Prediction of electrochemical processess of local dissolution of stainless steels. part1 . spectral frequency analysis of potential fluctuations

The propagation of localized corrosion of stainless steels was investigated by spectral frequency analysis (HPA) of potential fluctuations in the modes of stationary and cyclic galvanostatic polarization. Corrosion-resistant austenitic and austenitic-ferritic chromium-nickel steels were studied: 12X18N10T, 10X17N13M2T, 08X22N6T, resistant to pitting corrosion, in an aqueous solution of 0.1 M NaCl with a cyanide-containing complexing agent, a corrosion stimulator -0.01 g/l (K-3[Fe(CN)(6)]). The studies were carried out in the range of low densities (0.5-10 mu A /cm(2)) due to the small values of the limiting diffusion current density in oxygen. To find the time of the origin of macropittings, it is proposed to use the NAV of chronopotentiograms with their subsequent statistical processing (Fourier transform). It has been established that fluctuations in the boundary polarization regime are characteristic of the process of the origin, development and passivation of macropittings. In the mode of stationary galvanostatic polarization, frequency characteristics were studied in the range of 1.0 +/- 0.5 mu A/cm(2). When analyzing spectral density graphs, it was found that the dominant frequency characterizes the time of formation of the macropitting, and the sections of the chronopotentiogram should be divided into sections with a duration of no more than 50-100 s.In non-stationary conditions of galvanostatic polarization in the range of 1.0-10 mu A/cm(2 )in a cyclic mode, it was found that the processes of nucleation and passivation of macropittings can be traced with a changing value of the polarizing current. Based on the frequency range of chronopotentiograms, it was found that the average macropitting lifetime is 250-300 s (frequency range 0.033 -0.004 Hz). The dominant frequencies are determined to identify the characteristic dependencies of the envelopes along the upper (f(hg)) and lower (f(hg)) boundaries of the potential change, based on them, an algorithm is proposed for selecting the values of the parameters of the prediction mode of the formation of macropitting processes.