What is the primary purpose of insulation between dissimilar metals in a cathodic protection (CP) context?

• A. To improve electrical contact
• B. To prevent galvanic coupling that would accelerate corrosion of the anodic metal
• C. To enhance heat transfer between metals
• D. To reduce paint adhesion

Answer: (B)

Preventing galvanic corrosion is the key idea. When two dissimilar metals touch in an electrolyte, a galvanic cell forms: the more active metal becomes the anode and corrodes faster, while the other metal is protected. In a cathodic protection system, unwanted galvanic coupling between different metals can draw protective current away and accelerate corrosion of the anodic metal, undermining CP effectiveness. Insulation between the metals stops electrical contact, so they cannot form that galvanic couple and the anodic metal won’t be driven to accelerated corrosion. The other options aren’t about stopping electrochemical interaction between dissimilar metals, which is why insulation is used.