RESEARCH OF CAST IRON IN ACIDIC MEDIUM IN THE INDUSTRIAL FIELD AS COMPONENTS IN ACID PICKLING

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. INTRODUCTION TO CAST IRON Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due to its carbide impurities which allow cracks to pass straight through. Grey cast iron is named after its grey fractured surface, which occurs because the graphitic flakes deflect a passing crack and initiate countless new cracks as the material breaks. Carbon (C) and silicon (Si) are the main alloying elements, with the amount ranging from 2.1 to 4 wt% and 1 to 3 wt%, respectively. Iron alloys with less carbon content are known as steel. While this technically makes these base alloys ternary Fe-C-Si alloys, the principle of cast iron solidification is understood from the binary iron-carbon phase diagram. Since the compositions of most cast irons are around the eutectic point of the iron-carbon system, the melting temperatures closely correlate, usually ranging from 1,150 to 1,200 °C (2,102 to 2,192 °F), which is about 300 °C (572 °F) lower than the melting point of pure iron. International Journal of Research in Science And Technology http://www.ijrst.com/ (IJRST) 2011, Vol. No. 1, Issue No. I, Apr-Jun ISSN: 2249-0604 International Journal of Research in Science And Technology Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads (declining usage), cylinder blocks and gearbox cases (declining usage). It is resistant to destruction and weakening by oxidation (rust).