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

Daniel Barlow

In response to the previous comment:

Galvanized steel in a splash zone behaves very differently than galvanized steel in atmospheric conditions. In atmospheric conditions, a passive and protective layer known as the zinc patina is allowed to form. In a splash zone, this layer is not allowed to form as it is continually being dissolved by seawater and then being allowed to partially reform. This leads to zinc corrosion rates five times greater than the zinc which is immersed.

A duplex system will be the best way to combat these highly corrosive environments.  A paint, epoxy, or dielectric coating will act as a barrier protection to the zinc. Trying to use cathodic protection to the zinc (which is already providing cathodic protection to the steel) does not usually have positive results and is not recommended practice.

Mohammed Ali

We would like to use galvanized steel piles in seawater in a coat guard base in Alaska. What kind of life should we expect especially in the splash zone? Would you recommend a dielectric coating on top of the galvanizing? We can also provide galvanic cathodic protection with zinc anodes on galvanized steel piles. Do you see any problem with this or should we provide a coating and then add cathodic protection?

Thank you

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