Corrosion Behavior Of X65 Steel In Water-saturated Supercritical CO₂-H₂O-NO₂ System

Carbon capture and storage?CCS?technology is a key technology that can effectively cope with global climate change and achieve long-term CO₂ emission reduction.Compressing the CO₂ stream to supercritical state and transporting it through pipelines is the most economical and efficient method of transportation.However,due to the limitations of technology and economics,the collected CO₂ stream will inevitably contains some impurities.Thus,the pipeline may be corroded and there is a certain safety risk in the course of transportation.Therefore,it is necessary to study the potential corrosion of impurities on supercritical CO₂ transport,and it is necessary to further evaluate the degree of corrosion and to thoroughly discuss the laws and mechanisms of corrosion,which can provide theoretical support and technical support for the subsequent application of CCS technology.X65 steel was used in this study which is supercritical CO₂ transport pipeline in CCS technology.To achieve this objective,the simulation experiments under different conditions?time,flow rate,temperature,pressure,etc.?were conducted in a high temperature autoclave in where NO₂ was the main research impurity.The corrosion behavior of X65 steel in water-saturated supercritical CO₂-H₂O-NO₂ system was studied scientifically combined scanning electron microscope?SEM?,energy dispersive spectroscopy?EDS?and X-ray diffraction?XRD?.The main conclusions are as follows:?1?In the water-saturated supercritical CO₂-H₂O-NO₂ system,different degrees of local corrosion of X65 steel were occurred:spherical or bubbling corrosion product accumulated on the surface of the sample,and local etch pits were formed below these accumulated products.At the same time,NO₂ severely inhibited the dissociation of H₂CO₃,and the corrosion process was mainly controlled by NO₂ corrosion.The corrosion products mainly include FeOOH and iron oxides?Fe₃O₄ and Fe₂O₃?in this process.?2?In the static and dynamic?1m/s?water-saturated supercritical CO₂-H₂O-NO₂ system,the corrosion evolution process of X65 can be divided into three stages.With the increase of time,the average corrosion rate drastically decreased at first,then slowed down,and stabilized gradually.However,the average corrosion rate of X65 steel remained at a relatively high level.in general.Especially,the corrosion rate under dynamic conditions?flow rate 1 m/s?is approximately 3 times that in static conditions at 120 h.?3?In the water-saturated supercritical CO₂-H₂O-NO₂ system containing 1000 ppmv NO₂,flow rate had a significant effect on the corrosion rate.The flow rate did not change the composition of the corrosion product film,but changes the morphology of the corrosion product film.?4?In the water-saturated supercritical CO₂-H₂O-NO₂ system,changing the pressure,when the pressure was changed,the average corrosion rate and the local corrosion rate increased approximately linearly as the pressure increased.However,when the temperature was changed,the average corrosion rate increased with increasing temperature at first.While,when the temperature reached the critical point,the corrosion rate changed slowly with temperature.The local corrosion rate showd the trend of increasing first and then decreasing,and peaking at 35°C.