Corrosivity Zones for Steel Construction from Galvanizers Association

The corrosivity of particular environments, called Corrosivity Zones, have been widely researched and the corrosion rates of both steel and zinc are divided into six general categories.

Table 1 shows the comparative corrosivity rate of mild steel and zinc for the first year of service in various environments. The corrosion rate table uses the internationally recognised standard corrosion rates for mild steel and zinc metal from ISO 9223. Note that the corrosion rate for the first year is typically higher than the measured longterm averages.

The Categories are somewhat arbitrary as their purpose is to provide guidance to designers on expected corrosion zones, hence the significant variation of corrosion rates within each zone.

If a designer needs information that is more accurate then they should seek out specific testing data for the location concerned.