Electrochemical noise studies on the effect of nitrogen on the pitting corrosion of stainless steel using wavelet analysis

The effect of nitrogen on the pitting process is investigated using the electrochemical noise (EN) approach in 0.01 M FeCl3 for 24 h at a sampling frequency of 1 Hz. The EN signals were investigated using wavelet analysis on four alloys of 316L SS containing varying quantities of nitrogen (0.07, 0.12, 0.14 and 0.22 wt-% nitrogen). Using an energy distribution (ED) and standard deviation of partial signal (SDPS) plot, the primary corrosion process in various nitrogen-containing 316L SS was found. The ED plot showed that as the nitrogen percentage in the alloy increased, the energy of the low-frequency signal decreased, indicating that long-time transients were suppressed. The SDPS figure revealed a drop in pit density as nitrogen levels increased. For specimens containing 0.07, 0.11, 0.14 and 0.22 wt-% nitrogen, the pit density was determined to be 439 +/- 8, 383 +/- 6, 212 +/- 6 and 108 +/- 4 pits mm(-2), respectively.