AN INVESTIGATION OF THE FORMATION AND DESTRUCTION OF CORROSION-INHIBITOR FILMS USING ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY (EIS)

Electrochemical impedance spectroscopy (EIS) was used to study the fil m formation and destruction and the corrosion protection mechanism of a carbon dioxide (CO2) corrosion inhibitor, imidazoline. Imidazoline i s an inhibitor base which is most commonly used for protecting oil wel ls, gas wells and pipelines from CO2 corrosion. Typical EIS spectral c hanges were clearly observed during the inhibitor film formation and d estruction processes, and this suggests that EIS is a practical techni que for evaluating inhibitor film persistency and for monitoring the i nhibitor film performance. EIS data were used to calculate corrosion r elated electrochemical parameters and EIS was shown to be a very usefu l tool for studying inhibitor mechanisms. EIS results showed that imid azoline is a very effective CO2 corrosion inhibitor which forms a chem ically bonded film on the metal surface. The inhibitor film seems to h ave a multi-layered structure which is a combination of an inner layer , which may be an inhibitor-metal complex layer, and many outer layers of inhibitor molecules. The inhibitor film showed strong self-repairi ng ability and good persistency under the testing conditions although surface water shear stress gradually removed the inhibitor film and ca used inhibitor film failure after around 170 h under the test regime. Copyright (C) 1996 Published by Elsevier Science Ltd