Pitting corrosion forms as localized anodic areas and may be detected by what signs?

Pitting corrosion forms as localized anodic areas and may be detected by what signs?

• A. Uniform dulling
• B. Localized anodic areas with potential through-thickness attack
• C. White powder on surface or small pockmarks
• D. No visible signs

Answer: (D)

Pitting corrosion is a localized anodic attack that creates small, discrete pits rather than a uniform thinning of the metal. It starts where a protective film or passive layer breaks down at a tiny area, often under the influence of chlorides, so the damage remains focused in those spots and can progress deeper while the surrounding surface looks relatively intact. Because the attack is localized, you look for surface indicators rather than a uniform change across the area. In aluminum alloys common to aviation, the corrosion products around the pits can form a white, powdery residue, and the pits themselves appear as small craters or pockmarks. So the signs you’d expect are white powder on the surface or small surface pockmarks. Uniform dulling would point to uniform corrosion, not pitting, and no visible signs would not be typical for pits that have progressed to a detectable level.

Pitting corrosion is a localized anodic attack that creates small, discrete pits rather than a uniform thinning of the metal. It starts where a protective film or passive layer breaks down at a tiny area, often under the influence of chlorides, so the damage remains focused in those spots and can progress deeper while the surrounding surface looks relatively intact. Because the attack is localized, you look for surface indicators rather than a uniform change across the area. In aluminum alloys common to aviation, the corrosion products around the pits can form a white, powdery residue, and the pits themselves appear as small craters or pockmarks. So the signs you’d expect are white powder on the surface or small surface pockmarks. Uniform dulling would point to uniform corrosion, not pitting, and no visible signs would not be typical for pits that have progressed to a detectable level.