Wettability of carbon steel and carbon steel with corrosion product films (iron carbonate
(FeCO3) and FeCO3 with oxidized surface) was investigated through contact angle and
inhibitor performance tests. Two corrosion inhibitors, an oleic imidazoline compound (OI)
and a phosphate ester compound (PE) were used. The inhibitor performance was studied in
CO2 corrosion tests at 60 ºC, 1 bar CO2, 3 Wt-% NaCl and 20 vol-% oil, where the samples
were alternately exposed to oil and aqueous phase. A refined, low aromatic, oil was used in
the tests.
Addition of both surfactants lead to significant changes in the wettability of oxidized FeCO3
surfaces. The contact angle tests showed that a transition from a preferential water-wet
state to a preferentially oil-wet state was achieved for both inhibitors.
Electrochemical measurements revealed that addition of OI enabled the oxidized FeCO3
surface to retain an oil film after exposure to oil. The retained oil film caused a significant
drop in corrosion rate in the presence of oxygen. The effect was also seen on a rusting
carbon steel surface without any surface deposits. No similar effect was seen for PE.
Keywords: Corrosion inhibitor, wetting, hydrophobic, iron carbonate, rust, FeCO3