An experimental and theoretical investigation of the influence of surface roughness on corrosion in CO2 environments

The influence of surface roughness on the rate of corrosion in CO2 environments without film formation is investigated both experimentally and theoretically. The former measurements are obtained using the linear polarisation resistance technique on a rotating cylinder electrode apparatus with four different samples with roughness 0.5, 6, 20 and 34μm. Experimental measurements of corrosion rate for smooth and rough surfaces are compared against predictions from a modified form of a mechanistic CO2 corrosion model [1], where mass transfer coefficients are specified using a new correlation for rough surfaces [2]. Test conditions selected for comparison consisted of a CO2-saturated 1 wt.% NaCl brine at 25oC covering pH values between 4 and 6. X65 carbon steel samples were used as working electrodes, with rotational rates varying from 1000 to 4000 rpm. Agreement between experimental and theoretical corrosion rates is good and demonstrates clearly how increased surface roughness accentuates corrosion rates and mass transfer coefficients, and that the latter need to be accounted when implementing theoretical models.