Use of electrochemical noise to detect stress corrosion crack initiation in simulated BWR environments

Abstract

The objective of this research was to investigate the use of electrochemical noise (EN) for detecting stress corrosion crack (SCC) initiation in boiling water reactor (BWR) environments. Initial experiments examined the response of sensitized AISI Type 304 stainless steel (SS) in slow strain-rate tensile (SSRT) tests in oxygenated, 288°C/10.4 MPa water, a laboratory simulation of the normal BWR environment. This combination of specimen condition and geometry assured abundant nucleation of intergranular cracks, with controllable propagation and arrest via changes in either loading or environment. In the latter case, addition of gaseous hydrogen was used to simulate BWR hydrogen water chemistry (HWC) and lower the specimen potential into a non-cracking region. The SSRT tests provided an ideal platform for optimizing the electrochemical cell configuration, while establishing the nature of electrochemical potential and current noise (EPN and ECN) responses to crack initiation, propagation and arrest. The standard deviation of electrochemical potential, a measure of EPN amplitude, proved to be the best indicator of SCC initiation, but the degree of correlation depended upon both the periodicity of the calculation and the electrode configuration. Further development work is expected to lead to a useful, in-plant sensor for real-time detection of SCC activity.