Dissimilar metal corrosion is usually due to which combination of factors?

• A. Faulty design or improper maintenance practices
• B. Equal metals in contact
• C. Coatings preventing contact
• D. Absence of seawater exposure

Answer: (A)

Dissimilar metal corrosion happens when two metals with different electrochemical potentials are touched by each other and wetted by an electrolyte, forming a galvanic cell. The metal that acts as the anode corrodes faster, while the cathode metal is relatively protected. The key is that both a conductive metal pair and an electrolyte are present.

Faulty design or improper maintenance is the best answer because such shortcomings create or fail to prevent those conditions: dissimilar metals coming into contact or being exposed to a conductive environment (like seawater), insufficient insulation, damaged coatings, or improper fasteners. When design or maintenance leaves metals unisolated or inadequately protected, the galvanic couple forms and corrosion accelerates.

If the metals were the same, or if coatings effectively prevented contact, or if there were no electrolyte exposure (no seawater), dissimilar-metal corrosion would be unlikely.