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PublisherNACE InternationalLanguageEnglish
Document ID 09256
Content TypeConference Paper
TitleCORROSION BEHAVIOR OF CARBON STEEL IN SUPERCRITICAL CO2-WATER ENVIRONMENTS
AuthorsYoon-Seok Choi, Srdjan Nešić, Institute for Corrosion and Multiphase Technology Department of Chemical Engineering Ohio University
SourceCORROSION 2009, March 22 - 26, 2009 , Atlanta, GA
Copyright2009. NACE International
Keywordssupercritical CO2, thermodynamic modeling, CO2 corrosion, carbon steel
PreviewABSTRACT:

 The corrosion behavior of carbon steel was investigated under supercritical CO2 (scCO2) - water systems to simulate the condition of CO2 transportation pipeline in the CO2 sequestration applications. To understand the thermodynamic properties of scCO2-water systems related to the corrosion phenomena, thermodynamic modeling were conducted to determine the mutual solubilities of CO2 and water in the two coexisting phases, and to calculate the concentrations of corrosive species in the free water at various pressures and temperatures. Carbon steel samples were exposed to water-saturated CO2, and CO2-saturated water in the pressure range of 40 to 80 bar at 50oC. The corrosion rate of samples was determined by weight loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed by using surface analytical techniques (SEM and EDS).



INTRODUCTION:

 The capture and storage of CO2 in geological reservoirs is now considered to be one of the main options for achieving deep reductions in greenhouse gas emissions.1,2 The CO2 capture and storage process involves three stages: capture of the CO2 from the power plant or industrial process, transmission of the CO2 to the storage site followed by injection into the geological reservoir.3 In order to avoid two-phase flow regimes and increase the density of the CO2, the captured CO2 gas is typically compressed to the supercritical state while the temperature and the pressure are over 31.1oC and 73.8 bar, respectively, thereby making it easier and less costly to transport.3,4 The research activities are largely concentrating on development of the capture technology to reduce costs, and on assessing the technical feasibility of injecting and monitoring the CO2 within the geological reservoirs themselves.5 Little of the research is being conducted on CO2 transmission, but this remains a critical component that should not be overlooked. Low alloy carbon steel pipelines have been used for transportation of CO2 at high pressure, but in all cases, CO2 must be dried to eliminate the corrosion risk.6 However, if CO2 transport is to be achieved at a large scale or in existing pipelines, it will not be practical to dry it sufficiently and liquid water “breakout” is to be expected. Furthermore, drying CO2 contributes to an increase in handling cost, especially for offshore installations where weight allowance and space for process equipment installation are very restricted.7 When free water exists in the pipeline, it will be saturated with CO2 and the corrosion rate will be significant for carbon steel because of the formation of carbonic acid (H2CO3). In addition, even though pure, dry supercritical CO2 is not corrosive, there are several studies which provide qualitative evidence for corrosion on carbon steel in water-saturated supercritical CO2 phase.8,9 Thus, to be able to consider the corrosion risk in such pipelines, quantitative evaluation of corrosion in both CO2-saturated water and water-saturated CO2 phases will be needed. The impact of CO2 corrosion on carbon steel has been studied extensively at pressures relevant for oil and gas transport (up to 20 bar CO2).
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