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 film formation and destruction and the corrosion protection mechanism of a carbon dioxide (CO2) corrosion inhibitor, imidazoline. Imidazoline is an inhibitor base which is most commonly used for protecting oil wells, gas wells and pipelines from CO2 corrosion. Typical EIS spectral changes were clearly observed during the inhibitor film formation and destruction processes, and this suggests that EIS is a practical technique for evaluating inhibitor film persistency and for monitoring the inhibitor film performance. EIS data were used to calculate corrosion related electrochemical parameters and EIS was shown to be a very useful tool for studying inhibitor mechanisms. EIS results showed that imidazoline is a very effective CO2 corrosion inhibitor which forms a chemically bonded film on the metal surface. The inhibitor film seems to have 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-repairing ability and good persistency under the testing conditions although surface water shear stress gradually removed the inhibitor film and caused inhibitor film failure after around 170 h under the test regime. Copyright (C) 1996 Published by Elsevier Science Ltd