Evaluating inhibitor performance in CO-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 chemicals 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 (SIJ) in CO-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. reduction in weight loss, in-situ corrosion rate behavior and total penetration depth). The results demonstrated the importance of surface analysis techniques when evaluating the performance of chemicals, indicating that weight loss and in-situ electrochemical techniques alone can sometimes provide misleading information on inhibitor performance in laboratory tests. This evaluation is conducted in erosion-corrosion environments where no semi-protective corrosion product formation occurs. AC impedance measurements have also been incorporated into the analysis to assist in interpreting inhibition mechanisms and determine how chemicals can reduce both the erosion and corrosion components of damage.