FAA Aviation Mechanic Airframe (AMA)Airframe InspectionHard
During a teardown inspection, a technician finds localized corrosion trapped between two riveted aluminum skin lap joints where moisture was retained between faying surfaces. The corrosion products have built up enough to cause visible bulging of the skin. Which type of corrosion is this?
- AFretting corrosion
- BGalvanic corrosion
- CPoultice (crevice) corrosion
- DFiliform corrosion
Show answer & explanationAnswer & explanation
Correct answer: C. Poultice (crevice) corrosion
Poultice corrosion, also called crevice corrosion, occurs when moisture and contaminants become trapped in a tight crevice such as a lap joint or under a gasket, creating a localized corrosive cell. The buildup of corrosion products causes bulging or pillowing at the joint.
Why the other options are wrong
- A. Fretting corrosion results from vibration/rubbing between tight-fitting parts, producing reddish debris, not trapped moisture bulging.
- B. Galvanic corrosion requires dissimilar metals in contact with an electrolyte, not simply trapped moisture.
- D. Filiform corrosion appears as thread-like filaments under a coating, not joint bulging.
Poultice (Crevice) Corrosion
Corrosion that occurs when moisture and debris are trapped in a tight crevice, such as a lap joint or under a fitting, forming a localized corrosive cell that can bulge the surrounding structure.
- Occurs in faying surfaces, seams, and under fasteners
- Caused by trapped moisture and contaminants
- Corrosion products expand and can bulge or pillow the skin
- Prevented by proper sealing and drainage
Memory trick: Poultice = like a wet bandage trapped against skin, festering underneath