EFFECTS OF HYDROGEN-PEROXIDE ON INTERGRANULAR STRESS-CORROSION CRACKING OF STAINLESS-STEEL IN HIGH-TEMPERATURE WATER, (I) - EFFECTS OF HYDROGEN-PEROXIDE ON ELECTROCHEMICAL CORROSION POTENTIAL OF STAINLESS-STEEL

In order to determine effects of hydrogen peroxide on stress corrosion cracking of structural materials in the primary cooling systems of bo iling water reactors, a high temperature high pressure water loop with controlled hydrogen peroxide concentrations and lower possible oxygen concentrations has been fabricated. Test specimens are installed in a stainless steel autoclave which has poly tetra-fluoro-ethylene (PTFE) inner liner to prevent decomposition of hydrogen peroxide on the auto clave surfaces. Hydrogen peroxide is injected into the autoclave inlet through the injection line which also has PTFE inner liner. The conce ntration of hydrogen peroxide is measured at the autoclave outlet by s ampling water via the PTFE-lined sampling line. More than 65% of the i njected hydrogen peroxide remains at the autoclave outlet at elevated temperature (288 degrees C). Electrochemical corrosion potential (ECP) of stainless steel is then measured in the autoclave while changing h ydrogen peroxide and oxygen concentrations. From these measurements it is concluded that, at the same oxidant concentration: (1) ECP of stai nless steel exposed to hydrogen peroxide is higher than that exposed t o oxygen; (2) ECP is much affected by specimen surfaces; and (3) ECP s hows a hysteresis pattern for on its concentration dependence. ECP of stainless steel with an oxidized surface formed under high hydrogen pe roxide concentration is much higher than that with a mechanically poli shed surface and it is less affected by oxidant species and their conc entrations.