Cleaning and Corrosion Control practice questions

Answer: A) White, powdery, snow-like deposits

• ACorrect. Magnesium corrosion products appear as white powdery spots.
• BIncorrect. Red-brown rust is iron oxide on steel.
• CIncorrect. Green deposits are typical of copper alloys.
• DIncorrect. Corrosion dulls the surface.

Answer: D) Moisture, especially salt water

• AIncorrect. Sealant keeps electrolyte out.
• BIncorrect. Dry air is a poor electrolyte.
• CIncorrect. Intact paint separates metal from moisture.
• DCorrect. Moisture completes the circuit between the metals.

Answer: B) A general roughening or etching of the surface

• AIncorrect. Isolated deep cavities describe pitting corrosion.
• BCorrect. Uniform attack spreads evenly over the exposed surface.
• CIncorrect. That describes filiform corrosion.
• DIncorrect. That describes exfoliation corrosion.

Answer: A) They are corrosive and collect in seams, hinges, and fairings downstream of the exhaust

Engine exhaust deposits are very corrosive. They build up in the exhaust trail area, especially in gaps, seams, hinges, and fairings downstream of the exhaust, so they should be cleaned off promptly.

• ACorrect. FAA corrosion guidance identifies exhaust trail areas as corrosion-prone. The deposits are very corrosive and give particular trouble where gaps, seams, hinges, and fairings lie downstream of the exhaust outlets. Trapped deposits can escape normal cleaning.
• BIncorrect. Exhaust residue stays corrosive after it cools. The concern is ongoing attack on the metal, especially where moisture and residue are trapped.
• CIncorrect. Removing the deposits is not just cosmetic. They are corrosive to the skin and its finish.
• DIncorrect. The airflow carries exhaust products aft. The exhaust trail area downstream of the stacks or nozzles is where the deposits collect and cause corrosion.

Answer: B) A sodium bicarbonate (baking soda) solution

Lead-acid batteries use sulfuric acid electrolyte, which is neutralized with a mild base: sodium bicarbonate solution. Boric acid (and other weak acids) is for the alkaline electrolyte of nickel-cadmium batteries.

• AIncorrect. Boric acid is a weak acid used to neutralize the alkaline potassium hydroxide electrolyte of nickel-cadmium batteries. It does not neutralize sulfuric acid.
• BCorrect. FAA corrosion guidance specifies a sodium bicarbonate solution to neutralize sulfuric acid deposits from lead-acid batteries.
• CIncorrect. Acetic acid is an acid. It cannot neutralize sulfuric acid electrolyte; acidic neutralizers are only suitable for alkaline electrolyte.
• DIncorrect. MEK is a solvent for cleaning and paint removal. It does not chemically neutralize acid.

Answer: A) Iron oxide (rust)

• ACorrect. Red rust is iron oxide on steel.
• BIncorrect. That is white or gray.
• CIncorrect. That is greenish.
• DIncorrect. This is corrosion.

Answer: D) Concentration cell (crevice)

• AIncorrect. Exfoliation lifts metal in layers along the grain.
• BIncorrect. Filiform corrosion forms worm-like trails under paint.
• CIncorrect. Fretting results from small relative motion between parts.
• DCorrect. Differences in oxygen or ion concentration drive this corrosion.

Answer: D) Embedded steel particles

• AIncorrect. The problem is contamination.
• BIncorrect. The problem is contamination.
• CIncorrect. The problem is contamination.
• DCorrect. Embedded steel particles cause galvanic corrosion; aluminum wool or approved abrasives are used.

Answer: D) Exfoliation

• AIncorrect. That attacks the surface evenly.
• BIncorrect. Filiform forms under paint.
• CIncorrect. Fretting needs relative motion.
• DCorrect. Exfoliation is a severe intergranular form that delaminates the metal in layers.

Answer: A) To keep moisture out of the joint

• ACorrect. Without an electrolyte, galvanic corrosion cannot proceed.
• BIncorrect. Fasteners still carry the load.
• CIncorrect. Sealant's role is moisture exclusion.
• DIncorrect. Sealant is not used for balance.