Effects of Crude Oil on Corrosion Behavior of Pipeline Steel under Wet CO2 Condition

Abstract The wet CO2 corrosion is a complex process, especially when crude oil is contained in the corrosion system. In this paper, the corrosion behaviors of 3Cr alloy steel, L245 and 16Mn steel in oil-water mixture emulsion with 10%, 30%, 80% water cut under various temperature in a dynamic condition were investigated, respectively. The corrosion product scale was characterized by SEM and EDS. The results demonstrate that 3Cr steel exhibited the best corrosion resistance. At 10% and 30% water cut, the corrosion scales of the three steels were thin and compact, and dominated by FeCO3. At 80% water cut, a Cr-rich layer formed on surface of 3Cr steel, and the scale of L245 steel was compact internal but porous external, while the scale of 16Mn steel was compact but cracked and spalled. The corrosion rate of 3Cr steel decreased with increasing temperature at 80% water cut, but the corrosion rate of 16Mn steel increased sharply with increasing temperature due to the corrosion scale spalled. The corrosion rate of L245 steel exhibited a maximum value at 60 °C. Combined the morphologies of scales and the corrosion rate, it can be found that the corrosion rates of three steels increased obviously when the solution changed from water-in-oil to oil-in-water, but the Cr element caused a reduction of corrosion rate at high temperature and high water cut by forming Cr-containing layer. However, pitting corrosion formed under the thin and cracked Cr-containing layer.