The influence of inhibitors molecular structure and steel microstructure on corrosion layers in CO2 corrosion -: An XPS and SEM characterization

Morphological and compositional studies were conducted on the corrosion layers formed on carbon steel with two different heat treatments in chloride media containing CO2 by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The performance of three imidazoline-like compounds as corrosion inhibitors was analyzed. Amino-propylimidazol (API) and two commercial imidazoline-based products (PC and QB) were used with this purpose. The corrosive media was a deoxygenated 5% NaCl solution, CO2 saturated at pH 6 at 40 degreesC. XPS results indicated that, independently of the steel microstructure, FeCO3 was present among the corrosion products when API and PC were used, while an inhibitor protective film formed with the addition of QB. However, the ratio of the various compounds present was influenced by the microstructure of the base material. On the other hand, it is concluded that the molecular structure of the compounds employed as inhibitors seems to have a main role on their performance in the studied experimental conditions. (C) 2004 Elsevier B.V. All rights reserved.