In Moisture-Rich Environments
A less common environment for steel in the transportation sector is submerged in or exposed to water. Moisture is highly corrosive to most metals including steel and zinc. However, because of the development of the passive, mostly non-water soluble zinc patina, the corrosion rate of galvanized steel is much slower than bare steel. There are many different types of water (pure water, natural fresh water, potable water (treated drinking water), and seawater) and each has different mechanisms that determine the corrosion rate.
Similar to soils, the varieties of water make predicting corrosion rates difficult. Though pH level has the most profound effect, many parameters affect corrosion of metals in a water environment including oxygen content, water temperature, agitation, the presence of inhibitors, and tide conditions. Despite the difficulty of predicting corrosion, hot-dip galvanizing steel is one of the best methods of corrosion protection for submersed applications because of its complete, uniform coverage.
Bridges host the primary concern for steel in moisture-rich environments, as they often either span water or have submerged substructure elements. For elements completely submerged in water, there is constant exposure to the corrosive attacks of moisture. Galvanized steel performs very well under these conditions, performing flawlessly even in harsh water environments such as seawater for 8 12 years.