Corrosion of a component, such as a bolt, can vary markedly depending on if it is simply in a marine atmosphere, a splash zone, or submerged in seawater.  Maintenance costs for ships, offshore structures and related equipment are dependent on how marine corrosion issues and failures are managed.

In addition to the salt (NaCl) in seawater there are other commonly occurring constituents, dissolved gases, living organisms, and various other materials found in seawater.  Rivers, temperature, dissolved oxygen, and pollutants are some examples of issues that may affect the corrosion of a given component in seawater.

Marine atmospheres are generally considered to be one of the more aggressive atmospheric corrosion environments.  Some factors that affect corrosion rates in marine atmospheres are listed below:

• Humidity
• Wind
• Temperature
• Airborne contaminants
• Location
• Biological organisms

Alloy selection, metallic coatings, organic coatings, and cathodic protection are commonly used methods for providing proper corrosion protection to various components.  Thermal spray, galvanizing, and for specific circumstances electroplating are metallic coatings used in various marine corrosion applications.Organic coatings have changed in recent times due to environmental requirements.  Organic coatings have various constituents to enhance properties that provide corrosion protection, antifouling, adhesion, good mechanical strength, or other desirable characteristics.

Cathodic protection can be accomplished by either using an impressed current system or by using sacrificial anode system. Magnesium, aluminum and zinc alloys are the most frequently used sacrificial anode systems.