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Smoking rivet as evidence of fretting

Aviation Mechanic General (AMG) practice question 29 of 36 on Cleaning and Corrosion Control. ACS element AM.I.G.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA black ring found around a rivet on engine cowling or wing skin, commonly called a smoking rivet, is evidence of which form of corrosion?

  1. AFretting corrosion
  2. BFiliform corrosion of the paint film
  3. CExfoliation of the surface grains
Show the answer and explanation

Correct answer: A. Fretting corrosion

  • A — correct The smoking rivet on engine cowling and wing skins is the most common example of fretting corrosion, and it is identified by a black ring around the rivet.
  • B — incorrect Filiform corrosion is recognized by a worm-like trace of corrosion products beneath the paint film, not by a black ring at a fastener.
  • C — incorrect Exfoliation lifts up the surface grains of the metal through expanding corrosion products at grain boundaries, most often on extruded sections.

BACKGROUND

Fretting corrosion occurs when two mating surfaces that are normally at rest with respect to one another are subjected to slight relative motion. It is characterized by pitting of the surfaces and the generation of considerable quantities of finely divided debris, which cannot escape easily and so produces extremely localized abrasion. The presence of water vapor greatly increases this deterioration, and where contact areas are small and sharp the result can resemble brinell markings, giving rise to the name false brinelling. The most common example of fretting corrosion is the smoking rivet found on engine cowling and wing skins, identified by a black ring around the rivet. Unlike most corrosion, this reaction is not driven by an electrolyte, and moisture may in fact inhibit it.

STUDY TIP

Tie each form of corrosion to its one signature visual cue, since exam items usually describe the appearance and ask you to name the mechanism.

KEY POINTS

  • Fretting comes from slight relative motion between mating surfaces normally at rest.
  • A smoking rivet, seen as a black ring around the rivet, is the classic example.
  • Fretting is not driven by an electrolyte, and moisture may inhibit the reaction.

SOURCES

  • FAA-H-8083-30B ch08 "Fretting Corrosion"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
MORE ON CLEANING AND CORROSION CONTROL

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.