Effect of Surface Roughness on Static Corrosion Behavior of J55 Carbon Steel in CO2-Containing Geothermal Water at 65 °C

The influence of surface roughness on the static corrosion behavior of J55 carbon steel in CO2-containing geothermal water environment was investigated with respect to average corrosion rate, morphology, chemical composition, corrosion depth, and the cross section of corrosion products. The influence of surface roughness on the CO2 corrosion of J55 carbon steel was then proposed based on the understanding of corrosion at 65 °C. The results show that the static corrosion rate of J55 carbon steel in CO2-containing geothermal water increases with increasing surface roughness. The surface roughness of J55 carbon steel increases 5.3-fold and the CO2 corrosion rate increases by 1.4-fold under different exposure times. The static corrosion rate of J55 carbon steel in CO2-containing geothermal water changes with exposure time. The corrosion rate of J55 carbon steel decreases with the increase in exposure time, and there is little change in the corrosion rate after immersion for 2 days. At the initial stage of corrosion, the corrosion rate of J55 carbon steel was mainly affected by surface roughness. The greater the roughness, the greater the corrosion driving force and the corrosion reaction surface area and therefore the greater the corrosion rate of J55 carbon steel. After immersion for 2 days, a continuous corrosion product layer was formed on the surface of J55 carbon steel and the corrosion rate was mainly affected by the corrosion product layer. The corrosion products of J55 carbon steel are not altered by surface roughness in a CO2-containing geothermal water environment. The corrosion products of J55 carbon steel are FeCO3 and a minute amount of CaCO3.