What is corrosion?Corrosion can be defined as the deterioration of a material due to a reaction with the surrounding environment. Metals corrode because we use them in chemically unstable environments. Very few metals are found in nature in the metallic state such as copper, gold and silver. All other metals are transformed from ores or ores into metals that are inherently unstable in their environments. These unstable metals have a tendency to revert to their more stable mineral forms. Some metals form protective ceramic films (passive films) on their surfaces which prevent, or slow down, the corrosion process. We can prevent corrosion by using metals that form naturally protective passive films, but these alloys are generally expensive, so we have developed other means of corrosion control. We will talk about this later in this document. Types of Corrosion There are two common classifications of corrosion: direct chemical attack and electrochemical attack. In both cases the metal is converted into a compound such as sulfate, oxide or hydroxide. Corrosion always involves two simultaneous changes. The metal that is oxidized undergoes what is called an anodic change and the corrosive agent is reduced and undergoes a cathodic change. Direct chemical attack is corrosion resulting from direct contact of a bare surface with a caustic liquid or gaseous substance. Unlike electrochemical etching where the anode and cathode changes can occur remotely, the changes in direct chemical etching occur at the same time and in the same place. The most common substances that cause a direct chemical attack on an aircraft are; Residual flux deposits resulting from joints not being properly cleaned, soldered, soldered or brazed, poured into the center of paper...aluminum. There are many types of stainless steels. They are generally immune to corrosion, but in some cases they can cause crevice corrosion and suffer stress corrosion cracking. Titanium is a common metal in nature, but its limited use means that small-scale production results in a high price. However, it finds wide use in the aerospace industry. There are two general types of titanium alloys: aerospace alloys and corrosion-resistant alloys. Technical designers must consider the amount of metal needed to resist the expected load for a given application. Because they can make mistakes or the structure can be misused, they are required to over-design the aircraft based on a safety factor. Once the necessary mechanical load safety factor has been considered, it becomes necessary to consider whether what corrosion tolerance is necessary to keep the aircraft safe.