Influence of temperature on the corrosion behavior of API-X100 pipeline steel in 1-bar CO2-HCO3− solutions: An electrochemical study

This paper addresses on the influence of temperature, elucidated with a number of electrochemical methods and immersion tests, on the corrosion behavior of API-X100 steel in CO2-saturated bicarbonate solutions. Investigated by cyclic potentiodynamic polarization, the corrosion rates, which showed a sensible increase with 10 g L−1 (0.16 mol L−1), 30 g L−1 (0.5 mol L−1) and 50 g L−1 (0.82 mol L−1) bicarbonate concentrations, increased from about 500, to 1500 and 1800 μA cm−2 at 20, 50 and 90 °C, respectively. Passivation at 50 and 90 °C showed resistance to deteriorate against 100 ppm chloride ions, of which anodic 0.5 V vs. SCE peaks exclusively appeared. Moreover, transpassivation occurred at 0.9 and 0.7 V vs. SCE, respectively, unlike with the 20 °C cases whose chloride-induced-pitting-vulnerable, gradually-forming passive films transpassivated at 1 V vs. SCE. At different potentials, the potentiostatic currents increased with temperature, but their profiles suggested more effective passivation, accordingly. The charge transfer resistance, calculated by electrochemical impedance spectroscopy, decreased with temperature at the open circuit potentials and 0.6 V vs. SCE, where the interfacial interactions were governed by adsorption, and diffusion-limited processes, respectively.