Aircraft, just like any other complex metal system, are susceptible to corrosion. As parts of aircraft are also made up of various types of metals, aircraft corrosion is inevitable. Corrosion does not just affect the plane's appearance, but also its performance and its subsequent reliability as well. In this blog, we will discuss what aircraft corrosion is and the different types one may face.
What Is Aircraft Corrosion?
The rusting of metal surfaces and parts of any plane is called aircraft corrosion. The rusting of an aircraft happens when the unprotected metal comes into direct contact with the oxygen present in the atmosphere. Rusting is bound to happen, which is why airline companies regularly clean and paint their airplanes to delay the onset of corrosion as much as possible. High moisture levels, exposure to pollutants, and substandard preparation before painting are a few factors that may cause an aircraft to corrode. Depending on what causes corrosion, the location of corrosion, and what it looks like, there are several types of aircraft corrosion airline companies have to deal with.
Types of Aircraft Corrosion
The most commonly seen type of aircraft corrosion is surface corrosion. It mostly occurs when the metal present on an aircraft's surface starts to oxidize. This happens when metal parts are exposed to air for a long period of time. This can be due to exposure to high humidity situations or even a poor paint job. Things like unfavorable environmental conditions, the use of harsh chemicals, and poor quality paints can accelerate the speed of surface corrosion. However, surface corrosion is easy to detect and predict, hence, diagnosing and preventing it is also easier as compared to other types of aircraft corrosion.
Dissimilar Metal Corrosion
Dissimilar metal corrosion in aircraft is seen when disparate metal parts are in contact with each other in the presence of an electrolyte or a conductor. Dissimilar metal corrosion, or electrochemical corrosion, is a type of corrosion that causes extensive pitting damage to aircraft parts. It usually cannot be seen as it takes place out of sight, making it fairly troublesome. Treating dissimilar metal corrosion can be very expensive if it goes unnoticed for a long period of time. Usually, the only way to check if this type of corrosion has taken place is by disassembling and inspecting various parts.
Intergranular corrosion is a localized type of aircraft corrosion that is an attack on the grains that make up the metals and alloys of an airplane. It affects an alloy’s grain boundaries and is related to the absence of uniformity in the alloy structure. Intergranular corrosion usually exists without any surface evidence. However, it may lead to the lifting and flaking of metal surfaces over time. Extruded components of aircraft are particularly more prone to intergranular corrosion. Normally, this type of corrosion is seen in 7000-series alloys (alloys that have a substantial amount of zinc, such as stringers and wing spars).
Stress corrosion occurs in the parts of the aircraft that have to bear a lot of stress. It generally develops in parts like engine crankshafts and landing gear that are constantly put under tensile stress in corrosive environments. Being in sustained tensile stress environments can lead to cracking, and even failure. A few things that cause this type of corrosion in airplanes are tapered bolts, externally-applied cyclic loading, and press-fit bushings. Shot-peening of metal surfaces, protective coatings, and stress-relief heat treatments are some of the ways that one can prevent the occurrence of stress corrosion.
Concentration Cell Corrosion
Also known as crevice corrosion, this type of aircraft corrosion occurs when water gets caught between different surfaces. Concentrated cell corrosion is a dangerous type of aircraft corrosion as it can rapidly lead to pitting or exfoliation corrosion.
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