Pourbaix diagram for HP-13Cr stainless steel in the extremely aggressive environment characterized by high temperature, high CO_2 pressure and high salinity

摘要

The Pourbaix diagram for HP-13Cr stainless steel (HP-13Cr SS) in the extremely aggressive environment with the feature of high temperature, high CO_2 pressure and high salinity was developed according to the thermodynamic data performed by the revised model of Helgeson. Moreover, the location of the potential of HP-13Cr SS and the pH value of formation water in such environment have been calibrated on the Pourbaix diagram by means of electrochemical measurements and surface analysis. The quinary Pourbaix diagram (Fe-Cr-H_2O-Cr-CO_2) can be obtained by the overlap of three ternary Pourbaix diagrams, i.e., Fe-Cr-H_2O, Fe-Cr-Cl" and Fe-Cr-CO_2 Pourbaix diagram. The results indicated that the Pourbaix diagrams in the extremely aggressive environment indentify the regions of immunity, corrosion, passivity and passivity/possible region, respectively. With the increase of temperature and CO2 pressure, the areas of immunity and passivity regions decreased, meanwhile, the areas of corrosion or corrosion/ possible passivity increased. Furthermore, the applicability of two dissolved species (10~(-6) mol/L and 10~(-8) mol/L) was discussed, and the results revealed that 10~(-6) mol/L dissolved species could be regarded to represent the actual environment.