Influence of Turbulent Flow on the Localized Corrosion Process of Mild Steel with Inhibited Aqueous Carbon Dioxide Systems

• Published in: Corrosion (Houston, Tex.) Tex.), 2002-07, Vol.58 (7), p.608-619
• Main Authors: Mora-Mendoza, J.L., Chacon-Nava, J.G., Zavala-Olivares, G., González-Núñez, M.A., Turgoose, S.
• Format: Article
• Language: English
• Subjects: Ammonium; Ammonium compounds; Anodic polarization; Applied sciences; Carbon dioxide; Cetyltrimethylammonium bromide; Corrosion; Corrosion effects; Corrosion inhibitors; Corrosion potential; Corrosion tests; Cylinders; Electrochemistry; Exact sciences and technology; Fluid dynamics; Inhibitors; Localized corrosion; Low carbon steels; Metals. Metallurgy; pH effects; Rotating cylinders; Rotation; Shear stress; Sodium; Sodium chloride; Steel; Turbulent flow
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3277652

ABSTRACTThree percent sodium chloride (NaCl) solutions saturated with carbon dioxide (CO2) were used to study the corrosion inhibition of mild steel samples under turbulent flow conditions. The performance of cetyl trimethyl ammonium bromide (CTAB) was tested with three different concentrations (20, 60, and 100 ppm) and three different pH values (3.8, 5, and 6). The rotating cylinder electrode (RCE) was used to test different turbulent flow conditions (1,000 rpm to 5,000 rpm). It was found that the inhibitor performance is a function of concentration and pH. A localized corrosion process was found on the surface samples and further research was carried out to determine its causes. With the use of cyclic anodic polarization curves and surface examinations, it was demonstrated that the localized corrosion process does not occur at a specific rotation speed. Potentiostatic experiments simulated the effect of shear stress and the instantaneous changes in corrosion potential (Ecorr) observed when the rotation speed was increased. The electrochemical measurements and surface examinations showed that changes in Ecorr to more positive values are more important in producing the localized process, and removing the electrostatically adsorbed inhibitor from the surface sample, than increases in shear stress.A wide variety of materials have been used as corrosion inhibitors to protect the steel pipelines and process equipment used in the extraction, production, and transport of oil and natural gas. The organic compounds are by far the most common ones used today and are generally considered to be the most effective. Most of the inhibitors in use are organic nitrogen compounds, all of which have long-chain hydrocarbons, usually C12 to C18, as a part of their structure. Quaternary compounds have become very popular since the 1950s because they were found to effectively prevent corrosion of iron and steel in acid solutions. A well-accepted explanation for the inhibitive properties of quaternary amines with straight chains is electrostatic interaction of the positive ion to the negatively charged metal. These inhibitive properties usually improve when organic groups are added that contain lone-pair electrons or -electron systems associated with multiple bonds or aromatic rings, which bond to metal surfaces by electron transfer to the metal to form a coordinate type of link.1 The effect of adsorbed inhibitors on metals in acid solutions is to retard either the cathodic reac