Stress corrosion cracking of stainless steel in 300°C water: detection by EC noise and load transients

摘要

Stress corrosion cracking (SCC) is among the most common reason for components failure in the light-water nuclear reactor cooling loop. As such it is desirable to detect SCC process in component already in the early stage and preferably in-situ. One of the techniques with such potential is electrochemical noise. In the present study a duplex stainless steel with high Si content was investigated for the SCC occurrence. The environment was pure liquid water at 300 °C with 2 ppm of Li and 1000 ppm of B - an electrolyte typical for pressurized water reactor. Tapered cylindrical samples were slowly strained at various constant strain rates (strain rates of 10~(-6)/s, 5×10~(-7) /s and 10~(-7) Is) in an autoclave. During straining the electrochemical potential noise and electrochemical current noise was monitored. The load signal from the load cell was also monitored. After the experiment (peak load achieved or sample fractured) the sample was further examined by SEM. Results, which will be presented, show that transients, typical for SCC, were found in EC noise signal soon after the deformation entered the plastic regime. Moreover, also the load signal was found to exhibit characteristic rapid drops that coincide with EC noise SCC transients. The nature of both transients will be presented along with their correlation and statistics. An attempt will be made to correlate these transients with the SCC cracks observed on sample's surface.