Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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18 SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM MATERIAL MATTERS to reduce potential risks and transport of sc-CO 2 in a cost-effective manner. Water is the most common impurity in sc-CO 2 . Water may originate from the combus- tion of carbohydrates and/or moisture from the air. According to the research- ers, studies show that the solubility of H 2 O increases as the pressure and tem- perature of the sc-CO 2 stream increases. While H 2 O-induced corrosion is negligi- ble, the presence of water is a preliminary factor for pipe steel corrosion in sc-CO 2 streams due to its synergistic effects with other corrosive impurities. Another ty pical impurity in sc-CO 2 is O 2 as a fossil-fuel combustion residual, particularly in oxy-fuel combustion plants. Additionally, O 2 can be introduced into the pipelines from pressure compen- sation pumps during sc-CO 2 transporta- tion. While O 2 only has a marginal effect on corrosion in sc-CO 2 , both iron oxides and iron(II) carbonate (FeCO 3 ) were Continued f rom page 17 found on pipe steel samples after expo- sure to sc-CO 2 that contained H 2 O and O 2 . If the corrosion process is dominated by electrochemical reactions, the presence of O 2 is expected to enhance the cathodic reaction. In coal-f ired power plants, SO 2 is pro- duced and, therefore, present in the cap- tured CO 2 gas mixture. But the role of SO 2 in sc-CO 2 is still unclear, the researchers comment. Most studies indicate that the simultaneous presence of H 2 O, O 2 , and SO 2 can cause severe corrosion of pipe steels. The corrosion products usually consist of iron sulf ite (FeSO 3 ), sulfate, and oxides, but there is no clear idea of how the corrosion rates would be affected by the presence of SO 2 because of the con- f licting results reported by different groups. H 2 S is found in sc-CO 2 streams cap- tured using pre-combustion technolog y. The sulf ide ion (S 2- ) has a strong aff inity to pipe steels, so resulting corrosion prod- ucts are usually composed of complex iron sulf ides. Only a few studies were con- ducted to investigate the effect of H 2 S on corrosion in sc-CO 2 , and most research found that corrosion rates obtained were less than 0.19 mm/y, even with up to 2,000 ppm of H 2 S in the sc-CO 2 stream. This, according to the researchers, implies that the addition of H 2 S alone is not likely to result in severe corrosion of pipe steels in H 2 O-saturated sc-CO 2 . This may be due to the formation of a compact iron sulf ide layer that protects the substrate in the sc-CO 2 streams. However, when b oth O 2 and H 2 S are present in H 2 O-saturated sc-CO 2 , a remarkable increase in corro- sion can be expected. Most organic impurities in sc-CO 2 originate from CO 2 capture solvents, absorbers, or corrosion inhibitors. Their effects on corrosion will be either positive or negative, depending on the chemistry of the organics. For example, monoetha- nolamine (MEA), a widely used CO 2 absorber, can noticeably reduce the cor- rosion rate as a corrosion inhibitor. Several other knowledge gaps were identif ied by Zeng, Araf in, Luo, and Li. They note that it is important to clarif y whether the corrosion in the sc-CO 2 stream is controlled by electrochemical or gas phase reactions so long-term corrosion prediction models can be developed. References 1 "Carbon Capture and Storage," International Energy Agency, https://www.iea.org/topics/ carbon-capture-and-storage (August 13, 2018). 2 "What Is Carbon Capture and Storage?" Na- tional Energy Technology Laboratory, U.S. Department of Energy, https://www.netl . d o e . g o v / re s e a r c h / c o a l / c a rb o n - st o ra ge / c a r b o n - s t o r a g e - f a q s / w h a t - i s - c a r b o n - capture-and-storage (August 13, 2018). 3 Y. Zeng, K. Li, J. Luo, M. Arafin, "Impacts of Impurities on Corrosion of Supercritical CO 2 Transportation Pipeline Steels," CORROSION 2018, paper no. 11481 (Houston, TX: NACE International, 2018). —Kathy Riggs Larsen Environmentally Safe VpCI ® /MCI ® Technologies EXCELLENCE Q U A I T Y ® C O R P O R AT I O N

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