HDG Hot-Dipped Galvanized High Temperature Exposure

There are some concerns with using hot-dip galvanized steel in an elevated temperature environment. The industry has recommended the service temperature for conventional coatings to be less than 390ºF (200ºC) for long-term exposure. The problems that arise from long-term use at temperatures above 390ºF (200ºC) include peeling, some changes in mechanical properties, and obvious reduction in corrosion protection.

In an air environment, conventional galvanized coatings may withstand long-term continuous exposure of up to several months at 390ºF (200ºC) without separation of the outer zinc layer. The incidence of such failure will depend on the micro-structural characteristics of the coating. Higher temperatures progressively accelerate the separation process to the point where it requires only a few hours at 570ºF (300ºC) to cause peeling.

As discussed, peeling does occur at temperatures above 390ºF (200ºC) and is dependent on the rise in temperature and the duration exposed. But this does not mean that there isn’t any corrosion protection. During peeling, only the outer free zinc layer has become detached, leaving the zinc-iron alloy layers to provide corrosion protection to the steel.