Cast iron is the common metallic material being used for numerous applications in a variety of industries as well as in daily life. Cast iron is commonly used in fabrication of reaction vessels, storage tanks by industries, sinks, hose pipe lines, automobiles, etc. because of its low cost and reasonably good strength. Hydrochloric acid is the most difficult to handle from the standpoints of corrosion. Extreme care is required in the selection of materials to handle the acid by itself, even in relatively dilute concentrations or in process solutions containing appreciable amounts of hydrochloric acid. Most of severe corrosion problems encountered involve the mineral acids or their derivatives. Cast iron corrodes when it comes in contact with aggressive environment. Corrosion inhibitors are added to the corroding medium in small concentration to control the corrosion rate of metals and alloys. In general, any phase constituent whose presence is not essential to the occurrence of an electrochemical process, but leads to a retardation of this process by modifying the surface state of the metallic material will be called an inhibitor. In a sense, an inhibitor can be considered as a retarding catalyst. Acid corrosion inhibitors find wide application in the industrial fields as components in acid pickling, acid cleaning, oil well acidizing, acid desalting etc. Most of the efficient inhibitors used in industry are organic compounds having multiple bonds in their molecule which are adsorbed on metal surface. There are numerous inhibitor types and compositions. Most inhibitor has been developed by empirical experimentation and many inhibitors are proprietary in nature and thus their composition is not disclosed.

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