Protective Coatings
Protective coatings isolate metal from the electrolyte and are the primary defense against external and internal corrosion. A candidate should understand surface preparation, coating selection, application variables, and inspection. Surface preparation is usually the single largest factor in coating performance; abrasive blast cleaning to a specified cleanliness and anchor profile governs adhesion. SSPC/NACE surface preparation standards (for example, near-white blast) and profile requirements are frequent test topics.
Traps abound. One is assuming a thicker coating is always better; excessive thickness can cause cracking, solvent entrapment, or poor cure. Another is confusing surface cleanliness with profile: cleanliness removes contaminants, while profile provides mechanical keying, and both are required. Questions may test the difference between dry film thickness (DFT) and wet film thickness (WFT), where WFT = DFT / volume solids fraction. Holiday detection, adhesion testing, and cure checks are also fair game.
Rule of thumb
For a coating with 60% volume solids applied to reach 300 micrometers DFT, the required WFT is 300 / 0.60 = 500 micrometers. Recognizing this relationship quickly resolves many application questions.
Cathodic disbondment matters for buried or immersed coated structures under CP; coatings must resist disbonding where CP current generates alkalinity at coating defects. Also understand that coatings and CP are complementary: coatings reduce current demand, and CP protects defects the coating cannot cover. Environmental conditions during application (humidity, dew point, substrate temperature) drive premature failures, and questions often hinge on whether conditions were within the coating's specified window.