Study of Crevice Corrosion Behavior and Its Mechanism of Carbon Steel in Simulated Oilfield Produced Fluid

Abstract

For studying the crevice corrosion behavior and mechanism of Q235 carbon steel under different crevice widths and environmental temperatures, wire beam electrode (WBE) technology and electrochemical impedance spectroscopy (EIS) technology were used to study the differences in current density, polarization resistance, and corrosion morphology of wire beam electrodes. Results showed that when the crevice width was greater than 0.1 mm, the corrosion characteristics of the crevice were not obvious. When the crevice width was 0.1 mm, the maximum current density differences of carbon steel during the initial immersion at 25, 40, and 60 ℃ were 1.24, 19.90, and 7.20 μA/cm2, respectively, while the maximum current density differences after 72 h of immersion were only 41.9%, 4.2%, and 11.9% of the initial immersions. In addition, the polarity conversion phenomenon of current occurred both inside and outside the crevice, indicating that Q235 carbon steel gradually transformed from local corrosion to uniform corrosion with the prolongation of immersion time. Moreover, increasing temperature could enhance the trend of crevice corrosion, and the causes of the most serious corrosion outside the crevice were insufficient soaking time and an increase in solution resistance drop. In general, FeOOH participating in the cathodic reaction caused the electrode to change from the anode to the cathode, while the dissolution reaction of the metal caused the electrode properties changing from the cathode to the anode.

Keywords

• q235 carbon steel|wire beam electrode|crevice width|temperature|corrosion mechanism