Effects of hydrogen peroxide on corrosion of stainless steel, (IV) determination of oxide film properties with multilateral surface analyses

Abstract

Corrosive conditions in BWRs are determined mainly by hydrogen peroxide (H2O2). Then, a high temperature, high-pressure H 2O2 water loop was fabricated to identify the effects of H2O2 on corrosion and stress corrosion cracking of stainless steel. By changing concentrations of H2O2 and O2, in situ measurements of electrochemical corrosion potential (ECP) and frequency dependent complex impedance of test specimens were carried out and then characteristics of oxide film on the specimens were determined by multilateral surface analyses, i.e., laser Raman spectroscopy and secondary ion mass spectroscopy. The following points were experimentally confirmed.(1) The hematite ratio in the oxide films of the specimens exposed to H 2O2 was expressed as a logarithmic function of [H 2O2], The hematite ratio was measurable for 8 ppm O 2, but negligibly small for 200 ppb O2.(2) H 2O2 exposure led to thicker oxide layers than O 2 exposure and Cr depletion did.(3) The oxide film thickness first increased as [H2O2] decreased from 100 to 10 ppb and then it decreased. This meant that a large dissolution rate caused a thin oxide film in spite of the large growth rate of oxide film, while a low growth rate caused a thinner oxide film at low [H2O2].