Crevice Corrosion Study on Alloy 22 by Electrochemical Noise Technique

摘要

Ni-Cr-Mo alloys show a remarkable corrosion resistance in a wide variety of environments. These alloys are candidate materials for the corrosion resistant engineered barriers of nuclear repositories. Ni-Cr-Mo alloys are susceptible to crevice corrosion in aggressive conditions, such as high concentrations of chlorides, low pH and high temperatures. The aim of this study was to evaluate the application of electrochemical noise technique to the study of crevice corrosion of alloy 22. Potential and current noise records were obtained from alloy 22 samples with and without crevice formers in several corrosive environments. The obtained records were analyzed in the time domain, and through statistical parameters. The objective of this analysis was to obtain confident parameters to detect crevice corrosion. Noise records obtained from tests where crevice corrosion occurred showed a clear drop in potential along with an increase of current. On the contrary, in the cases where there was no crevice corrosion, only a gradual increase in the potential is observed in the noise potential records. Analyses over statistical parameters of the records show that the current noise standard deviation is sensitive to the corrosiveness of the environment (temperature and solution composition) and to the occurrence of crevice corrosion. The results indicate that, within electrochemical noise technique, the voltage drop and the simultaneous increase in the current record are the most important parameters for monitoring crevice corrosion of alloy 22. The analysis of the standard deviation of the current records may complement these measurements.