The Corrosion Behavior Of 13Cr And Super 13Cr Stainless Steel In CaCl₂ Completion Fluids

The purpose of this work was to clarify the effect of temperature, brine concentration, dissolved O₂, acetic acid and the strain on SCC, and the difference in corrosion electrochemical behavior between specimens with and without stress for 13Cr and super 13Cr stainless steels in completion fluids containing CO₂. The effects were investigated by using the four-point bend test, U-bend test, the surface analysis and electrochemical measurements (potentiostatic polarization, potentiodynamic polarization and electrochemistry noise).The study results for 13Cr stainless steel showed that in 33% CaCl₂ brine with no deoxidization, 13Cr stainless steel mainly suffered general corrosion and pitting corrosion both at 100℃and 150℃; however, in 33% CaCl₂ brine with deoxidization, 13Cr stainless steel mainly suffered general corrosion and cracks both at 100℃and 150℃. The adding of acetic acid could accelerate the general corrosion and the general corrosion rate increase with the enhancement of the acetic acid concentration. And the pitting corrosion was overspreaded by the adding of the acetic acid concentration in 33% CaCl₂ brine with no deoxidization, but the cracks was restrained by the adding of the acetic acid concentration in 33% CaCl₂ brine with deoxidization. The corrosion rate was also accelerated by the system temperature. The results of electrochemistry test were consistent with the exposure experiment results, and the pitting corrosion bourgeon of 13Cr stainless steel under the test condition in short time was confirmed by electrochemistry noise spectrum.The results for super 13Cr stainless steel showed that acetic acid increased the stress corrosion cracking susceptivity of super 13Cr stainless steel in 33wt% CaCl₂ brine at 150℃and 1.0MPa CO₂ under no deaerated condition, but it reduced the SCC susceptivity under deaerated condition. SEM morphology showed that SCC of super 13Cr stainless steel was intergranular cracking mode in the 33wt% CaCl₂ brine at 150℃and 1.0MPa CO₂. The passivate ability of super 13Cr stainless steel was weakened in the deaerated 33wt% CaCl₂ brine at 150℃and 1.0MPa CO₂ especially presence of acetic acid. The results of potentiostatic polarization and potentiodynamic polarization experiments demonstrated that the cracking is initiated by the anodic dissolution in the secondary active-passive transition region.