The Versatility of Galvanized Hollow Sections
Galvanized Hollow Sections (GHS), including Square (SHS) and Rectangular (RHS) forms, are indispensable in modern construction. By applying a protective zinc coating to carbon steel structural tubing, manufacturers provide a material that combines high torsional rigidity with long-term resistance to atmospheric corrosion. These sections are the backbone of solar mounting structures, greenhouse frames, and industrial mezzanines.
Manufacturing and Standards
GHS are typically manufactured following the ASTM A500 (USA) or EN 10219 (Europe) cold-forming specifications. The galvanizing can be performed in two ways:
Pre-Galvanized: The steel strip is galvanized before being formed into a tube. This results in a smooth, consistent finish but leaves the weld seam requiring a secondary repair spray.
Hot-Dip Galvanized (HDG): The finished tube is dipped into a molten zinc bath. This provides a much thicker coating (up to 100μm) and complete coverage, including the internal surface.
Technical Specifications and Sizes
| Parameter | Standard Capability |
|---|---|
| Outside Dimensions | 20x20mm to 400x400mm |
| Wall Thickness | 1.5mm to 16.0mm |
| Zinc Coating Weight | Pre-Galv: 60-120 g/m² | HDG: 300-600 g/m² |
| Mechanical Grade | A500 Grade B, S235JR, Q235B |
Corrosion Resistance and Service Life
The lifespan of a galvanized hollow section is directly linked to the environment. In a typical rural or suburban environment, an HDG section can last over 50 years without maintenance. In coastal areas (C4/C5 environments), the zinc layer provides a sacrificial anode effect, protecting the underlying steel even if the surface is scratched.
Design and Installation Best Practices
When designing with galvanized sections, engineers must ensure proper drainage. For HDG products, internal venting holes are mandatory to prevent pressure explosions during the dipping process. For assembly, high-strength galvanized bolts (ASTM A325) are recommended to maintain consistent corrosion resistance across the entire structure.
FAQs
Is a galvanized section as strong as a black steel one?
Yes. The galvanizing process is a surface treatment and does not alter the core mechanical properties (yield and tensile strength) of the A500 Grade B steel.
Can I paint over a galvanized hollow section?
Yes, this is known as a "Duplex System." It requires a specialized primer (mordant T-wash or epoxy) to ensure adhesion to the zinc surface.
What is the maximum length available?
Standard lengths are 5.8m or 6.0m for container shipping, but custom lengths up to 12m are common for domestic projects.
Are galvanized sections suitable for welding?
Yes, but the zinc must be ground off near the weld area to prevent weld porosity and dangerous zinc fumes. The weld must then be repaired with zinc-rich paint.
Which is better for solar racks: Pre-Galv or HDG?
For utility-scale solar plants, HDG is preferred for its superior coating thickness and 25+ year corrosion guarantee.
