In a mixed-metal assembly exposed to seawater spray, which approach is least effective for preventing galvanic corrosion?

• A. Isolating dissimilar metals with non-conductive barriers.
• B. Applying compatible coatings on metal interfaces.
• C. Selecting metals with similar electrochemical potentials.
• D. Relying on direct contact between dissimilar metals without isolation.

Answer: (D)

When dissimilar metals are in electrical contact in the presence of an electrolyte, such as seawater spray, a galvanic cell forms. The metal with the more negative electrochemical potential acts as the anode and corrodes, while the more noble metal acts as the cathode and is protected. To prevent galvanic corrosion in a mixed-metal assembly exposed to seawater, you use non-conductive barriers to isolate metals, apply compatible coatings to limit electrolyte access and slow electrochemical reactions at interfaces, and choose metals with similar electrochemical potentials to reduce the driving force for current flow.

Relying on direct contact between dissimilar metals without isolation is least effective because it creates an immediate galvanic couple in the electrolyte. The electrical path is unbroken, the potential difference drives substantial current, and the anodic metal experiences accelerated corrosion. In a marine environment with spray, this leads to rapid deterioration of the more anodic metal, undermining the assembly's integrity.