What is galvanic corrosion and how can it be mitigated in shipboard assemblies?

• A. Corrosion accelerated by electrical contact between dissimilar metals in an electrolyte; mitigate by coatings, isolation, proper material pairing, and sacrificial anodes
• B. Corrosion caused by air exposure
• C. Erosion due to fluid flow
• D. Wear from vibration

Answer: (A)

Galvanic corrosion happens when two dissimilar metals are in electrical contact in an electrolyte, such as seawater or moisture found on a ship. The difference in electrochemical potential makes current flow from the more active metal (the anode) to the less active metal (the cathode). The anodic metal dissolves faster, while the cathodic metal is spared or only lightly affected. The rate depends on how different the metals are, how conductive the electrolyte is, and the temperature and contact geometry.

In shipboard assemblies, you mitigate it by preventing electrical paths between different metals or by making the path nonconductive. Use metals with closer electrochemical potentials or install protective coatings to keep the electrolyte from reaching the metal surfaces. Isolate joints with nonconductive barriers or gaskets to stop direct electrical contact, and employ sacrificial anodes to protect the more susceptible metal. Regularly inspect coatings and anodes, and replace anodes before they’re spent. When using dissimilar metals, ensure proper bonding and insulation so that a galvanic cell cannot form in the seawater.

Some other forms of corrosion are not galvanic. Air exposure corrosion results from oxygen in the environment, erosion comes from fluid flow removing material, and wear from vibration is mechanical wear. The galvanic form specifically involves electrical coupling of different metals in an electrolyte and is treated with coatings, insulation, material pairing, and sacrificial protection.