Mechanistic Role of Surface Roughness on CO₂ Corrosion Kinetics and Pitting Susceptibility of AISI 1020 Carbon Steel

Surface roughness is often cited as a factor in CO₂ corrosion, but its effect is not consistently accounted for, especially when comparing electrochemical and weight-loss results.In this work, AISI 1020 carbon steel with different surface finishes was tested in CO₂-saturated 3 wt.%NaCl at 25 ℃ under stagnant conditions.Corrosion behavior was examined using linear polarization resistance (LPR) over the first 180 minutes, polarization measurements, weight loss over 168 hours, and Scanning Electron Microscopy (SEM).As the surface became smoother, the average roughness, Ra, decreased from 2.652 to 0.448 µm.Over the same range, the corrosion rate from weight loss decreased from 0.92 to 0.58 mm/y, while the average LPR corrosion rate decreased from 1.96 to 0.96 mm/y.Polarization results showed that rougher surfaces had more active corrosion potentials, higher corrosion current densities, and lower polarization resistance.SEM observations also revealed more localized attack and deeper pits on the rougher samples, whereas smoother surfaces were affected mainly by more uniform corrosion.These results suggest that surface roughness affects corrosion mainly by increasing anodic activity and promoting localized dissolution within surface features.The differences between electrochemical and gravimetric results are due to changes at the surface during the early stages of exposure, which are captured by LPR but averaged out in weight-loss measurements.The findings are very important in the oil and gas industry via reducing corrosion.