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SPE International Conference on CO2 Capture, Storage, and Utilization,
10-12 November 2010,
New Orleans, Louisiana, USA
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Abstract
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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