Alteration of Wettability of Corroding Carbon Steel Surface by Carbon Dioxide Corrosion Inhibitors-Effect on Carbon Dioxide Corrosion Rate and Contact Angle

The wettability of the steel surface is an important factor co-determining the risk of corrosion in multiphase pipelines for transportation of oil and gas. The effect of carbon dioxide (CO2) corrosion inhibitors on the wettability of carbon steel was investigated in the present paper. Also investigated was the effect of oil on the performance of these inhibitors. Three inhibitors were investigated. Two of them were commercial inhibitor-based chemicals: an oleic imidazoline salt (OI) and a phosphate ester (PE). The third was cetyltrimethylammonium bromide (CTAB). a well-characterized quaternary ammonium compound. A refined, low-aromatic oil product was used in the tests. The wettability of the corroding carbon steel surface was studied by contact angle measurements (25 degrees C, 1 bar CO2, 3 wt% sodium chloride [NaCl]). Both oil-in-water and water-in-oil experiments were performed. The effect of the inhibitor/oil interactions were also studied in CO2 corrosion tests where the steel specimens were alternately exposed to oil and the aqueous phase. The performance of OI and PE was significantly improved by the presence of oil. These inhibitors also enhanced the oil wettability of the steel surface, while CTAB enhanced the water wettability.