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 c arbon dioxide (CO2)-containing aqueous solution was measured experimen tally as a function of pH, temperature, and partial pressure of CO2. A n attempt was made to quantify and relate the microstructure to the co rrosion rate. The effect of alloy microstructure was Increasingly evid ent at temperatures up to 60 degrees C but diminished above 60 degrees C. The corrosion rate increased with temperature In the activation-co ntrolled regime, where a nonprotective iron carbonate (FeCO3) scale fo rmed. Diffusion-controlled corrosion through a stable scale of iron hy droxycarbonate (Fe-2[OH](2)CO3) was responsible for lowering the corro sion rate above 60 degrees C. Under a diffusion-controlled corrosion m echanism microstructure of the steel had no effect on corrosion rate.