Development of an environmentally safe corrosion, scale, and microorganism inhibitor for open recirculating cooling systems

The use of heavy metal-based corrosion inhibitors is increasingly being curtailed by recent environmental restrictions. In many parts of the world, high levels of inorganic phosphates are also restricted by law. In response to these environmental guidelines, this paper presents the results of a ‘green’ chemicals study that was undertaken to investigate the ability of a new inhibitor to inhibit the corrosion, scale and microorganism problems found in open recirculating cooling systems. This study used a new all-organic multi-component inhibitor blend composed of citric acid/phosphonates (hydroxy ethylidene diphosphonic acid, HEDP)/acrylate copolymer/isothiazolone. The effects of the inhibitor on carbon steel dissolution in synthetic cooling water were studied through weight loss measurements and electrochemical, scale, and microorganism tests. The results obtained from this study show that the new inhibitor can decrease corrosion, scale build-up and microbial growth under the conditions tested. Potentiodynamic polarization curves indicate that the blended inhibitor acted as an anodic inhibitor, reducing metal dissolution. The nature of protective films formed on the carbon steel was studied by scanning electron microscopy (SEM) and auger electron spectroscopy (AES). The inhibition effects are due to the formation of protective films which might contain calcium phosphonates and iron oxide. The inhibitor used in this study appears to have an excellent crystal modification effect on calcium carbonate scale. The various microorganisms used in this study were inhibited effectively in the planktonic state.