|Content Type||Conference Paper|
|Title||Effect of Water Content On the Corrosion Behavior of Carbon Steel In Supercritical CO2 Phase With Impurities|
|Authors||Yoon-Seok Choi, Institute for Corrosion and Multiphase Technology, Department of Chemical and Biomolecular Engineering, Ohio University; Srdjan Nešić, Institute for Corrosion and Multiphase Technology, Department of Chemical and Biomolecular Engineering, Ohio University|
|Source||CORROSION 2011, March 13 - 17, 2011 , Houston, Texas|
|Copyright||2011. NACE International|
|Keywords||Supercritical CO2, CO2 corrosion, H2O, O2, SO2, carbon steel, carbon capture and storage|
Sufficient drying (water removal) of carbon dioxide (CO2) in transport pipelines is required to prevent breaking-out of free water and consequent excessive corrosion rates. The drying requirement for CO2 pipelines, used for enhanced oil recovery (EOR) in the United States, is a maximum of 650 ppm (mole) of water. However, there is a possibility of increased corrosion rates in supercritical CO2 phase with water vapor (below its solubility level) in the presence of oxygen (O2) and sulfur dioxide (SO2). Thus, the objective of the present study is to evaluate the corrosion properties of carbon steel in supercritical CO2/O2/SO2 mixtures with different amounts of water (under-saturated) related to the transmission of CO2 to sequestration sites. The corrosion property of carbon steel was evaluated by using an autoclave operating at different pressures (maximum 2000 psi), temperatures (maximum 50°C), and concentrations of O2 and SO2 impurities as well as water content. The corrosion rate of samples was determined by weight loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed using surface analytical techniques (scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD)).
It is well known that dry CO2 does not corrode carbon steels generally used for pipelines, as long as the relative humidity is less than 60%.1 Thus, sufficient drying (water removal) upstream of the pipeline is standard practice in order to prevent excessive corrosion rates.2,3 The drying requirement for CO2 pipelines, for example, used for enhanced oil recovery (EOR) in the United States, is to a maximum of 650 ppm (mole) water.4 This further increased to more than 7 mm/y with addition of both O2 and SO2.6 These results indicated that corrosion can take place in the water-saturated supercritical CO2 phase in the presence of impurities. Water-saturated supercritical CO2 is both highly diffusive, due to its low viscosity, and highly reactive owing to the potentially enhanced acidic nature of water dissolved in the dense CO2 phase containing impurities. Recent research7 showed that water solvated in liquid and supercritical CO2 is quite reactive towards the steel surface under conditions that approximate those anticipated for CO2 transport. No corrosion was observed on carbon steel in liquid CO2 with 610 ppmw water at 62 bar and 22oC for 42 days. With 998 ppmw water, however, corrosion product formed on the steel over 21 days at the same working pressure and temperature. Water solubility in liquid CO2 at 63 bar and 22oC is approximately 1100 ppmw, this implies that corrosion occurs in the liquid CO2 phase when under-saturated with respect to water. In addition, it suggests that there is a threshold water content for onset of corrosion. Other research8 claimed that the corrosion rate of carbon steel in the presence of a small quantity of water (1000 ppm) in supercritical CO2 was 1 mm/y at 79 bar and 31oC. Furthermore, even with water content lower than Kinder Morgan specification (650 ppm), there is a possibility for corrosion at certain conditions.
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