The initiation of filiform corrosion is associated with

• A. High humidity
• B. Mild surface contamination of solid particles deposited from the atmosphere or residue on the metal surface after processing
• C. Salt spray
• D. High temperature

Answer: (B)

Filiform corrosion starts when there is a small defect or contamination under a coating that disrupts the protective seal. Mild surface contamination—from atmospheric particles or residues left after processing—creates initiation sites by introducing substances that alter the local surface chemistry and roughness. These contaminants can trap moisture and ions under the coating and establish differential electrochemical conditions, forming a tiny anodic area that drives the corrosion to propagate along the interface as thread-like filaments under the coating.

Environmental factors like high humidity, salt spray, or high temperature influence how quickly this initiation and growth occur, but they don’t by themselves create the initiation site. They provide the moisture, electrolytes, or accelerated kinetics that make the filiform fronts spread once initiation has begun.