Corrosion and passive behavior of carbon steel in hydrogen sulfide (H2S)-containing diethanolamine (DEA) and diglycolamine (DGA) solutions were investigated using Tafel polarization and electrochemical impedance spectroscopy (EIS) techniques. Solutions were made using industrial-grade DEA or DGA and sour water. Tafel polarization results showed that passive films are formed in both DEA and DGA solutions. X-ray analysis showed that the passive film formed in DEA solution is troilite (FeS), an iron sulfide with high stoichiometry. Conversely, a non-stoichiometric iron sulfide named mackinawite (FeS1–x) was formed in DGA solution. EIS results showed that the corrosion in the DEA solution is diffusion-controlled and that in DGA solution is charge-transfer-controlled. The corrosion rate of carbon steel in H2S-containing DEA solution was found to be lower than the DGA solution in the same conditions. Obtained results showed that the corrosion rate of steel increases with increased amine (DEA or DGA) concentration.

Subject
Electrochemical impedance spectroscopy, Ions, Hydrogen concentration, Corrosion rate, Diffusion, Iron sulfides, Passive films, Sulfide films, Impedance, Constants, Amines, Film formation, Carbon steel
Keywords:
carbon steel, corrosion, corrosion resistance, impedance, passivation, polarization curve
NACE International
2009
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