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CLEANING & CORROSION CONTROL FINAL
CORE MATERIAL MAINTENANCE AND
CORROSION PREVENTION REVIEW 2026
โ This is an attack resulting from a direct exposure of bare surface to caustic liquid or gaseous agents. Answer: Direct Chemical attack or pure chemical corrosion โ True or False: The changes in direct chemical attacks are occurring simultaneously at the same point Answer: True โ What are the most common agents causing direct chemical attack on aircraft? Answer: - Spilled battery acid or fumes from batteries
- Residual flux resulting from inadequately cleaned, welded, brazed, or soldered joints
- Entrapped caustic cleaning solutions โ With the introduction of these 2 types of batteries, spilled battery acid is becoming less of a problem, the use of these closed units lessens the hazards of acid spillage and battery fumes Answer: Sealed lead-acid & Nickel-cadmium batteries
โ True or false: Flux resides are hygroscopic in nature Answer: True โ Absorb moisture, and unless carefully removed tend to cause severe pitting Answer: Flux residues (hygroscopic) โ True or false: Fluxes used in brazing, soldering, and welding are corrosive, and they chemically attack the metals or alloys with which they are used. Answer: True โ What is important to remove from a metal surface immediately after a joining operation that uses a flux Answer: Remove the residual flux โ True or False: Where entrapment of a cleaning solution is likely to occur, use a noncorrosive cleaning agent, even thought it is less efficient Answer: True
Answer: Nobility โ True or False: The less noble a metal is, the more easily it can be corroded Answer: True โ Metals chosen for use in aircraft structures are studied compromises of what against the structures needs? Answer: Strength, weight, corrosion resistance, workability, and cost โ Exposure of the alloy surface to a conductive, corrosive medium causes the more active metal to be anodic, and the less active metal to become catholic, thereby establishing conditions for corrosion. What are these called? Answer: Local Cells โ This attack is responsible for most forms of corrosion on aircraft structure and component parts Answer: Electrochemical attacks โ True or False: The greater the difference in electrical potential between two metals, the greater will be the severity of corrosive attack, if the proper conditions are allowed to develop Answer: True
โ What are the 7 forms of corrosion discussed in the book? Answer: Surface Corrosion Filiform Corrosion Dissimilar Corrosion Inter-granular Corrosion Stress Corrosion Fretting Corrosion False Brinelling โ Occurs as a result of the combined effect of sustained tensile stresses and a corrosive environment? Answer: Stress Corrosion โ True or false: stress corrosion cracking is found in most metal systems, however is particularly characteristic of aluminum, copper and certain stainless steels and high strength alloy steels with over 240,000 psi Answer: True โ Stress Corrosion may be trans-granular or inter-granular in nature Answer: True
โ Not unlike electroplating, occurs at the points or areas of contact where the insulation between the surfaces has broken down or been omitted Answer: Galvanic action โ This electrochemical attack can be very serious because in many instances the action is taking place out of sight, and the only way to detect it prior to structural failure is by disassembly and inspection Answer: Dissimilar Metal Corrosion โ Contamination of a metal's surface by what means can also induce dissimilar metal corrosion? Answer: Mechanical โ True or False: The improper use of steel cleaning products such as steel wool or a steel wire brush on aluminum or magnesium, can force small pieces of steel into the metal being cleaned, which will then further corrode and ruin the adjoining surface Answer: True โ This type of corrosion is an attack along the grain boundaries of an alloy and commonly results from a lack of uniformity in the alloy structure. Aluminum alloys and some stainless steels are particularly susceptible to this form of electrochemical attack.
Answer: Inter-granular Corrosion โ True or false: Lack of uniformity is caused by changes that occur in the alloy during heating and cooling during the material's manufacturing process Answer: True โ Very severe inter-granular corrosion may sometimes cause the surface of a metal to what? Answer: Exfoliate โ This is a lifting or flaking of the metal at the surface due to de- lamination of the grain boundaries cause by the pressure of corrosion residual product build up Answer: Exfoliation โ Appears as a general roughening, etching, or pitting of the surface of a metal, frequently accompanied by a powdery deposit of corrosion products Answer: Surface Corrosion โ True or False: Surface corrosion may be caused by either direct or electrochemical attack Answer: True
โ What should you consult for information on any chemicals used in preventive maintenance Answer: MSDS โ Corrosion preventive maintenance include the following specific functions Answer: 1 - Adequate cleaning 2 - Thorough periodic lubrication 3 - Detailed inspection for corrosion and failure of protective systems 4 - Prompt treatment of corrosion and touchup of damaged paint areas 5 - Keep drain holes free of obstructions 6 - Daily draining of fuel cell sumps 7 - Daily wipe down of exposed critical areas 8 - Sealing of aircraft against water during foul weather and proper ventilation on warm, sunny days 9 - Maximum use of protective covers on parked aircraft โ Om addition to routine maintenance inspections, amphibians or seaplanes should be check how often? Answer: Daily, and critical areas cleaned & treated
โ Are both jet and reciprocating engine exhaust deposits very corrosive? Answer: Yes, give particular attention where gaps, seams, hinges, and fairings โ What will minimize corrosion of acid deposits? Answer: Regular cleaning and neutralization of acid deposits โ These are natural sumps for waste hydraulic fluids, dirt, and odds and ends of debris. Residual oil quite often masks small quantities of water that settle to the bottom ad set up a hidden chemical cell Answer: Bilge Areas โ Instead of using chemical treatments for the bilge water, current floor manufacturers recommend what? Answer: - Diligent maintenance of the internal coatings
- Interior compartments are painted to protect โ Inspection procedures should include particular attention paid to areas located under what? Answer: Galleys and Lavatories
With special attention to places where WHAT may be built up during marine operations? Answer: Engine Frontal Areas and Cooling Air vents Salt Deposits โ How should flap and spoiler recesses be inspected? Answer: With spoilers and or flaps in the fully deployed position โ Relatively little corrosion trouble is experienced with WHAT, if the original surface finish and insulation are adequately maintained Answer: Magnesium Skins โ Why are piano type hinges prime spots for corrosion? Answer: Due to the dissimilar metal contact between the steel pin and aluminum hinge โ True or false: Any inspection for corrosion should include aluminum skin surfaces with special attention to edges, areas around fasteners, and cracked, chipped or missing paint Answer: False, magnesium skin surfaces โ Piano-type hinges are natural traps for what? Answer: Dirt, salt and moisture
โ What type of lubricants are used when servicing piano hinges? Answer: Water-displacing โ True or false: Inspection of hinges should include lubrication and actuation through several cycles to ensure complete lubricant penetration Answer: True โ Corrosion of metal skins joined by spot welding is the result of what? Answer: Entrance and entrapment of corrosive agents between layers of metal โ What should be done to control cables that have internal corrosion? Answer: Removed โ True or false: Replace light external corrosion Answer: False,remove corrosion with a non-woven abrasive pad lightly soaked in oil or steel wire brush โ In general any complete corrosion treatment involves?
Answer: Nonmetallic โ Ferrous Oxide is generally is a result of? Answer: Rust, generally resulting from atmospheric oxidation of steel surfaces โ It's presence actually promotes additional attack by attracting moisture from the air and acting as a catalyst for additional corrosion Answer: Rust โ What four conditions must exist before electrochemical corrosion can occur? Answer: Anode Cathode Presence of a continuous conductive liquid path (electrolyte) Electrical contact between the anode and cathode โ The most practicable means of controlling the corrosion of steel is the complete removal of corrosion products by what means and restoring what? Answer: Mechanical means Restoring corrosion preventive coating
โ True or False: Mechanical means and restoring corrosion preventive coating are practicable means of control corrosion on HIGHLY STRESSED STEEL Answer: False, use of abrasive papers and compounds, small power buffers and buffing compounds, hand wire brushing, or steel wool are all acceptable cleanup procedures โ True or False: Generally speaking, if at all possible, the steel part should be removed from the airframe for treatment, as it can be nearly impossible to remove all residues Answer: True โ It is essential that that steel surfaces not be what during buffing? Answer: Overheated โ What type of extensive damage may result from a contact between dissimilar metal parts in the presence of a conductor? Answer: Pitting damage โ What form of corrosion may exist without visible surface evidence? Answer: Inter-granular Corrosion
Answer: True โ Treat superficially corroded aluminum areas with what? Answer: 10% solution of chromic and sulfuric acid โ The sequence for treatment of aluminum alloys is? Answer: Remove all grease, dirt, oil Strip Paint Treat with solution of sulfuric and chromic acid Dry treat and restore permanent protective coatings โ What is probably the easiest type of corrosion to detect in its early stages since corrosion products occupy several times the volume of the original metal destroyed Answer: Magnesium โ The beginning of magnesium attack shows as a lifting of the paint films and white spots on the magnesium surface, these rapidly develop into snow like mounds or what is called? Answer: White Whiskers
โ In the treatment of magnesium, allow the chromic acid to remain in place for how long before wiping up the excess with a clean damp cloth Answer: 5 to 20 minutes โ True or False: Magnesium castings, in general are more porous and more prone to penetrating attack than wrought magnesium skins Answer: True โ True or False: All dissimilar joints not involving magnesium are protected by the application of a minimum of two coats of zinc chromate or, preferably, epoxy primer in addition to normal primer requirements Answer: True โ In contact NOT involving magnesium, primer is applied by brush or spray and allowed to air dry for how long between coats Answer: 6 hours โ Corrosion Limits are classified under 4 standard types, what are they Answer: 1) Negligible damage
- Damage repairable by patching
