Properties and Effects of Water-Soluble Inhibitors on the Corrosion Rates of Structural Metals

Abstract

The effects of six commercial water-soluble inhibitor formulations on the corrosion rates of aluminum and steel in seawater were determined. Corrosion rates were measured by the weight loss of specimens following long-term immersion in artificial seawater containing inhibitors at the developer’s recommended dosages. The effects of environmental changes on inhibitor behavior were also investigated by varying the seawater concentration in certain tests. Surface plasmon resonance (SPR) spectroscopy was investigated as a method to observe the inherent adherence and persistence of the inhibitors at a metal surface. Results show that the level of effectiveness of the test inhibitors varies significantly and is dependent on the nature of the metal being protected. While some inhibitors reduce the corrosion of steel by up to 80%, others actually increase the corrosion rate. Four of the six inhibitors were observed to increase aluminum pitting; the other two offered protection. Two of the inhibitors reduced the corrosion rates for the aluminum and steel. Surface plasmon resonance spectroscopy was able to detect and discriminate between inhibitors. These measurements show good correlation between the adherence of an inhibitor to a metal surface and its ability to reduce corrosion rates. Results of this study provide a firm measure of the levels of corrosion control that can be achieved by commercially available inhibitor formulations. They also provide a quantitative basis for comparison and selection of corrosion inhibitors for use in a variety of applications (i.e., metal holding tanks and cans, recirculation loops, and modified wash downs of outdoor equipment typically experiencing deterioration due to exposure to salt-containing environments).