A galvanized square tube is a hollow steel section with a square cross-section that has been coated with a layer of zinc to protect against corrosion. The base tube is typically manufactured as a welded tube (formed from steel coil and electric resistance welded) and then galvanized, most commonly by the hot-dip galvanizing process. In this process, the square tube is immersed in a bath of molten zinc at approximately 450°C (840°F), forming a metallurgically bonded zinc-iron alloy coating. For less demanding indoor applications, electro-galvanizing (a thinner coating applied by electroplating) is available.

The hot-dip galvanized coating provides excellent corrosion resistance, typically ranging from 45 to 200 micrometres (µm) in thickness (average 80–100 µm), corresponding to a coating mass of approximately 460 to 800 g/m². This gives the tube a long service life of 25 years or more in outdoor or moderately wet environments. Electro-galvanized square tube has a much thinner coating (5–25 µm) and is suitable only for mild, indoor conditions.

Square tubes are widely used in structural and mechanical applications because their flat faces allow easy joining, bolting, welding (with precautions), and surface mounting. They offer high strength-to-weight ratios and good torsional resistance.

Key standards for galvanized square tube include:

● EN 10219 (European) – Cold formed welded structural hollow sections, hot-dip galvanized.

● ASTM A500 (American) – Cold formed welded and seamless carbon steel structural tubing (can be galvanized after fabrication).

● JIS G 3466 (Japanese) – Carbon steel square tubes for general structural purposes, galvanized.

● ASTM A653 / A123 – Coating specifications for galvanized products.

Common applications include:

● Construction: building frameworks, columns, beams, bracing, roof trusses.

● Fencing, gates, handrails, guardrails, and balustrades.

● Agricultural equipment, greenhouse frames, livestock pens.

● Industrial shelving, storage racks, workbenches, and machinery guards.

● Furniture frames (tables, chairs, shelving units).

● Automotive and trailer components.

● Signposts and street furniture.

Connection methods: welding (preferred before galvanizing if possible; if welded after galvanizing, the affected area must be repaired with zinc-rich paint), bolting through pre-drilled holes, or using mechanical fasteners. Threading is not common for square tubes.

Galvanized square tube offers an excellent balance of strength, corrosion resistance, and aesthetic appearance (smooth, shiny surface). For most outdoor structural and fencing applications, hot-dip galvanized square tube is the standard choice. Electro-galvanized square tube is used only for indoor, dry environments where corrosion risk is low and a lower cost is desired.