Corrosion of transport pipelines for CO2–Effect of water ingress

Both field experience and lab data indicate that the corrosion rate of carbon steel in pure dense phase CO2 is near zero if no free water is present. The question is whether this also applies when other contaminants like SOx, NOx, H2S and O2 are present in moderate amounts. In a pipeline network with different types of CO2 sources, the commingling of streams with various impurities can give a very complex mixture, and side reactions like oxidation and decomposition of impurities can be foreseen. An important issue is how the contaminants partition between the various phases during pressure reduction and when free water is present. The corrosion mechanisms under these conditions are not well understood, and it becomes more and more uncertain what will happen when the concentration of contaminants including water increases. The paper addresses these issues and discusses recent corrosion flow loops and autoclaves results obtained in an ongoing sub-sea CO2 transmission pipeline project.