Effects of CaCO 3 deposits on the corrosion behaviour of N80 carbon steel under simulated oilfield water conditions

In this study, the effects of CaCO 3 deposition on the corrosion behaviour of N80 carbon steel were investigated under simulated oilfield water conditions, with particular attention paid to its dual role in either promoting or inhibiting corrosion. The electrochemical experiments were conducted in both a NaCl + NaHCO 3 single corrosive solution and a NaCl + NaHCO 3 + CaCl 2 corrosive scaling solution at atmospheric pressure and the temperature of 30 °C. The flow rates of 200 r/min and 0 r/min were used to simulate dynamic and static environments, respectively. Meanwhile, scanning electron microscopy and X-ray diffraction were employed to analyse the microscopic morphological features, and composition of the corrosion products. The results indicated that the N80 carbon steel surface mainly exhibited uniform corrosion in single corrosive solution. When the scaling ion Ca 2+ was introduced, the corrosion current density increased by 3.422 × 10 −5 A/cm 2 (29.3%) and 1.775 × 10 −5 A/cm 2 (77.4%) in dynamic and static environments, respectively. This suggests that the uneven CaCO 3 deposits formed a galvanic cell with the exposed substrate, which exacerbated localised corrosion. Additionally, the corrosion current densities further increased by 2.982 × 10 −5 and 0.384 × 10 −5 A/cm 2 in solutions without CaCO 3 . The presence of CaCO 3 deposits on the sample surface prevented dissolved oxygen and Cl − ions in the solution from reaching the substrate, thus inhibiting overall corrosion.