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

Abstract

In this study, the effects of CaCO₃ 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 + NaHCO₃ single corrosive solution and a NaCl + NaHCO₃ + CaCl₂ 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 Ca²⁺ was introduced, the corrosion current density increased by 3.422 × 10⁻⁵ A/cm² (29.3%) and 1.775 × 10⁻⁵ A/cm² (77.4%) in dynamic and static environments, respectively. This suggests that the uneven CaCO₃ 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/cm² in solutions without CaCO₃. The presence of CaCO₃ deposits on the sample surface prevented dissolved oxygen and Cl⁻ ions in the solution from reaching the substrate, thus inhibiting overall corrosion.