What is usually the cause of dissimilar metal corrosion?

• A. It is usually the result of faulty design or improper maintenance practices
• B. It is caused by identical metals in seawater
• C. It occurs only at high temperature
• D. It occurs only when coatings are applied

Answer: (A)

Dissimilar metal corrosion, or galvanic corrosion, happens when two different metals are in electrical contact in an electrolyte. The metal that is more anodic corrodes faster while the cathodic metal is spared. In practice, this is most often seen when materials that should be isolated are joined or when joints are not properly insulated or protected, or when coatings fail and expose the metal-to-metal contact to the electrolyte. That’s why saying it’s usually the result of faulty design or improper maintenance makes sense: proper design and upkeep aim to prevent direct contact between incompatible metals and to protect or insulate joints, coatings, and connections. The other ideas don’t fit because galvanic corrosion isn’t limited to identical metals, to high temperatures, or to situations only involving coatings—it occurs whenever dissimilar metals are in contact in an electrolyte, at a range of temperatures, and can be mitigated by proper materials selection, isolation, and protection.