Application of corrosion inhibition in upstream oil and gas production is the way protect carbon steel against internal process corrosion. Test methods have been developed that mimic field conditions and test corrosion inhibitors (CI). Testing includes long-term (500 hr) tests to evaluate local effectiveness. A test program typically includes validation of CI performance at several conditions to qualify for its full operating range. This includes impact of water chemistry, acidic gasses (CO2 and/or H2S), temperature, shear stress, etc.
Validation and interpretation of test results can sometimes be complicated. Corrosion rates are generally reported based on weight loss, visual assessment and linear polarization resistance (LPR) measurements. These results often lead to a pass/fail outcome without providing insight into the protection mechanisms and failure modes.
Electrochemical impedance spectroscopy (EIS) is an electrochemical measurement technique that may help to reveal protection mechanisms and provide insight for optimisation of CI testing and application. For this reason, EIS measurements were introduced in support of standard CI test methods. This work outlines the results, provides interpretation and identifies the benefits and limits of using EIS. Based on the results guidelines are formulated for using EIS. The results revealed CI protection/failure mechanisms under specific test conditions.
Key words: Corrosion Inhibition, Electrochemical Impedance Spectroscopy, Corrosion Inhibitor Testing, Wall Shear Stress, Scaling.