Abstract
A new approach for estimating whether a present condition satisfies a critical one for initiating propagating corrosion cracks was developed. A change in potential fluctuation (potential noise) of a stressed specimen was measured in a chloride solution, with stepwise increase in temperature up to 80°C. A fully sensitized UNS30400 (type-304) stainless steel was used for the specimen. Under the employed conditions, the potential fluctuations are regarded as resulting from the initiation and repassivation of non-propagating stress corrosion cracks. The charge in each event was calculated from the amplitude of the potential fluctuation. The frequency distribution of the occurrence rate of the potential fluctuation was examined as a function of the charge. Propagating cracks occurred at a temperature of 80°C and stress levels of 341 or 440 MPa. At this temperature and these stress levels, the histograms of charge frequency had significantly higher amplitude in the range 0.25 to 2.5 μC, in comparison with conditions where propagating cracks did not appear. It is considered that this approach would be a promising method for monitoring the initiation of stress corrosion cracking at actual plants.
