Role of Ca2+ in the CO2 corrosion behavior and film characteristics of N80 steel and electroless Ni-P coating at high temperature and high pressure

Abstract The effects of Ca2+ on the CO2 corrosion behavior and film characteristics of N80 carbon steel and electroless Ni-P coating at high temperature and high pressure were investigated by immersion tests, in-situ electrochemical measurements, surface characterization techniques and water chemistry analysis. The results demonstrate that the corrosion of N80 steel is significantly influenced by Ca2+ concentration, however Ni-P coating exhibits exceptional corrosion resistance regardless of Ca2+ concentration. The microstructure and compactness of FeCO3 corrosion film is altered with the increased incorporation of Ca2+, thereby affecting the electrolyte penetration and the corrosion rate consequently. The added Ca2+ also impacts the water chemistry of the aqueous phase, postponing the FeCO3 precipitation. Meanwhile, the superb corrosion resistance of Ni-P coating is owing to the protection of the formed NiO/Ni(OH)2 film and the absence of scale formation.