Structural parts often go through high stress environment and being metals like steel it is most prone to corrosion. Corrosion is a natural phenomenon when a metal surface undergoes chemical reactions with atmospheric chemical elements and thereby leading to occurrence of corrosion. There are generally 5 types of corrosion that happens to metals. They are: Galvanic, Stress cracking, general, localized & caustic agent corrosion.
This is extraordinarily common type of corrosion occurrence when two metals with different electrochemical charges are linked via a conductive path. Corrosion occurs when the metals move from anodized metal to cathodic metals. Corrosion prevention coating would be applied to prevent the transfer of ions or the condition that causes it. Bimetallic corrosion also occur when an impure metal is present. When a metal corrodes without exposure to electrical current can be termed as general corrosion.
Stress Corrosion Cracking
SCC can seriously damage the component beyond a point of repair. When the metal is subjected to extreme tensile stress, a metal component will experience stress corrosion cracking which forms crack in the grain boundary targeting further corrosion. The main causes could be cold work, welding & thermal treatment. These factors, combined with exposure to an environment that often increases and intensifies stress-cracking, can mean a part goes from suffering minor stress-corrosion to experiencing failure or irreparable damage.
General Corrosion of Metals
It basically occurs as a result of rust due to oxidization of the metal surface with the environment forming a thin layer of rust on the metal surface. Like bimetallic corrosion, general corrosion is also electrochemical. A protective coating helps prevent the oxidation and thus reduce the chances of rust.
It occurs when a small part of component experiences corrosion or comes in contact with the specific corrosion causing stresses. A small area corrodes faster than the rest of the component and the corrosion works alongside the other process such as stress & fatigue. But the end result is, it is much worse than the results of stress & fatigue alone.
Caustic Agent Corrosion
This occurs when impure gas, liquids, or solid wear a material down. Although impure gases don’t damage the metal, when these impure gases come in contact with moisture they form a very harmful corrosive droplets. Hydrogen sulfide is one such example of a caustic agent.
So these are the types of corrosion that can occur to a metal surface and hence care should be taken to prevent the materials from getting corroded.