CO2 Corrosion Behavior of Calcite-Covered API 5L X52 Carbon Steel in Aqueous Solutions

The CO2 corrosion of API 5L X52 steel in the presence and absence of calcite scale has been investigated. The scale was precipitated from a supersaturated solution at temperatures of 25 and 80 degrees C. The crystalline phase, cross section and surface morphologies of scale were studied by x-ray diffraction and scanning electron microscopy, respectively. It was found that the scale deposit mostly consisted of calcite. The corrosion behavior of bare and calcite-covered samples was investigated by electrochemical impedance spectroscopy and cyclic polarization techniques in aqueous CO2 solutions at 30, 50 and 70 degrees C. The presence of calcite scale on carbon steel surface decreased the adsorption of intermediate corrosion products as the scale uniformly covered the bare surface which resulted in reduction of general CO2 corrosion rate. The results of cyclic polarization tests revealed that the bare and calcite-covered samples were not susceptible to localized CO2 corrosion under conditions studied in this research.