An inhibitor is a substance that slows down a chemical reaction (in the present context, a corrosion reaction). Corrosion inhibitors are commonly added in small amounts to acids, cooling waters, steam, and many other environments--either continuously or intermittently--to reduce the intensity of corrosion that might otherwise threaten the intended design life of a structure. The use of chemical inhibitors to decrease the rates of corrosion processes is quite varied. In the oil extraction and processing industries, corrosion inhibitors have always been considered to be the first line of defense against corrosion. A great number of scientific studies have been devoted to the subject of corrosion inhibitors. Nevertheless, rules, equations, and theories to guide inhibitor development and use are very limited. Most of what is known has grown from trial-and-error experiments, both in the laboratories and in the field. The degree of corrosion protection may not be proportional to the amount of inhibitor in all concentrations. Therefore, it is always important to evaluate the concentration of inhibitor that provides the optimal ratio of benefits to cost.
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