| The transmission of CO2 is a vital part in Carbon Capture and Storage?CCS?process.However,it is inevitable that some impurities such as H2O,O2,SO2 and H2S will be found in the supercritical CO2 fluid.The presence of theses impurities may increase the corrosion rate of carbon steel,and pose great risk to the security of pipelines.Therefore,to evaluate the corrosion degree and clarify the corrosion mechanism of supercritical CO2 transport pipeline will be conducive to establish the quality specifications of supercritical CO2 fluids and promote the application of carbon capture and storage.To achieve this objective,the simulation experiments under different impurity conditions were conducted in a high temperature autoclave.The corrosion rate of X65 steel used in supercritical CO2transport pipeline was determined through weight loss tests.The morphologies and composition of corrosion scales were characterized by scanning electron microscope?SEM?,energy dispersive spectroscopy?EDS?and X-ray diffraction?XRD?.The main conclusions are as follows:1)In water-unsaturated?3000 ppmv?supercritical CO2 systems,low concentrations of impurities significantly alter the corrosion control process of X65 steels.In the supercritical CO2-H2O system,X65steel is controlled by CO2 corrosion,and the corrosion product is FeCO3.For the supercritical CO2-H2O-O2system,the corrosion products are Fe2O3 and FeCO3;In the supercritical CO2-H2O-SO2 system,CO2corrosion is inhibited,SO2 controls the corrosion process,the corrosion product film is mainly FeSO3hydrate;for supercritical CO2-H2O-O2-SO2 system,SO2 corrosion and oxygen corrosion occurred.At the same time,the synergistic effect of O2 and SO2 promoted the formation of H2SO4 and the recycle reaction of acid.The corrosion products were mainly FeSO4 hydrate and FeOOH.2)The uniform corrosion rate of X65 steel increases with the increase of SO2 concentration in the supercritical CO2-SO2-O2-H2O system with 1000ppmv O2 and 3000 ppmv H2O,but the increase gradually decreases.With the increase of SO2 concentration,the corrosion morphology was gradually connected to the whole plane by scattered plaque deposits.After the pickling of the corrosion samples,it was found that there are local corrosion.The corrosion process is controlled by SO2 in the SO2 concentration range of 125ppmv to 1000 ppmv.Corrosion products are mainly FeSO3·xH2O and FeSO4·xH2O,and FeOOH and Fe oxides.3)In the water-unsaturated supercritical CO2-O2-SO2 system,the corrosion rate increases with the increase of O2 concentration,but increase slowly.Since the solubility of O2 in water is small,the increase of O2 concentration does not change the flower-like morphology of the corrosion products,only the roughness of the plaque deposits is increased.The corrosion products were mainly FeSO3·xH2O,FeSO4·xH2O,and FexOy appeared with the increase of O2 concentration,but the increase of O2concentration had little effect on the corrosion of X65 steel under the experimental conditions.4)The corrosion rate of X65 steel was 19.32mm/y after corrosion 1 h in the water-saturated supercritical CO2 system with 8 MPa,50oC and of 1000 ppmv O2 and 1000 ppmv of SO2.and the corrosion rate decreased rapidly with the increase of corrosion time,The corrosion rate decreased to 0.80mm/y after corrosion for 48 h,and remained at a high level.The growth process of the corrosion product film is the uniform corrosion product film-the appearance of the irregular round-shaped corrosion products-the corpus-shaped corrosion product film is connected,the corrosion product is a double-layer structure,and the surface layer is corrugated.Corrosion film composition is mainly FeSO4 hydrate and FeOOH. |
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