Development of Phosphate Based Inhibitors Effective for Oxygen Corrosion: A Study of Localized Corrosion Inhibition Mechanism

Abstract In general, oilfields have less gas pressure as they mature. As a result, ingress of oxygen into well annuli, into the vapor space in tanks, and through pump packing becomes more commonplace. Consequently, it is possible for severe localized corrosion (> 12 mm/y) to occur. Localized corrosion is the main corrosion regime imposed by the presence of oxygen. This paper reveals a study by electrochemical impendence spectroscopy to understand this phenomenon. An attempt to assign the physicochemical phenomenon responsible for the inductance behavior observed, is discussed. Upon the inhibition of corrosion, electrochemical impedance spectroscopy is used to understand the characteristics of the inhibition mechanism. Phosphate esters do not form corrosion inhibitor films as compact as the films formed by imidazoline-based inhibitors, which act through a geometric coverage mechanism. Instead, this study supports the view of phosphate esters acting through a deactivation coverage mechanism. In this work, we report an improved performance of the second generation of novel phosphate ester based inhibitors. These corrosion inhibitors are capable of reducing corrosion to more than 96 % and also reducing pitting corrosion to a minimum. This demonstrates the capacity to protect carbon steel from the carbonic acid induced corrosion in the presence of high oxygen levels.