Types of Aircraft Corrosion

Every aircraft owner knows corrosion can mean serious trouble to an airplane. But, not every aircraft aficionado is familiar with the different types and forms of corrosion that can cause damage. Here’s everything you need to know about corrosion you could encounter on your aircraft:

Different Types of Corrosion

Aircraft corrosion typically falls under one of two categories: direct chemical attack or electrochemical attack. Although these two types of corrosion are different, they do share one similarity. Both types of corrosion produce a reaction which turns the metal into a metallic compound.
Direct chemical attacks are also known as pure chemical corrosions, and occur when a bare metal surface is exposed to caustic liquids or gases. The most common liquids and gases that cause a chemical corrosion on aircrafts are battery acid or fumes from the batteries, flux deposits, and harmful cleaning solutions that are trapped in the aircraft’s crevices.
Battery acid is becoming less of a problem since many newer models of planes use closed battery units that prevent the acid from spilling out. However, many types of fluxes that are used in welding, brazing and soldering parts of the plane are corrosive and can cause serious corrosion. To prevent this type of corrosion from occurring, it is important for aircraft owners to carefully remove any residual flux from the external surface of the plane after use.  To avoid corrosion caused by cleaning agents, it is advised that aircraft owners only use noncorrosive cleaning solutions on the areas where liquid can be easily trapped.
Electrochemical attacks are the second type of corrosion that can occur on an aircraft. This attack requires a medium, usually water, which can conduct a tiny current of electricity. The attack can occur when a metal is exposed to a corrosive agent and the medium with the electricity current, the metal will begin to decay and corrosion will occur. All metals have a specific electric potential, known as a metal’s “nobility.” The less electric potential the metal has, the more easily it will corrode when exposed to an electrochemical attack. To prevent this type of corrosion from occurring, aircraft owners must make an effort to make sure no electric mediums, such as water, are present on the aircraft. Without the medium, an electrochemical attack cannot occur, and therefore cannot cause corrosion.

Different Forms of Corrosion

There are a number of different forms of corrosion that can appear on an aircraft. Perhaps the most common form is surface corrosion. If you notice any signs of roughening, etching or pitting on the metal surface of your aircraft, you may be dealing with surface corrosion, especially if you notice a fine, powdery substance on the surface as well.
However, some types of surface corrosion are not as easily identifiable. For example, instead of a rough surface, you may notice the paint is beginning to chip or lift off of the plane’s surface. Or, you could notice little bumps underneath the paint’s surface that look like tiny worms. Both of these are signs of surface corrosion and should be treated as soon as possible with a metal polish designed to remove corrosion, scratches and oxidation.
Dissimilar metal corrosion is another form that is common on metal aircrafts. This form can cause pitting damage to the surface of the aircraft and occurs when two or more different metal parts make contact with each other and a conductor, such as water, at the same time. If you’ve ever had to deal with dissimilar metal corrosion, you know just how dangerous and costly it can be to detect and repair. Unlike surface corrosion which is fairly easy to spot, dissimilar metal corrosion often goes undetected for prolonged periods of time. In fact, many times the corrosion goes unnoticed until it has gotten so bad that it causes structural failure. The only way to detect this form of corrosion before it has caused such serious damage is to completely disassemble the inspect the parts.
Aircraft owners can take one precaution to avoid dissimilar metal corrosion. When cleaning the external surface of the plane, be careful while using steel wool or steel wire brushes. These may seem harmless, but tiny pieces of metal may come off of these cleaning tools and force their way into the surface of the plane, increasing the likelihood that dissimilar metal corrosion will occur. If you use abrasive pads while cleaning the plane, never use the same pad on different types of metal. If your aircraft has two types of metal, then use two separate pads—one for each type—to avoid dissimilar metal corrosion.

What aircrafts are at risk of corrosion?

Any metal aircraft is at risk of developing corrosion, which is why it’s so important to implement a regular maintenance and cleaning schedule. However, there are certain types of aircrafts which are known to be more prone to corrosion than others, such as any Cessna aircraft built between the years 1977 and 1982. When Cessna switched to a new type of polyurethane paint, they did not follow the manufacturer’s recommendations for protecting the metal. Because of this error, these aircrafts are known to be susceptible to worm-like filiform corrosion which typically starts underneath the paint.

How can you remove corrosion?

Now that you know the different types and forms of corrosion, stock up on the products you need to keep your aircraft in perfect condition. Luckily, corrosion can be removed from the external surface of an aircraft with the help of the right airplane polish. The right kind of metal polish can remove heavy oxidation, corrosion and scratches from the surface of the plane, making it look brand new and preventing any safety issues that can result from excessive corrosion. Polish can also prepare the aircraft’s surface for a layer of protective paint or coating. If you notice any signs of corrosion on your aircraft’s surface, make sure you use polish to remove it as soon as possible to prevent further damage.