Effect of temperature on the 3Cr low-alloyed steel initial corrosion behavior in CO2 solution

The initial corrosion behavior of 3Cr low-alloyed steel in sodium chloride (NaCl) solution with 0.3 MPa CO2 was systematically investigated at various temperatures. Electrochemical measurement revealed that the corrosion potential of this alloy exhibits a negative shift with increasing temperature, resulting in an increase in corrosion current and decrease in linear polarization resistance (Rp) with increasing temperature. Subsequent electrochemical impedance spectroscopy analysis showed that the amount of adsorbed intermediate corrosion product and amorphous scale also decreased with increasing temperature, which was confirmed by a field emission scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) analysis. Through comparison of electrochemical measurement results with thermodynamic calculation of the ionic concentration and equilibrium electrode potential, it was found that the anodic reaction of 3Cr low-alloyed steel in CO2 solution consists of three main reactions: the direct dissolution of Fe, and the formation of FeCO3 and Cr(OH)3. Analyzing the morphology, composition and structure of the initial corrosion product layer under various temperatures, it is believed that a double corrosion layer forms at low temperatures of 30-50 °C, but a single corrosion layer forms at high temperatures of 70-90 °C.