A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a corrosion inhibitor depends on fluid composition, the quantity of water, and flow regime. A common mechanism for inhibiting corrosion involves the formation of a coating, often a passivation layer, which prevents access of the corrosive substance to the metal. Permanent treatments such as chrome plating are not generally considered inhibitors, however. Instead, corrosion inhibitors are additives to the fluids that surround the metal or related object.
Corrosion inhibitors are common in the industry, and also found in over-the-counter products, typically in spray form in combination with a lubricant and sometimes a penetrating oil.
Illustrative applications
Volatile amines are used in boilers to minimize the effects of acid. In some cases, the amines form a protective film on the steel surface and, at the same time, act as an anodic inhibitor. An inhibitor that acts both in a cathodic and anodic manner is termed a mixed inhibitor.
Benzotriazole inhibits the corrosion and staining of copper surfaces.
Corrosion inhibitors are often added to paints. A pigment with anticorrosive properties is zinc phosphate. Compounds derived from tannic acid or zinc salts of organonitrogens (e.g. Alcophor 827) can be used together with anticorrosive pigments. Other corrosion inhibitors are Anticor 70, Albaex, Ferrophos, and Molywhite MZAP.
Antiseptics are used to counter microbial corrosion. Benzalkonium chloride is commonly used in oil field industry.
In oil refineries, hydrogen sulfide can corrode steels so it is removed often using air and amines by conversion to polysulfides.
Fuels industry
Corrosion inhibitors are commonly added to coolants, fuels, hydraulic fluids, boiler water, engine oil, and many other fluids used in industry. For fuels, various corrosion inhibitors can be used. Some components include zinc dithiophosphates.
DCI-4A, widely used in commercial and military jet fuels, acts also as a lubricity additive. Can be also used for gasoline and other distillate fuels.
DCI-6A, for motor gasoline and distillate fuels, and for U.S. military fuels (JP-4, JP-5, JP-8)
DCI-11, for alcohols and gasoline containing oxygenates
DCI-28, for very low-pH alcohols and gasoline containing oxygenates
DCI-30, for gasoline and distillate fuels, excellent for pipeline transfers and storage, caustic-resistant
DMA-4 (solution of alkylaminophosphate in kerosene), for petroleum distillates.
