich paint if damaged.
Avoid contact with copper or brass to prevent galvanic corrosion.

Galvanized square tubes (GI square tubes) are indispensable in modern engineering due to their durability, adaptability, and compliance with global standards like ASTM, EN, and JIS. Whether you need rectangular steel tubes for architectural designs or steel pipes for industrial machinery, understanding material grades, sizes, and regional specifications ensures optimal performance.