Abstract
Corrosion inhibition is an essential tool for assuring asset integrity in oil and gas transportation. Consequently, research related to organic surfactant-type inhibitors, which adsorb on a metal surface to form a protective layer against corrosion, is of great interest to the oil and gas industry. Conventional thinking, as conceptualized in the open literature, has the decrease in corrosion rates due to inhibitor addition directly related to surface coverage. However, research studies have so far not provided direct evidence of such a link; this is primarily due to the limitations of conventional electrochemical techniques used to investigate them. In the present research, in situ atomic force microscopy (AFM) coupled with electrochemical measurements has been used to study surface coverage by a tetradecyldimethylbenzylammonium inhibitor model compound; it possesses 14 carbon atoms in its hydrophobic tail (Q-C14). Application of AFM elucidates physical attributes of the inhibitor adsorption morphology and provides information which cannot be obtained by traditional electrochemical techniques alone. Analysis of AFM data indicates that the adsorbed inhibitor film likely exists as a self-assembled layer. AFM imaging results showed that the surface coverage on mild steel was closely related to inhibitor bulk solution concentration. When the bulk solution inhibitor concentration was below the surface saturation value, AFM measurements indicated partial coverage of the surface by the inhibitor film and patchy corrosion of the metal surface was observed; this has the potential to result in localized attack. When inhibitor bulk concentration was above the surface saturation value, full surface coverage was detected by AFM measurements and corrosion was uniformly retarded.
