Electrochemical and corrosion behavior of carbon steel in SULFIRAN® process

Corrosion behavior of carbon steel was evaluated in Fe-EDTA solution designed to be used in acid gas treatment process (SULFIRAN® plant) in the temperature range between 35 °C and 45 °C. Electrochemical techniques, i.e. polarization curves and electrochemical impedance spectroscopy (EIS) were applied for laboratory evaluations. Linear polarization resistance (LPR) and weight loss techniques were used to determine the corrosion rate for pilot tests. In addition, several surface analysis techniques such as XRD, XRF, SEM and optical microscopy were employed to determine the corrosion morphology. Metallurgical and SEM investigations of the carbon steel corrosion showed corrosion-induced damages in SULFIRAN® process. The corrosion demonstrated in the forms of severe uniform corrosion, wide shallow pits formation, under deposit corrosion, hydrogen micro-void formation, and hydrogen induced disbonding between the interfaces of the inclusion (MnS) and metal matrix. The corrosion rate of carbon steel alloy is predicted to be very high (>200 mils per year or mpy) in this process.