Corrosion of Coated Cast Iron in Aqueous Solutions

Abstract

The effectiveness of various coatings and their combination on cast iron is studied under various experimental conditions, like period of immersion, temperature, and flow velocity of corrosive medium, using weight loss and potentiostatic polarization measurements. Various coatings offer protection according to their binding capacity, porosity, environmental conditions, and penetration of ions to the metal surface through coating. The corrosion rate enhance with increase in period of exposure and flow velocity, whereas at high temperatures it does not show a sharp alteration. Negligible corrosion is observed on specimens coated entirely with rubber coating (RC), paint over reel oxide coating (RO+PC), coal tar epoxy resin (CTER), coal tar zinc rich epoxy resin (CZER), and 1/3 RC + 1/3CTER + 1/3 CZER. Reel oxide (RO) is, however, anticorrosive, providing protection in composite water studies but is unable to prevent the penetration of water. Hot galvanized coating (HGC) is found to provide better protection than cold galvanized coating. Half-coated specimens are corroded more and therefore are not suitable for use in water supply systems.