Further Investigation on the Effect of Corrosion Inhibitor Actives on the Formation of Iron Carbonate on Carbon Steel

Many studies have been conducted on the action of corrosion inhibitors on corrosion product layers.  There are varying opinions: the inhibitor may preferentially interact with the metallic surface or the existence of a corrosion scale enhances inhibitor adsorption.   This paper will address the effect of the type of corrosion inhibitor active on the growth of iron carbonate.  Our paper presented at NACExpo 2008 explored the synergistic interaction a quaternized amine compound has with iron carbonate.  This work is a continuation and examines how imidazoline, quaternized pyridine and phosphate ester compounds have on iron carbonate.  Tests were performed using the Rotating Cylinder Electrode (RCE) technique in conjunction with LPR (Linear Polarization Resistance), Tafel studies and EIS (Electrochemical Impedance Spectroscopy).  Test samples composed of 1018 carbon steel were exposed to a pH 6.5 CO₂-purged brine environment for the duration of the test.  SEM/EDS (Scanning Electron Microscopy/Electron dispersive Spectroscopy) and XRD (X-ray Diffraction) was used in the analysis of the corrosion samples in order to observe the morphology, thickness and crystal structure of the iron scale layer.  This work will provide insight on how various types of corrosion inhibitor actives affect the growth of iron carbonate.