What is corrosion?
A generally accepted definition is: The phenomenon of metal destruction due to the action of the environment with which it is in contact.
Corrosion will not only manifest itself through lack of metal lustre or rust formation, but it may also cause cracks which lead to metal fracture, decrease of ductility or perforation.
While the definition only contemplates metals, it is also true that wood is subject to rot, plastic to swelling and blistering and concrete to lixiviation, due to the action of their surrounding environment. This type of damage might be classified as corrosion, and it certainly will be, once the above mentioned materials are subjected to further studies. However, due to the fact that metal is and has been the most widely used material in plant construction, it has been subject to more extensive studies. Hence, we call corrosion to the particular mechanism which causes metal degradation.
To limit our definition, we must first establish the type of action we are referring to. In many opportunities, a material may break due to mechanical reasons, such as tensile stress. This type of action is precipitated in presence of a corrosive environment, and when the two factors are combined, the case may be encompassed within our definition.
When metal deterioration or destruction is the result of combined mechanical and physical forces, this damage takes place in a shorter period of time than it would have taken in the case of a single independent factor. We shall study corrosion as the global phenomenon. Examples of the latter are: corrosion, stress corrosion, erosion- corrosion, cavitation, etc.