Electrochemical Noise Of Localized Corrosion Of N80 Steel

Corrosion electrochemical noise (ECN) is the spontaneous and stochastic fluctuations of current or potential in corrosion system. Electrochemical noise technique is simple and convenient. The equipment of electrochemical noise technique is simple. It doesn't bring extra disturbance to the corrosion system. It becomes an important technique to study corrosion, it also be used in the industrial field recently. More and more researchers were attracted by the electrochemical noise technique.Electrochemical noise of the localized corrosion of N80 steel in the NaHCO3 + NaCl solution was studied in this paper. The electrochemical features of pitting corrosion and crevice corrosion were studied by electrochemical noise technique using the experimental electrode and probe. Atomic force microscope and metallographic microscope were also used to study the surface of the electrode. Electrochemical noise analysis was another key point of ECN research. Electrochemical noise analysis was the analysis process of the ECN using mathematic and statistical tools. ECN curves comparing,time domain statistics analysis and frequency domain analysis were used in electrochemical noise analysis in this paper.Every process of the pitting corrosion of N80 steel had characterized ECN peaks. The different processes of pitting corrosion were identified clearly from these characterized peaks. The ECN peaks were dependent on the concentration of Cl~-. The magnitude and number of the fluctuations increased with the concentration of Cl~-. The characterized ECN peaks of metastable pitting can hardly be found when the concentration of Cl~- exceeded the critical value, the corrosion of N80 steel almost directly changed to the stable pitting after the passivation. After the same time of passivation, the number of metastable pitting peaks in one hour and the concentration of Cl~- had exponential function relation.Noise resistance (R_n) changed distinctly in the different processes of pitting corrosion, especially before and after the macroscopical pit appeared. R_n can be used to judge the different processes of the pitting corrosion.In the crevice corrosion, it was found that a huge fluctuation of the corrosion current appeared after crevice corrosion happened.