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.

Detection of stress corrosion cracking in a simulated BWR environment by combined electrochemical potential noise and direct current potential drop measurements

“…[9][10][11][12] Experiments with sharply notched compact tension specimens and U shape notched round bar specimens showed that the reversed DCPD technique can be applied together with EPN measurements in oxygenated high temperature water environment as a second independent method to detect SCC initiation. In all investigated specimens, SCC initiation could be detected at around the same time 11 a mean values of electrochemical potential noise (,EPN.)…”

“…7,8 A big challenge in the evaluation of this monitoring technique under high temperature water conditions is to find an independent SCC detection method which could be applied simultaneously to verify the few, but very promising, results of EN investigations performed earlier at PSI 7 and elsewhere. [9][10][11][12] The direct current potential drop (DCPD) method, which has been used for online crack growth measurements in compact tension [C(T)] specimens for many years, might be such an independent SCC monitoring tool. In the current paper, the most important results from combined EN [the term electrochemical potential noise (EPN) as used in this paper also includes more 'normal' measurement of electrochemical potential] and DCPD measurements are briefly summarised.…”

Detection of SCC initiation in austenitic stainless steel by electrochemical noise measurements

“…Most studies investigating the EN technique on its ability to detect SCC were performed in room temperature systems and had a rather 'spot check' character [7][8][9][10][11][12], nevertheless revealing very valuable and promising results. Only very few attempts were made to investigate this technique in hightemperature water environments [13][14][15][16][17]. Therefore a test programme has been started at the Paul Scherrer Institute (PSI) to investigate the suitability of the EN technique for the detection of SCC initiation in high-temperature water systems (simulated boiling water reactor environment) [18].…”

Evaluation of 08CH18N10T stainless steel corrosion in subcritical water by electrochemical noise analysis

“…Liu et al [17] measured EN of the coupling current between two identical steel electrodes as a function of oxygen concentration, flow rate, temperature and pressure in subcritical and supercritical environment. Much work was directed towards the assessment of susceptibility of boiling water reactor (BWR) construction materials to intergranular stress corrosion [18][19][20][21]. In one of the pioneering studies, detailed analysis of current noise pulses and their association with different stages of intergranular stress cracks was performed [18].…”

“…Manahan et al [19] applied coupling current noise analysis for the identification of crack events in sensitized type 304 stainless steel. The objective of other studies [20,21] was to detect cracking initiation in slow strain rate tensile (SSRT) tests. Experiments were performed on sensitized austenitic steels in a simulated BWR environment.…”