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 (H 2 O 2 ) on intergranular stress corrosion cracking, a high temperature high pressure water loop, which can control H 2 O 2 concentration with minimal oxygen (O 2 ) co-existence, is required. This loop is characterized by (1) A once-through type loop to prevent accumulation of decomposed O 2 in the loop, (2) Minimized autoclave volume to prevent bulk thermal decomposition of H 2 O 2 , (3) A polytetrafluoroethylene (PTFE) lining to prevent surface decomposition of H 2 O 2 , and (4) A H 2 O 2 monitoring system with an off-line H 2 O 2 detector to determine concentration in the sampled water which is combined with an in-line dissolved O 2 detector to determine the decomposed O 2 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 H 2 O 2 remaining in the sampled water agreed with the predicted amount within 5%. It was confirmed that the ratio of H 2 O 2 remaining in the loop autoclave was more than 90% and the concentration could be monitored continuously with the in-line dissolved O 2 detector installed after the cooler in the loop. Electrochemical corrosion potential (ECP) and frequency dependent complex impedance were measured successfully by changing H 2 O 2 concentration.