Evaluating inhibitor performance in CO2-saturated erosion-corrosion environments

Over the last decade, significant advances in chemical inhibition have enabled operators to use carbon steel pipework in oil and gas facilities where sand production is a concern. The ability of these inhibitors to reduce both the electrochemical corrosion reactions and the mechanical damage attributed to particle impingement is well documented, but the underlying mechanisms have been the subject of less attention. This paper presents a review of three commercially available oilfield corrosion inhibitors (two standard corrosion inhibitors and one high shear-resistant inhibitor) in an effort to establish their performance in erosion-corrosion environments. Experiments were conducted at 45° C using a submerged impinging jet in carbon dioxide (CO2)-saturated conditions with a fluid velocity of 14 m/s and sand loading of 500 mg/L. A combination of gravimetric measurements, in situ electrochemistry, and surface profilometry allowed the inhibitors to be assessed based on a number of different parameters (i.e., mass loss, in situ corrosion behavior, and total penetration depth). The results demonstrate the importance of surface analysis techniques when evaluating the performance of inhibitors in erosioncorrosion environments, indicating that mass loss and in situ electrochemical techniques alone can sometimes provide misleading information in relation to their performance. The inhibitors are evaluated in erosion-corrosion environments where no semi-protective corrosion product formation occurs. Electrochemical impedance spectroscopy measurements are incorporated into the analysis to assist in interpreting inhibition mechanisms and to help determine how inhibitors may be capable of reducing both the erosion and corrosion components of material loss.