Visual Testing (VT) Practice Exam

Pitting corrosion is primarily categorized as which type of corrosion?

1. Occluded cell corrosion

2. Stress corrosion

3. General corrosion

4. Galvanic corrosion

The correct answer is: Occluded cell corrosion

Pitting corrosion is primarily classified as occluded cell corrosion. This form of corrosion arises from localized breakdowns in the protective oxide layer on metal surfaces, leading to the formation of small pits or holes. These pits can penetrate deeply into the metal, causing significant damage over time. Occluded cell corrosion occurs in areas where oxygen supply is limited, such as under deposits or in crevices. This restriction can lead to differential aeration, creating a situation where an anode and cathode are formed in close proximity, promoting localized corrosion. In contrast to this, stress corrosion and general corrosion distribute more uniformly across a surface, while galvanic corrosion involves the interaction between different metals in an electrolyte. Thus, the characteristics and mechanics of pitting corrosion align closely with those of occluded cell corrosion, making it the correct classification.