How does filiform corrosion typically appear on an aircraft structure?

How does filiform corrosion typically appear on an aircraft structure?

• A. Pits on the metal surface
• B. Thread like lines of puffiness under the film of polyurethane or other dense finish system components
• C. Uniform rust staining
• D. Cracks in the coating

Answer: (B)

Filiform corrosion is corrosion that grows under a coating along the coating–substrate interface. Moisture gets behind defects in the finish and travels under the film, forming slender filaments that advance ahead of the corrosion front. This produces thread-like lines of puffiness or wormlike trails beneath a polyurethane or other dense finish. That distinctive under-coating pattern is what you’d look for on aircraft structures, rather than pits on the metal surface, uniform rust staining, or cracks in the coating.

Filiform corrosion is corrosion that grows under a coating along the coating–substrate interface. Moisture gets behind defects in the finish and travels under the film, forming slender filaments that advance ahead of the corrosion front. This produces thread-like lines of puffiness or wormlike trails beneath a polyurethane or other dense finish. That distinctive under-coating pattern is what you’d look for on aircraft structures, rather than pits on the metal surface, uniform rust staining, or cracks in the coating.