Pitting corrosion behaviour of 316L stainless steel in chloride solution with acetic acid and CO2

Electrochemical impedance spectroscopy and potentiodynamic polarisation measurements were used to verify the effects of temperature and acetic acid (HAc) on the anodic and cathodic reactions in CO2 corrosion of 316L stainless steel in 3.5% NaCl solution. The tests were carried at 30, 60 and 90 degrees C. The initiation concentration of HAc was varied between 0 and 3000 ppm. After the potentiodynamic polarisation measurements, the surface morphologies for every condition were detected by using scanning electron microscopy. In the present work, the fitting parameters of polarisation curves, such as the corrosion potential E-corr, the corrosion current density I-corr and Tafel shopes (b(a) and b(c)), were mainly discussed. In addition, the equivalent circuit was used to fit each Nyquist plot in order to obtain the important parameters. In the last section, the probable pitting corrosion mechanisms of pit initiation and growth were also analysed and validated. The results indicated that temperature and the addition of HAc have an important synergistic effect on the pitting corrosion behaviour and mechanism, leading to the increased corrosion rate with temperature and HAc.