Corrosion Control (I): Corrosion-Resistant Steel and Cement

To mitigate CO2-induced corrosion of steel, a practical approach is to replace normal steel with CO2-resistant steel alloys. The most common CO2-resistant steel alloy is chromium (Cr)-bearing steel alloy, which has a Cr content of 2–27 wt%. To further enhance the resistance of Cr-bearing alloys to the attack by CO2 and other sour gases, other metals like nickel (Ni), molybdenum (Mo) and titanium (Ti) can be added to the alloys. One of the most effective cement slurry systems against CO2 corrosion is the composite cement system with phosphoaluminates. Aluminate cement and phosphate cement have higher CO2 corrosion resistance than ordinary Portland cement, because the minerals and chemical components of aluminate cement and phosphate cement are different from those of ordinary Portland cement. Another type of anti-CO2 corrosion cement is cement with inorganic or organic additives. Common inorganic anti-CO2 corrosion additives include nanoclays, nano silica, Fe2O3, etc. Micro-CT assessment of wellbore cement with CO2-modified nanoclay showed that the expansion of heavy carbonation areas in cement was restricted after 28 days CO2 corrosion.