Influence of reference electrode distance and hydrogen content on electrochemical potential noise during SCC in high purity,high temperature water

The potential and limits of the electrochemical noise (EN) measurement technique for the detection of stress corrosion cracking (SCC) initiation in austenitic stainless steels under simulated boiling water reactor (BWR) conditions was investigated at PSI within a small feasibility study. Because of the limited throwing power in low conductive, high purity water, it seems obvious that the distance between EN electrode and the specimen (or cracking location) plays an important role on the detectability of SCC initiation by the EN technique. This effect was evaluated by performing constant extension rate tensile tests in a simulated BWR environment (high purity water, T = 288°C, p = 9 MPa, O₂ content = 2 ppm) with simultaneous potential noise measurements versus multiple reference electrodes. These experiments confirmed that for the detection of SCC initiation by EN measurements the electrode distance is a limiting factor for the application in low conductivity electrolytes. The detection sensitivity decreases with increasing distance between the specimen surface and the reference (or counter) electrode. Furthermore, it was evaluated that the basic/background noise level is very low in highly reducing environment.