Effect of microstructure on corrosion of steels in aqueous solutions containing carbon dioxide

The influence of microstructure on the corrosion rate of steels in a carbon dioxide (CO2)-containing aqueous solution was measured experimentally as a function of pH, temperature, and partial pressure of CO2. An attempt was made to quantify and relate the microstructure to the corrosion rate. The effect of alloy microstructure was Increasingly evident at temperatures up to 60 degrees C but diminished above 60 degrees C. The corrosion rate increased with temperature In the activation-controlled regime, where a nonprotective iron carbonate (FeCO3) scale formed. Diffusion-controlled corrosion through a stable scale of iron hydroxycarbonate (Fe-2[OH](2)CO3) was responsible for lowering the corrosion rate above 60 degrees C. Under a diffusion-controlled corrosion mechanism microstructure of the steel had no effect on corrosion rate.