**3. Corrosion inhibitors**

An inhibitor is a substance that, when added in small concentrations to an environment, decreases the corrosion rate. In a sense, an inhibitor can be considered as a retarding catalyst. There are numerous inhibitor types and compositions and are generally classified into organic and inorganic inhibitors (**Figure 2**). Most inhibitors have been developed by empirical experimentation, and many inhibitors are proprietary in nature and thus their composition is not disclosed. The chemicals, their concentration, and the frequency of injection depend on the process medium and, normally, on the recommendations of the inhibitor manufacturer, since these chemicals, although generic in nature, are generally proprietary items [10, 13, 15]. The inhibitors used are normally chromates, phosphates, and silicates, added following the recommendations of the manufacturer. The removal of oxygen from a fluid medium improves the chances of corrosion resistance by materials in contact with the fluid. Controlling and stabilizing the pH value of the medium is another method of combating corrosion Inhibition is not completely understood because of these reasons, but it is possible to classify inhibitors according to their mechanism and composition. The corrosion rates of usefully resistant materials generally range between 1 and 200 mpy [10, 13, 15].
