Effects of Hydrogen Peroxide on Corrosion of Stainless Steel, (I): Improved Control of Hydrogen Peroxide Remaining in a High Temperature High Pressure Hydrogen Peroxide Loop

In order to evaluate the effects of hydrogen peroxide (H2O2) on intergranular stress corrosion cracking, a high temperature high pressure water loop, which can control H2O2 concentration with minimal oxygen (O2) co-existence, is required. This loop is characterized by (1) A once-through type loop to prevent accumulation of decomposed O2 in the loop, (2) Minimized autoclave volume to prevent bulk thermal decomposition of H2O2, (3) A polytetrafluoroethylene (PTFE) lining to prevent surface decomposition of H2O2, and (4) A H2O2 monitoring system with an off-line H2O2 detector to determine concentration in the sampled water which is combined with an in-line dissolved O2 detector to determine the decomposed O2 concentration. The authors developed such a loop previously. In the present work, performance tests were carried out and measured data were evaluated by comparing with predicted values to verify whether the target characteristics were met. The measured H2O2 remaining in the sampled water agreed with the predicted amount within 5%. It was confirmed that the ratio of H2O2 remaining in the loop autoclave was more than 90% and the concentration could be monitored continuously with the in-line dissolved O2 detector installed after the cooler in the loop. Electrochemical corrosion potential (ECP) and frequency dependent complex impedance were measured successfully by changing H2O2 concentration.