A flow loop study on the effect of Ca 2+ ions on the CO 2 corrosion of 1Cr carbon steel in a CaCO 3 -saturated solution

Abstract

This paper investigates the effect of calcium on the CO₂ corrosion behaviour of 1Cr carbon steel under the effect of flow. The experiments were performed in a flow loop system in 1 wt-% NaCl solution at 80°C, pH = 6.34 with initial S _CaCO3 = 2 and pCO₂ = 0.53 bar. The flow velocity was kept at 3 m s⁻¹ and the system was pressurised to 3 bar. The corrosion process was monitored with linear polarisation resistance and electrochemical impedance spectroscopy (EIS). Phase analysis of the corrosion products was obtained using X-ray powder diffraction and surface morphology was characterised with scanning electron microscopy. Results show that the flow delayed the precipitation of substitutional solid solution of Fe_0.31Ca_0.69CO₃, deferring the pseudo-passivation stage. The flow did not cause Mesa attack or localised corrosion. The protectiveness of this film was not affected by the presence of calcium and was comparable to the one of pure FeCO₃.