| Carbon capture and storage technology can significantly reduce carbon emissions and is widely considered by the international community as one of the most critical technologies for responding to global climate change and controlling greenhouse gas emissions.Due to cost and transmission efficiency,CO2 is usually transported by pipeline.Because the CO2 gas source comes from different industries such as power plants,chemical plants,coal mines,etc.,it is unavoidable to contain trace impurity components,which are important factors in induc-ing potential corrosion of CO2 transport pipelines.In recent years,studies on the effect of impurities on the corrosion behavior of CO2 pipelines have focused on factors such as impu-rity types and impurity concentrations.However,the effects of environmental factors such as temperature,pressure,and flow rate play an important role in the corrosion behavior during transportation.Therefore,it is necessary to study the influence of environmental factors in the transport process on the corrosion behavior.In this paper,X65 steel was used as the experimental material and the thermodynamic model of the mutual solubility of H2S impurities was established.Through the combination of corrosion simulation experiments and modern surface analysis techniques,the effect of the different pipelines site and saturated moisture content,temperature,pressure change,and flow velocity was systematically studied in the supercritical CO2-H2O-H2S system containing sat-urated water on corrosion behavior of X65 steel.The main findings are as follows:?1?Based on the thermodynamic equation of state of Redlich-Kwong,a thermodynamic model for the solubility of supercritical CO2-H2O-H2S was established based on the thermo-dynamic model of CO2-H2O mutual solubility.The calculation results show that the solubility change of water phase in the supercritical CO2-H2O system containing H2S impurity is con-sistent with that in the absence of impurity.When 1000 ppmv of H2S impurity was added,the solubility of the water phase in the system appeared to decrease.The addition of H2S impurity can change the solubility of water phase in supercritical CO2 fluid and promote the precipita-tion of water phase.?2?In the water-saturated supercritical CO2-H2O-H2S system containing 1000ppmv H2S with temperature at 50°C and pressure at 8 MPa,the corrosion rate of the top specimen of the simulated pipeline was higher than that of the sidewall and bottom specimens of X65steel after 48h corrosion test.With the corrosion time extended to 120h,the film thickness and compactness of the corrosion product formed on the surface of X65 steel increased,and the corrosion rate of the top sample was gradually consistent with the corrosion rate of other parts of the simulated pipeline.The general corrosion rate of X65 steel increases logarithmically with the increase of saturated water content in the supercritical CO2-H2O-H2S system.?3?In the water-saturated supercritical CO2-H2O-H2S system containing 1000ppmv H2S,X65 steel is most severely corroded at a temperature of 35°C and a pressure of 8 MPa.The corrosion rate was measured by the rate of change of the corrosion rate with changes in temperature and pressure.The results showed that the temperature change had less effect on the corrosion of the X65 steel in the supercritical CO2-H2O-H2S system,and the corrosion rate was more sensitive to system pressure changes.As the pressure increases,the corrosion sensitivity gradually decreases.Calculating the density of the corrosion system,it was found that the density and corrosion rate of the corrosion system are consistent in different condi-tions.However,the instability thermodynamic properties of CO2 at the critical temperature and pressure makes the corrosion rate at a temperature of 35°C and a pressure of 8MPa not meet this requirement the changing trend.?4?In the supercritical CO2-H2O-H2S system containing 1000 ppmv H2S and 10g H2O,the general corrosion rate of X65 steel first increased and then decreased with the flow rate.The size of spherical FeS crystals attached to the surface of micro-etched products on X65steel increased first and then decreased with the increase of flow rate.The spherical corrosion products are densely distributed and uniform in size at a flow rate of 1 m/s.The variation of the relative content of FeS in the corrosion product with the flow rate is consistent with the variation of the size of the spherical FeS corrosion product with the flow rate variation.The density and viscosity coefficient of the supercritical CO2 fluid in the corrosive system increase dramatically at a temperature of 35°C and a pressure range of 7.5MPa to 8.5MPa.The wall shear stress of the X65 steel formed in the supercritical CO2-H2O-H2S system is not enough to peel off the corrosion scale from matrix,but the morphology of the corrosion product film was affected,resulting in a moire-like corrosion characteristic. |
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