Corrosion Behavior of X65 Steel in Carbon Dioxide Solution under High Temperature and High Pressure

Corrosion characteristics of X65 steel under four different high temperatures and in NACE solution saturated with CO₂ at 1 MPa partial pressure were investigated by using autoclave,SEM,XRD,weight loss methods and electron-probe micro-analysis.The result showed that in the studied temperature ranges,X65 steel was corroded seriously by CO₂.With the temperature increasing,the corrosion rate of X65 steel had a tendency of decreasing first,then increasing,and the minimum rate appeared at the temperature of 90℃.The main corrosion scale is ferrous sulfide.The effect of CO₂ corrosion made the surface of X65 steel have a feature of point corrosion,pitting corrosion and mesa corrosion.Cl^- excited point corrosion and enriched in the pit of point corrosion,which brought the concentration of Cl^- on part surface of sample different,and accelerated the point corrosion reaction.The corrosion of CO₂ was the result of interaction of multi-factors.