Different Types of Corrosion
There are many different types of corrosion which can be classified by the cause of the metal’s chemical deterioration. There are at least 9 types of common metal corrosion, which will be explained one by one. The first one is the general one, or as we called general attack corrosion. This is the most common type and is caused by a chemical or electrochemical reaction which results in the deterioration of the entire exposed surface of a metal. However, this corrosion is considered a safe form. If general attack corrosion attack the entire surface, localized corrosion commonly attacks one area of the metal structure. The third one is called galvanic corrosion or dissimilar metal corrosion, which occurs when two different metals are located together in a corrosive electrolyte. The fourth one is environmental cracking. This corrosion process can be resulted from a combination of environment conditions affecting the metal, such as temperature and chemical. The fifth one is flow-assisted corrosion which is happened when a protective layer of oxide on a metal surface is dissolved or removed by wind or water, exposing the metal to further corroding.
Intergranural corrosion is the sixth type. It is a chemical or electrochemical attack on the grain boundaries of a metal, which often occurs due to impurities in the metal which tend to be present in higher contents near grain boundaries. The seventh one called de-alloying, or selective leaching. It is the selective corrosion of specific element in an alloy. The most common type of this corrosion is de-zincification of un-stabilized brass. The result is a deteriorated and porous copper. The next type is fretting corrosion that occurs as a result of repeated wearing, weight and/or vibration on an uneven, rough surface. This corrosion is often found in rotation and impact machinery, bolted assemblies and bearings, as well as to surfaces exposed to vibration during transportation. And finally, the last one is high-temperature corrosion. This is usually caused by compounds during combustion which is formed by several factors, for instance fuels used in gas turbines, diesel engines and other machinery which contain vanadium or sulfates. These compounds are very corrosive towards metal alloys usually resistant to high temperatures and corrosion, including stainless steel.