The Corrosion Resistance Of Super13Cr Stainless Steel Tubing In High Cl~-Concentration Environment

An autoclave testing and SEM, EDS, XPS technologies were used to study CO2corrosion behavior of super13Cr steel tubing and the valence states of the elements of the corrosion scale at high temperature and high CO2pressure with high Cl-concentration environment. The electrochemical behavior and semiconductor properties of passive films and corrosion scale formed on the super13Cr martensite stainless steel were examined by using polarization curves, electrochemical impedance spectroscopy (EIS) and Mott-Schottky curves.The results showed that at high temperature, high CO2partial pressure and high Cl-concentration environment, with the temperature and CO2pressure increased, the average corrosion rate of super13Cr increased at first, and then tend to stability at higher temperature and high CO2partial pressure. With the Cl-concentration increased, the average corrosion rate of super13Cr increased at first then decreased. Mo and Ni existed as sulfide concentrate respectively in the surface layer of the corrosion scale, but Cr in form of oxide or hydroxide enrich on the surface layer.The corrosion scales formed at100℃,0.9MPa CO2and130℃,0.9MPa CO2had superior protection property. However, the protection property of corrosion scales formed at150℃,1.0MPa CO2and170℃,1.6MPa CO2reduced. The reason is concerned with the semiconductor properties of films. A typical n-p type semiconductor behavior was observed for the corrosion scales formed at100℃,0.9MPa CO2and130℃,0.9MPa CO2, the doping concentration increased with the temperature increasing. On the other hand, a p-type semiconductor behavior was observed for the corrosion scales formed at150℃,1.0MPa CO2and170℃,1.6MPa CO2. Nevertheless, a typical n-p-type semiconductor behavior was observed for the passive films on the surface of super13Cr. When Cl-concentration was less than110g/L, the doping concentration increased as the Cl-concentration increased. When Cl-concentration was more than110g/L, the doping concentration decreased as the Cl-concentration increased.There are phenomena of Warburg impedance and superimposed capacitive arc in the EIS of corrosion scale formed at higher temperature and CO2pressure. In addition, the radius of capacitive arc decreased with the temperature and CO2pressure increased. However, With the Cl-concentration increased, the radius of capacitive arc of passive film on Super13Cr decreased at first then increased.