Corrosion by CO2 causes significant metal loss when compared with equivalent pH acid system, because, unlike proton reduction in conventional acid-based corrosion, there is a concomitant reaction here, stemming from direct reduction of un-dissociated carbonic acid. Given that carbonic acid is weakly ionizing acid, oxidizing and corroding potential of acidic CO2 system is significant.

Experience shows that if the liquid water quantity in stream is limited and the system consistently operates above the dew point, high CO2 partial pressures can be handled in carbon steel equipment. However, when water condensation occurs, corrosion rates of steel due to carbon dioxide corrosion can be in range of 10 to 20 mm/yr. Therefore, appropriate phase behavior modeling, including ionic descriptions of different, relevant components and system speciation is an important aspect of this and any corrosion study.

In the present case of CCS, the stream can also contain "trace" compounds such as SO2, NOx and Hg that arise from fossil fuels and their combustion. Interactions between the species involved in "normal" carbon dioxide corrosion and these stream constituents pose an extreme risk of corrosion to steel and possibly certain corrosion resistant alloy (e.g.13Cr through alloy 825) equipment and which is not predicted by commonly used corrosion prediction methodologies.

Oil and gas industry has accumulated substantial experience and material technology to mitigate CO2 corrosion, which includes substantial laboratory data collected at high temperature and pressure conditions in service environments. In addition, corrosion models have been developed for assessment of service environments, phase behavior and effects of impurities, along with corrosion prediction and alloy selection that are widely used in the petroleum industry.

The paper addresses the following aspects of corrosion-related challenges to CCS equipment and systems, specifically focusing on the metallic materials employed for the service:

  1. Predominant corrosion/cracking mechanisms and other materials issues resulting from implementation of CCS processes.

  2. Relevant and current practices and experience relative to corrosion control and materials selection and the impact of variations in process conditions.

  3. Materials and corrosion research gaps analysis for optimizing materials performance of CCS systems.

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