Corrosion of Carbon Steel in Dense Phase CO2 with Water above and Below the Solubility Limit

Abstract

Few experimental studies have addressed corrosion under dense phase CO2 transport conditions and very different corrosion rates (CR) are reported for apparently the same concentration of impurities (i.e. water) in the CO2 stream. The differences reflect short-comings in the experimental methodology and demonstration the need for a commonly agreed test approach.An experimental set up allowing accurate control of the water concentration was developed and used in the present work, which provides a more realistic condition mimicking the situation in the operating pipelines. Five corrosion experiments were conducted at 95bar to determine the corrosion rate of carbon steel in CO2 with various concentration of dissolved water. The water concentration was increased stepwise from 100 ppmv to the solubility limit and the limit was also exceeded in one of the experiment. The temperature was varied between 8°C and 35°C.The general corrosion rates determined by weight loss were around 1.0μm/y and no localised attacks were observed as long as the water content was below the solubility limit or exceeding the solubility limit with 10 percent for 400hours. The results indicate that the corrosion rate of carbon steel will be negligible in the CO2-water system as long as the water is kept below the solubility limit. The presence of other impurities than water will change the condition for precipitation of corrosive aqueous phases.