The study of under deposit corrosion of carbon steel in the flowback water during shale gas production

Serious under deposit corrosion could occur in the shale gas flowback water environment. In this work, under deposit corrosion of Q235 carbon steel in a simulated CO2/O2-containing shale gas flowback water was studied using wire beam electrode, potentiodynamic polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results show that there is a galvanic corrosion effect between the deposit-covered electrode and bare electrode. The polarity of the deposit-covered electrode and bare electrode is reversed at 3 h. Before 3 h immersion, deposit-covered electrode acts as cathode and bare electrode acts as anode. However, after 3 h immersion, deposit-covered electrode turns into anode while bare electrode converts into cathode. The obvious localized corrosion characteristics can be observed under deposit and the corrosion products mainly consist of Fe2O3, Fe3O4 and FeCO3. WBE can be used to in situ monitor the occurrence and development of local corrosion under deposit. The current maps of WBE show that severe local corrosion has occurred on the electrodes covered by deposit. © 2020 Elsevier B.V.