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°C but diminished above 60°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 (Fe₂[OH]₂CO₃) was responsible for lowering the corrosion rate above 60°C. Under a diffusion-controlled corrosion mechanism, microstructure of the steel had no effect on corrosion rate.