How does galvanized steel perform in seawater splash zones?
Splash zones are the most aggressive environment for hot-dip galvanized steel (or any other protective coating) because as the zinc coating reacts with the chlorides when wetted, zinc corrosion products are formed. Then those corrosion products dry and are later washed away when the steel is wetted again at which time more zinc corrosion products form. That process repeats itself until the galvanized coating is consumed.
An epoxy or paint designed for splash zones would be a good option for applying over the hot-dip galvanized coating in these areas. The paint or epoxy would act as a barrier to protect the galvanized coating, and then when the paint or epoxy is breached, the galvanized coating would provide corrosion protection until consumed. The Duplex Systems publication discusses painting or epoxy coating hot-dip galvanized steel.
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Comments
Neil Bowie
How long will 2mm galvanised steel take to corrode, when infrequently in contact with saline water, please? Many thanks Neil
(AGA)
Hello Neil, Infrequent contact may be acceptable and more regular immersion will be aggressive. Chloride is the most aggressive ion to zinc, especially if present in amounts exceeding 50ppm. This effect is greater in soft waters with low carbonate levels and/or waters where protective scales are unable to form and provide a passive barrier to slow the corrosion rate. A chloride content of 80ppm in soft water causes quite severe corrosion while little-to-no corrosion may occur in hard water with a chloride content of 700ppm.