Methods for Accessing Pitting Damage in Carbon Steel Exposed to Alkaline Chloride Waste Environments

Several laboratory methods for accelerated testing have been evaluated and their abilities to access pitting damage during immersion in environments that simulate high-level radioactive waste have been compared. Specifically, we examine and compare corrosion current density, open-circuit potential (OCP), metastable pitting data, and electrochemical noise (EN) data. In our work, a novel method for evaluating EN data has been analyzed. In this method, generalized extreme value (GEV) statistics is used to evaluate the distribution of current transient events greater than 10 μC. We show how the GEV cumulative distribution function from these EN events can be used to access relative pitting damage. Specifically, we demonstrate that the GEV distribution of EN events that exceed a 10-μC threshold correlates well with actual surface damage. However, EN experiments do not appear to predict future damage when compared to 3-month immersion testing. Therefore, while short-term changes in EN data may be good indicators of real-time material behavior, limited EN sample time (weeks) should not be used as an indicator of long-term performance.