Aircraft Corrosion Locations (AVT 2113) PDF

AVT 2113 Common Locations of Corrosion: 1. Engine Exhaust Area- The heat and gases (hydrocarbon fuel) that passes through the exhaust contain of constituents for potent electrolyte, because of the elevated temperature corrosion can form all the more rapidly. - cracks and...

AVT 2113 Common Locations of Corrosion: 1. Engine Exhaust Area- The heat and gases (hydrocarbon fuel) that passes through the exhaust contain of constituents for potent electrolyte, because of the elevated temperature corrosion can form all the more rapidly. - cracks and seams, fairings of the nacelles, hinges and fasteners. - inspection should include removal of fairings and access plates in the exhaust gas path. - gaps, seams, hinges, and fairings are areas where exhaust trail deposits may be trapped and normal cleaning methods cannot reach these areas. 2. Battery Compartments and Vents- These batteries store electrical energy and converts into chemical energy. Those fumes come from an overheated battery electrolyte that is difficult to contain and will spread to the structure. - sulfuric acid - sump jar is prone to corrosion 3. Lavatories and Food Services - Organic materials such as food and human waste are (acidic and) highly corrosive to aluminum surfaces. 4. Wheel Wells and Landing Gears- debris from the runway surface may be thrown up into this area - abrasives/chemicals may remove the protective lubricants and coatings; water and mud can freeze and cause damage from the ice formation. - aircraft wheels and wheel well areas should receive frequent cleaning, lubrication, and paint touch-up. - do not use preservative coatings on landing gear wheels. 5. External Skin Area - External aircraft surfaces are ordinarily covered with protective finishes, and operators can also apply paint coatings. Affected external aircraft surfaces are readily visible. - Seams and Lap Joints – where concentration cell corrosion frequently appears sheared edges expose the alloy without the protection of the aluminum - Engine Inlet Area - one of the most vital parts of an airplane is the area directly in the front of the engine where air is taken in. this area is usually quite large, and air rushes into the engine at a highly velocity. abrasion by this high velocity air contaminant carried in the air will trend to remove any protective coating. 6. Inaccesible Areas: - Fuel tanks - are places where corrosion is highly likely to form. As discussed in the area on organic growths as a cause of corrosion, we saw that turbine fuel can hold microscopic “bugs” in suspension until they have an opportunity to join together and grow into the water. - Magnesium Skins- properly surface-treated, insulated, and painted magnesium skin surfaces give relatively little corrosion-related trouble if the original surface is maintained. However, trimming, drilling, and riveting destroy some of the original surface treatment. - Piano- Type Hinges- prime spots for galvanic corrosion due to dissimilar metal contact between the hard carbon steel pin and aluminum alloy hinge tangs. - Control Surfaces Rcesses- movable surfaces on the wings (rudder, elevator, flaps) - Bilges- bottom of the fuselage and below the floorboards. common troubled area natural sump or collection point for waste hydraulic fluids, water, dirt, loose fasteners, drill chips, and debris. - Landing Gear Boxes- these are few areas in a modern fixed gear airplane that are highly stressed. under the rivet heads and bolts, floor tape markings, tubings - Engine Mount Structure- the current flowing through the joints in an aluminum alloy mount will create potential difference. WELDED steel tube mounts are protected from corrosion by filling each tube with hot linsed oil.  7. Control Cables- cables used are made of carbon steel or corrosion resistant steel. - 1. Release tension, 2. Twist the lay, 3. Inspect between the strands - spray/ Coat cables with waxy greases such as PAR-AL-KETONE 8. Welded Areas- Spot-Welded Skins- corrosion of this type is chiefly the result of the entrance and entrapment of moisture or other corrosive agents between layers of metal - Aluminum welding require the use of flux to exclude oxygen from the weld. This flux may contain lithium chloride, potassium chloride, potassium bisulphide or potassium fluoride. These are extremely corrosive to aluminum; all traces of the flux must be removed after wilding is complicated. Welding flux is soluble in water and may be removed with hot water and non-metallic bristle brush. 9. Electronics Equipment Compartment - These areas are cooled by ram air or compressor bleed air and are subject to the same conditions as engine and accessory cooling vents and engine frontal areas. While the degree of exposure is less because of a lower volume of air passing through the compartment and special design features preventing water formation in enclosed spaces. LUBRICANTS & PROTECTION: 1. Hot- linsed oil- engine mount structure and welded areas 2. Water Displacing Lubricant/ Thin Film Fluid- piano hinges and electronic equipment compartment 3. Par- Al- Ketone- control cables 4. Transparent Plastic Film- circuit board Types of Inspection: 100 hours, Annual, Ultrasonic, X-Ray Prevention - corrosion prevention of aircraft structure depends on a comprehensive corrosion prevention and control plan, implemented from the start of operation of an aircraft. 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.Keeping 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 Cleaning compounds work by dissolving soluble soils, emulsifying oily soils, and suspending solid soils. - Highly alkaline cleaning compounds (pH greater than 10) are not recommended. - Moderately alkaline cleaners (pH between 7.5 and 10) conforming to MIL-C-85570, Types I and II, are recommended. Both types contain detergents, foaming agents, and solvents, and work in the same way as a detergent solution. - High gloss spot cleaner conforming to MIL-C-85570, Type III, is recommended for cleaning exhaust track areas of high gloss paint systems. This material contains solvents, detergents, and suspended abrasive matter to remove soil by wearing away the surface that holds it. Cleaning Procedures: 1. Remove/disconnect all electrical power; 2. Ground aircraft;  3. Aircraft wash personnel should wear protective gear (gloves, goggles, aprons, etc.); 4. Protect against water/cleaning compound intrusion (close doors, openings, cover vents, pitot static openings, cover wheels, etc.); 5. Accomplish prewash lubrication. Lubricate in accordance with applicable maintenance manual; 6. Mix cleaning solution to manufacturer's recommendation; 7. Use spray not a stream of water during aircraft wash: 8. Do not use abrasive cleaning pads; and 9. Rinse aircraft with fresh water to remove all cleaning compounds. The following post- cleaning procedures are recommended: 1. Remove all covers, plugs and masking materials; 2. Inspect and clear all drain holes; 3. Inspect open and all known water trap areas for water accumulation and proper drainage: 4. Lubricate aircraft in accordance with applicable maintenance manual; and 5. Apply operational preservation. Preservation- day to day application of corrosion preventive compounds is used to protect metal aircraft parts and components. Surface Treatment - An important step in the corrosion control process is the surface treatment of the metal with a prescribed chemical to form a protective film. Chemical surface treatments properly applied provide corrosion resistance to the metal and improve the adhesion of subsequently applied paints. These surface treatments, also known as chemical conversion coatings, chromate conversion coatings, chemical films, or pretreatments, are aqueous acid solutions of active inorganic compounds which convert aluminum or magnesium surfaces to a corrosion resistant film. - Aluminum and aluminum alloys chemical conversion materials conform to MIL-C-81706. - Magnesium alloy chemical conversion materials conform to MIL-M-3171. - Ferrous metals, stainless steel, and titanium treatment prior to painting are limited to corrosion removal and cleaning Inspection Requirements- is a continuing requirement and should be accomplished on a daily basis. - Most manufacturers' handbooks of inspection requirements are complete enough to cover all parts of the aircraft or engine - Troubled areas, however, are a different matter, and experience shows that certain combinations of conditions result in corrosion in spite of routine inspection requirements. These trouble areas may - The flight routes and bases of operation will expose some airplanes to more corrosive conditions than others. (mild, moderate, or severe) Frequency of Requirements: 1. Aircraft operating in a severe environment should be inspected every 15 days. 2. Aircraft operating in a moderate environment should be inspected every 45 days. 3. Aircraft operating in a mild environment should be inspected every 90 days. 4. The aircraft should be washed prior to any inspection for corrosion. 5. Checks should be performed by a crew familiar with corrosion problems and the nature of their treatment. 6. Operators of low utilization aircraft should develop a corrosion inspection and repair program based on calendar time rather than flight hours. Recommended Depth of Inspection: 1. Daily and preflight inspection. Check engine compartment gaps, seams, and faying surfaces in the exterior skin. Check all areas which do not require removal of fasteners, panels, etc., such as bilge areas, wheel and wheel well areas, battery compartments, fuel cell and cavity drains, engine frontal areas, including all intake vents, and engine exhaust areas. 2. In-depth inspections. In addition to the more common troubled spots that are readily available for inspection, remove screw attached panels, access plates, and removable skin sections as necessary to thoroughly inspect the internal cavities. Inspection should also include removal of questionable heavy internal preservative coatings, at least on a spot check basis. Inspect the interior of the aircraft in corrosion prone areas such as around lavatories, galleys, under floors, baggage compartments. 3. Corrosion inspections should be accomplished at each annual inspection or other scheduled in- depth inspections in which areas of the aircraft not normally accessible will be available for corrosion inspection. Corrosion Monitoring- is observing and checking the progress Corrosion is the gradual destruction of a material (usually metals) caused by interacting with chemicals, electrochemical reactions, friction, or some other environmental factor. Why is corrosion monitoring important? Safety - Corrosion monitoring is important for any industry that uses assets that can degrade over time, but it’s especially important in industries that work with volatile materials, which could explode if not stored properly. - As equipment ages it can become more and more susceptible to corrosion, and less resistant to harsh conditions such as high pressures and temperatures. Cost Reduction - If an asset like a boiler falls apart prematurely due to corrosion it can be incredibly expensive to replace. - In process-intensive industries such as the Chemicals industry, where work is done in refineries or plants which require the use of large storage containers for potentially volatile substances, corrosion can present huge annual costs in terms of damaged equipment. - Corrosion monitoring can help companies avoid these expenses by contributing to the longevity of equipment and assets. Improve Efficiency- In addition to helping prevent accidents and cut costs, corrosion monitoring can improve the efficiency of industrial operations by: - Extending the life of existing assets and of related operational equipment - Providing insights into the kinds of materials that are less likely to corrode for future asset purchasing - Contributing to the identification of cost-effective methods for remedying corrosion growth and related issues. - Identifying conditions related to corrosion in the operating environment—either that contribute to corrosion or that seem to mitigate corrosion—which can then be used to inform purchasing and maintenance decisions. - Reduces facility shutdown time