Influence of sodium hexa metaphosphate antiscalant on the corrosion of carbon steel in industrial cooling water system

Abstract

In order to have clear understanding about the contribution of antiscalant and zinc ions separately towards the corrosion control of carbon steel in six different synthetic cooling waters, a single antiscalant, sodium hexa meta phosphate (SHMP), was tried with and without zinc ions, which may control scaling as well as corrosion problem in cooling water system (CWS). Weight loss, electrochemical polarization and metallurgical research microscopy technique were carried out at 30, 40 and 50°C using different concentrations of the inhibitor and zinc ions. Mechanism of inhibition is explained on the basis of molecular structure of the inhibitor. The inhibitor provides good inhibition efficiency and acts as anodic inhibitor when present alone and mixed inhibitor with zinc ions. SHMP due to its cyclic structure, forms cage-complex with Fe²⁺ ions from any two adjacent negatively charged phosphoryl oxygen anions. Moreover, addition of zinc ions to cooling water along with SHMP, do not increase inhibition efficiency to an appreciable extent.