Corrosion protection of structural steel
Choosing paint, hot-dip galvanizing or duplex systems to AS/NZS 2312, and using surface area per tonne to estimate coating quantities.
Corrosion protection is selected from the atmospheric corrosivity category of the site and the required life to first maintenance. AS 4312 maps Australian locations to categories C1 (very low, dry inland) up to C5 (very high, surf beaches and industrial) and CX.
| System | Standard | Notes |
|---|---|---|
| Paint systems | AS/NZS 2312.1 | Systems are coded (e.g. PUR4, IZS2) with expected durability per corrosivity category. Surface preparation (e.g. Sa 2½ blast) is critical. |
| Hot-dip galvanizing | AS/NZS 4680, AS/NZS 2312.2 | Coating thickness depends on steel thickness. Detail vent and drain holes for hollow sections and closed fabrications. |
| In-line galvanized tube | AS/NZS 4792 | Thin zinc coating (e.g. ZB100/100), suited to low-corrosivity, internal and short-life uses. |
| Duplex (galvanizing + paint) | AS/NZS 2312.2 | Longest life in aggressive environments; synergistic effect. |
| Weathering steel | AS/NZS 3678 (WR350) | No coating, but avoid marine, persistently wet and crevice details. |
Estimating quantities
Every section page lists the external surface area per metre (m²/m) and per tonne (m²/t). Multiply m²/m by member length for paint quantities, or use the weight calculator for a whole cutting list. Galvanizers usually price per tonne, and sections with a high m²/t (thin, light sections) cost more to paint per tonne but galvanize economically.