In this important industry, a correct valuation is essential for the prevention or elimination of corrosion. Let's know some recommendations.
by Juan Manuel Álvarez*
In the aeronautical industry, from the point of view of maintenance, the inspections related to the detection of Corrosion that must be made to the structures of aircraft and their components are defined.
Inspections are determined on checklists and classified as periodic and non-periodic, and specified by aircraft area or component.
Once the presence of corrosion is detected, a report is generated that after being evaluated must be considered as repairable or not, according to the condition and measurement that is made. In this way you can keep a log that allows quantifying, by area or component, the repairability by remaining material.
In principle, inspections are based on detection by visual inspection, then by detailed visual inspection and finally by specialized inspection, among which are inspections by Eddy currents, ultrasound inspection, radiographic inspection and other inspection techniques recommended by the aircraft manufacturer depending on the material to be inspected and the accesses.
The causes for which Corrosion can occur in aircraft are mainly based on reactivity with the environment, in which moisture is present that gives rise to the formation of Corrosion products that comply with electrochemical systems. Due to the humidity present in the heights around the aircraft and due to work such as washing aircraft where it is possible that the corrosion control mechanisms are affected, defective or not correctly applied, this will lead to the formation of corrosion, which will be easily detected when coatings and other products for corrosion control are removed in major maintenance services.
Fault Origins
Obviously, the causes of the formation of corrosion products are a consequence of the defects of the protection systems, either by the application or by the non-repair or restitution of the same once it is detected in the periodic inspections. Examples of the sources of failures of protection systems are the following:
The generation of coating defectology due to the impact and / or abrasion by particles that may occur during the reeling of the aircraft from or to the runway to the parking place, as well as during takeoff or landing. Similarly during the flight, the impact or abrasion by particles can occur according to the pollution present in the environment or in the transit zone.
Another source of affectation of coating systems is the runoff of lubricating oils such as skydrol, a fairly acidic and corrosive product used in hydraulic systems. Aviation fuel runoff affects by aging the coatings that protect surfaces such as planes, these runoffs can be originated at the time of the tank that can be by pressure or gravity.
Ultraviolet radiation ages both coatings and other products used for corrosion control such as sealants, which crystallize over time and must be changed to fulfill their purpose.
The delaminations of the coatings caused by the abrasion of the air on the leading edges of the planes are recurrent and generate corrosion products due to the affectation of the protection.
The affectation of lubrication in trains and hinges generates corrosion problems in these components, which will be on the periodic low-frequency checklists.
Inside the aircraft, the presence of corrosion products generated by drips or runoff of different cleaning liquids, passenger consumption, products present in the cargo or luggage is recurrent.
When the aircraft crosses an area where it occurs or has presented volcanic eruption, it will cause Corrosion both in the materials of the turbines or engines, as well as in the structure and components in areas exposed by the defectology of the protection systems. Similarly, corrosion will occur in turbines or engines when an aircraft enters or flies over coastal or maritime areas, which is why turbines or engines must be cleaned at the end of the day.
Coatings and equipment
The coating system used in aircraft recommended by aircraft manufacturers through maintenance manuals is epoxy - polyurethane type, usually bilayer.
The paints used are liquid, usually applied by spraying methods in maintenance procedures and by electrostatic method at the end of the manufacture of the aircraft.
The application equipment of aeronautical paints for the spraying method recommended by aircraft manufacturers through maintenance manuals and standard practices, are HVLP and airless equipment.
The recommended inspections of coatings are destructive and non-destructive in nature. The most common non-destructive inspection is the determination of the dry film thickness, due to the importance in the protection and interference that the coating presents in the weight and balance of the aircraft. Weight and balance that must also be met in aircraft components, mainly in engine propellers and helicopter blades where the imbalance can generate vibrations in flight, for example.
The best prevention tips will be:
- The correct application of corrosion control products in compliance with technical procedures.
- Compliance with periodic inspections.
- Full inspection of checklists.
- Condition monitoring of applied corrosion control products.
- The correct cleaning service of the aircraft in quality and frequency.
- Compliance with scheduled maintenance services for corrosion control.
- The training of all personnel in charge and related to corrosion control.
For compliance with corrosion control in aircraft there is the CPCP, a program for the control and prevention of corrosion, as well as the AP, Aging Program, intended for the assessment of the state of the structures and their components as well as the estimation of the remaining useful life of the materials that make it up.
As always I wish you a good aging and many successes in your work.
* Juan Manuel Álvarez Rodríguez. Designer for Corrosion Control, Certified Coating Inspector, Corrosion Technician and Marine Coating Inspector (NACE International, the Corrosion Society). A.S.T.M. member of the committees of corrosion, paints and coatings, fuels, general aviation, adhesives, nondestructive testing and composites. Certified Instructor ICAO (International Civil Aviation Organization ). Inspector in Non-Destructive Testing. Instructor, lecturer and columnist in Paintings and Corrosion. Specialist in Metal Structures and Composite Materials. Website: Juancorrosion.com Mail: [email protected] - Advisory Services, Inspections, Training and Contracts for the Control and Prevention of Corrosion.
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