Corrosion inhibitors in brief

A corrosion inhibitor may be defined as a substance which, when added in small amounts to a normally corrosive medium, reduces the corrosion rate of the metal by action at or near the metal surface1. In order to identify a given substance as a corrosion inhibitor it is important to specify both the metal and the environment. It follows that a given inhibitor may be ineffective, or even aggressive, if the metal and/or the environment is changed. The application of corrosion inhibitors is common in variety of industrial fields such as storage and transportation facilities, oil and natural gas production, oil refineries, heat exchangers, condensers, desalination plants as well as cooling water installations, etc. Corrosion inhibitors are routinely used in oil production at varying rates. Many of the commercial corrosion inhibitors are unique mixtures that may contain surfactants, film enhancers, demulsifiers, or an oxygen scavenger in addition to the inhibitor moiety. The majority of corrosion inhibitors used in petroleum production is having nitrogen containing inhibitor moieties and can be classified into the following categories

1. Amides/ imidazolines
2. Salts of nitrogenous molecules with carboxylic acids
3. Nitrogen quaternaries
4. Polyoxyalkylated amines, amides and imidazolines
5. Nitrogen heterocyclic

 There are other, non-nitrogenous inhibitors that contain phosphorous, sulphur, or oxygen atoms but they are used less frequently.