Preventing Corrosion of Aircraft Parts

DALLAS — Corrosion of aircraft parts is a significant concern for the industry, as it can lead to reduced efficiency, increased maintenance costs, and even safety hazards.

Aircraft parts are complex systems of metal components, which when exposed to various environmental factors during flight can cause corrosion, which can weaken or damage aircraft parts and systems.

In the aviation industry, corrosion can pose a significant risk to the safety, reliability, and efficiency of aircraft. It is essential to prevent and control corrosion for ensuring the safety and reliability of aircraft.

In 2021, Qatar Airlines (QR) filed a lawsuit with the manufacturer over surface paint issues on the Airbus A350 with a complaint that it had detected cracks in the paint of some of its newly acquired A350 aircraft and subsequently grounded part of its fleet. However, QR and Airbus have already settled the long-standing A350 dispute recently.

Before taking into account the techniques and methods to prevent and control corrosion in aircraft, here are some of the types of corrosion that can occur in aircraft, along with some of the parts where they typically occur.

Surface Corrosion

Surface corrosion is a general term that refers to any type of corrosion that occurs on the surface of a metal component. This type of corrosion may occur in any area of the aircraft that is exposed to a corrosive environment, such as the exterior of the aircraft, fuel tanks, hydraulic lines, and engine components.

Surface corrosion can take on different forms, including uniform corrosion, pitting corrosion, and intergranular corrosion.

Uniform Corrosion

Uniform corrosion is one of the most common types of corrosion in aircraft and can occur on any metal surface exposed to a corrosive environment. Such corrosion usually occurs when a metal surface is exposed to saltwater, acid rain, or high humidity.

Uniform corrosion eventually results in a loss of material thickness and potentially compromises the structural integrity of the affected aircraft part. While uniform corrosion is a type of surface corrosion, not all surface corrosion is uniform.

Some of the common aircraft parts where uniform corrosion may occur include the exterior parts of the aircraft, such as the fuselage, wings, and tail, as well as internal parts such as fuel tanks, hydraulic lines, and engine components.

Pitting Corrosion

Pitting corrosion is a localized form of corrosion that can occur on any metal surface or area where uniform corrosion has been removed. It is characterized by small pits or holes in the metal surface, which can compromise the structural integrity of the part.

Some of the common parts where pitting corrosion may occur include fasteners, landing gear components, and other structural members that are exposed to harsh environmental conditions.

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Intergranular Corrosion

Intergranular corrosion usually occurs along the grain boundaries of a metal, typically in areas where the metal has been sensitized due to exposure to high temperatures, such as during welding or heat treatment.

This type of corrosion may occur in any metal component that has been welded, including fuel tanks, engine components, and other structural members.

Galvanic Corrosion

Galvanic corrosion can occur when two dissimilar metals are in contact with each other in the presence of an electrolyte, such as saltwater or moisture. One metal acts as an anode and corrodes faster than the other metal, which acts as a cathode.

This type of corrosion can occur in any area where dissimilar metals are in contact, including fasteners, electrical components, and structural members.

Dissimilar Metal Corrosion

Dissimilar metal corrosion occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte. This type of corrosion may occur in any area where dissimilar metals are in contact, including fasteners, electrical components, and structural members.

The severity of dissimilar metal corrosion can be influenced by factors such as the size of the anode and cathode, the types of metals involved, and the nature of the electrolyte.

Fretting Corrosion

Fretting corrosion can occur in any area of the aircraft where two surfaces are in contact and undergo repeated small movements. The repeated movement can remove protective coatings and expose the metal to a corrosive environment, leading to corrosion.

Common areas where fretting corrosion may occur include bolted connections, bearings, and other moving parts such as control surfaces. This type of corrosion can be prevented by using lubricants or applying a protective coating.

Stress Corrosion Cracking

Stress corrosion cracking is a type of corrosion that occurs in materials under tensile stress in the presence of a corrosive environment. It is characterized by small cracks that can propagate and eventually cause the part to fail.

Stress corrosion can occur in any part of the aircraft that is under significant stress, such as landing gear components, engine mounts, and structural members. This type of corrosion can be prevented by reducing the tensile stress on the part, using materials that are less susceptible to cracking, or by using a protective coating.

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Techniques to Prevent Corrosion

In order to prevent and treat corrosion in aircraft, it is important to regularly inspect all parts of the aircraft for signs of corrosion and to use appropriate corrosion prevention and control measures.

Generally, aircraft manufacturers and operators apply a variety of methods including a selection of appropriate materials, surface treatments, regular maintenance, environmental control, corrosion inhibitors, monitoring, non-destructive testing, cathodic protection, proper design, and engineering.

By identifying and treating corrosion early, it is possible to prevent damage to aircraft parts and ensure safe, reliable, and efficient operation. Here are some of the widely used techniques and methods to prevent the corrosion of aircraft parts.

Materials Selection, Surface Treatments

Choosing the right materials for aircraft parts and applying appropriate surface treatments is essential for preventing and controlling corrosion. Materials such as aluminum, titanium, and stainless steel are widely used in aircraft manufacturing due to their corrosion-resistant properties. Aluminum alloys are particularly popular in the aviation industry due to their high strength-to-weight ratio, low cost, lightweight and good resistance to corrosion, making them an ideal material for aircraft structures.

Titanium is another popular material used in aircraft manufacturing, particularly in areas that require high strength and corrosion resistance, such as landing gear and engine components. Stainless steel is also commonly used in aircraft manufacturing due to its high corrosion resistance and strength. It is often used for aircraft components that require high strength and durability.

In addition to selecting the right materials, manufacturers and operators use surface treatments for aircraft components and systems to protect them from corrosion. Surface treatments, such as anodizing, chroming, and painting, can help to protect the metal surface from corrosion by creating a barrier against moisture and other corrosive agents.

Anodizing involves applying an oxide layer to the surface of the metal using an electrolytic process, which can provide excellent corrosion resistance. Chromating involves treating the metal surface with chromate, which can create a protective layer against corrosion. Chromatin provides excellent corrosion resistance and adhesion properties. Painting involves applying a layer of paint to the metal surface, which can protect the metal from moisture and other environmental factors.

Regular Maintenance

Regular maintenance of aircraft parts is another critical aspect of preventing and detecting corrosion in aircraft. Maintenance tasks, such as cleaning, inspections, and repairs, can help to detect and prevent corrosion before it causes significant damage. Regular cleaning can help to remove contaminants that can contribute to corrosion, such as dirt, salt, and other chemicals.

Corrosion can occur in hard-to-reach areas such as under panels, inside fuel tanks, or on the underside of the aircraft. Therefore, inspections should be carried out regularly to detect corrosion in these areas. Inspections can help to detect corrosion by identifying areas of rust, discoloration, or pitting on the metal surface. Repairs can help to remove or replace corroded components and systems, which can help to prevent further damage.

Environmental Control

Environmental factors, such as humidity, temperature, and exposure to saltwater, can contribute to corrosion in aircraft. Controlling these factors can help to prevent and control corrosion. Moreover, using corrosion inhibitors, such as desiccants, can help to absorb moisture and protect aircraft parts and systems.

Additionally, proper storage and handling of aircraft parts and systems can help to prevent corrosion by minimizing exposure to environmental factors. For example, storing aircraft in a dry, temperature-controlled environment can help to prevent moisture buildup and minimize the risk of corrosion.

Moreover, aircraft components that are exposed to the elements should be covered to protect them from rain, snow, and other environmental factors. Proper handling of aircraft parts and systems during transport and installation can also help to prevent damage and corrosion.

In coastal areas, saltwater exposure can accelerate the corrosion process. Therefore, aircraft that operate in these areas should be washed regularly to remove salt deposits from the surface. When washing aircraft, it is important to use non-corrosive cleaning agents and avoid using high-pressure water, which can damage the surface of the metal.

Corrosion Inhibitors

Corrosion inhibitors are chemicals that are used to protect aircraft parts and systems from corrosion. These chemicals work by forming a protective layer on the metal surface, which can prevent moisture and other corrosive agents from reaching the metal. Corrosion inhibitors can be applied as coatings, sprays, or in the form of additives to fuels or lubricants.

Coatings are applied as a thin layer on the metal surface and can provide long-lasting protection against corrosion. Common coating materials include epoxy, polyurethane, and silicone. These coatings can be applied using various methods, such as spraying, brushing, or dipping, depending on the size and shape of the component. Coatings can also be customized to meet specific corrosion resistance requirements, such as resistance to saltwater or acidic environments.

Sprays are another form of corrosion inhibitor that can be applied to aircraft parts and systems. Sprays are typically used for hard-to-reach areas or areas that are difficult to coat with traditional methods. Sprays can be applied as a thin layer or as a thicker, gel-like substance that adheres to the metal surface. These sprays can provide temporary protection against corrosion and can be reapplied as needed.

One of the most common types of corrosion inhibitors used in the aviation industry is MIL-PRF-16173, which is a petroleum-based rust-preventive compound. This inhibitor can be applied as a spray or dip, and it provides long-lasting protection against corrosion.

Another type of corrosion inhibitor is the vapor-phase inhibitor (VPI), which is a chemical that is released into the air and can provide protection against corrosion for a wide range of metal components. VPIs work by creating a vapor that condenses onto the metal surface, forming a protective layer that can prevent moisture and other corrosive agents from reaching the metal. The vapor-phase inhibitors can be used for the long-term storage of aircraft parts and components.

Furthermore, additives are another form of corrosion inhibitor that is added to fuels or lubricants. These additives can provide protection against corrosion in critical areas such as engines and fuel systems. For example, some additives can prevent the formation of deposits that can contribute to corrosion or can neutralize acids that can corrode metal surfaces.

Monitoring & Non-Destructive Testing

Monitoring the condition of aircraft parts and systems is crucial for detecting corrosion and preventing further damage. Non-destructive testing (NDT) is a method used to detect corrosion and other defects in aircraft components without damaging or altering the components. Various techniques including visual inspections, ultrasonic testing, X-ray and radiography, eddy current testing, and magnetic particle inspection can be used for monitoring corrosion.

Visual inspections involve a thorough examination of the metal surface for signs of corrosion, such as rust, pitting, or discoloration. Ultrasonic testing involves using high-frequency sound waves to detect changes in the thickness or density of the metal, which can indicate corrosion.

Eddy current testing is a technique that uses electromagnetic induction to detect flaws in the metal surface, and magnetic particle inspection involves applying a magnetic field to the metal surface and using a magnetic powder to detect defects. Radiographic testing involves using X-rays or gamma rays to detect changes in the density or structure of the metal, which can indicate corrosion.

The non-destructive testing technique is an important tool for detecting corrosion in aircraft components, as it can help to identify and address corrosion before it causes significant damage.

Cathodic Protection

Cathodic protection is another technique used to prevent corrosion by applying a negative charge to the metal surface, which can inhibit the electrochemical reaction that causes corrosion. This technique involves attaching a sacrificial anode, usually made of zinc or magnesium, to the metal surface. The anode is then connected to a direct current (DC) power source, which creates a negative charge on the metal surface, preventing corrosion.

Cathodic protection is commonly used for aircraft components that are exposed to seawater, such as the hulls of seaplanes or amphibious aircraft. This technique can be used to prevent corrosion in both aluminum and steel components.

Proper Design and Engineering

Proper design and engineering of aircraft parts and systems can also help to prevent and control corrosion. Designers and engineers can use techniques such as cathodic protection, coatings, and sacrificial anodes to protect aircraft components from corrosion.

Cathodic protection involves using a sacrificial metal or an external power source to protect the metal surface from corrosion. Coatings, as mentioned earlier, can provide a barrier against moisture and other corrosive agents. Sacrificial anodes involve attaching a less corrosion-resistant metal to the metal surface, which will corrode instead of the more critical component.

Therefore, corrosion of aircraft parts poses a significant risk to the safety and reliability of aircraft, which can result in significant economic and safety consequences, increased maintenance costs, and even safety hazards.

By taking a comprehensive approach, manufacturers, and operators can minimize the risk of corrosion and ensure the safety and reliability of the aircraft while also reducing the overall costs associated with corrosion.

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Feature Image: VCV - Victorville boneyard. Photo: Luca Flores/Airways

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