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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17 MATERIALS PERFORMANCE: VOL. 57, NO. 9 SEPTEMBER 2018 Information on corrosion control and prevention MATERIAL MATTERS Corrosion of Steel Pipelines Transporting Captured Carbon Dioxide for Storage C arbon dioxide (CO 2 ) is the primary greenhouse gas emitted into the planet's atmosphere from fossil fuel combustion. According to the Interna- tional Energ y Agency (Paris, France), "Carbon capture and storage, or CCS, is a family of technologies and techniques that enable the capture of carbon dioxide (CO 2 ) from fuel combustion or industrial processes, the transport of CO 2 via ships or pipelines, and its storage underground, in depleted oil and gas f ields and deep saline formations." 1 The CO 2 , which is separated from industrial process emissions prior to being released into the atmosphere, is captured and usually compressed into a supercritical state (supercritical CO 2 or sc-CO 2 ) before long-distance transport by pipeline to its storage destination in deep underground geologic formations. 2-3 Depending on CO 2 sources and the capture/separation technologies used, the transported sc-CO 2 stream can con- tain some aggressive impurities that could lead to extensive corrosion of pipe steels as well as cracking, say researchers Yimin Zeng and Muhammad Araf in with CanmetM ATERIA LS (Hamilton, Ontario, Canada), and Jingli Luo and Kaiyang Li with the Department of Chemical and Materials Engineering at the University of A lberta (Edmonton, A lberta, Canada). They studied public and in-house corro- sion data on the effects of several ty pical CO 2 impurities to further the fundamen- tal understanding of steel pipeline corro- sion in sc-CO 2 environments, as well as identif y knowledge gaps for further inves- tigation. Their f indings were presented during a CORROSION 2018 symposium in Phoenix, Arizona, USA. 3 Zeng, Araf in, Luo, and Li, all members of NACE International, note that pipeline transportation is recog- nized as the most cost-effective and rela- tively safe conveyance solution for CCS, as it can transport large amounts of CO 2 under predetermined and controlled con- ditions. Ty pically, microalloyed carbon steels (e.g., A PI 5L Grades X60, X65, and X80) are used for constructing sc-CO 2 pipeline networks. From a corrosion point of view, the researchers say, pure sc-CO 2 is not a threat to pipeline integrity. As an example, transportation of CO 2 for enhanced oil recovery has demonstrated that the pipeline corrosion is negligible as long as the CO 2 is pure and impurity con- tent is controlled. Because of differences between the two systems, such as different operating conditions and service environment chemistry, the knowledge and experience from enhanced oil recovery CO 2 pipelines cannot automatically be applied to sc-CO 2 transportation pipelines. In CCS, the transported high-pressure sc-CO 2 streams always contain varying amounts of corrosive agents, such as water (H 2 O), oxygen (O 2 ), sulfur dioxide (SO 2 ), hydro- gen sulf ide (H 2 S), nitrogen dioxide (NO 2 ), organics, etc., that are present in the CO 2 sources and applied capture/separation technologies. The supercritical point for pure CO 2 is 7.38 MPa and 31.4 °C. Both gas and liquid CO 2 are transferred into a uni- form supercritical state above this pres- sure and temperature. The presence of the impurities, though, can change the supercritical point. The presence of impu- rities results in an increase in critical pressure and—except for NO 2 , H 2 S, and SO 2 —a decrease in critical temperature. Thorough removal of these impurities is impractical because of extremely high costs and energ y consumption, so impuri- ties are usually controlled to be within certain ranges to mitigate potential cor- rosion damage and public safety risks. The researchers found that the effects of these impurities on corrosion of CCS transportation pipelines are not clear because of very limited f ield experience, scarce laboratory corrosion data, and conf licting published results. The researchers report that a general consensus has not been established on the allowable limits of impurity contents Continued on page 18

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