Which practice helps prevent galvanic corrosion between carbon steel and aluminum in marine environments?

• A. Use dissimilar metals in direct contact without barrier.
• B. Use non-conductive barriers or compatible coatings between metals.
• C. Use only aluminum and remove carbon steel.
• D. Rely on natural passivation of all surfaces.

Answer: (B)

In marine environments, saltwater acts as an electrolyte, so dissimilar metals in contact form a galvanic couple where the more anodic metal corrodes faster. To stop that current flow and protect both metals, you must electrically isolate them from each other and from the electrolyte. A non-conductive barrier (such as plastic spacers, gaskets, or insulating coatings) between the carbon steel and aluminum keeps them from touching and prevents the conductive path the galvanic reaction needs. Applying compatible coatings on the metal surfaces further prevents moisture and electrolyte from bridging any small gaps, maintaining the isolation.

Choosing to place the metals in direct contact without a barrier creates the galvanic couple and accelerates corrosion. Simply removing carbon steel or using only aluminum isn’t always practical in real projects. Relying on natural passivation isn’t dependable in a salty marine setting, where coatings can be damaged and moisture persists.