Characterization of oxides on FAC susceptible small-bore carbon steel piping of a power plant

Wall thinning, oxides phase(s) identification, and oxide morphology characterization of nine high-pressure turbine extraction pipes (as-found thickness for pipes A through F) received from Comanche Peak Nuclear Power Plant (CPNPP) located at Glen Rose, Texas, were studied in this investigation. Phase identification performed using Fourier Transform Infrared Spectrophotometry (FTIR) showed that maghemite (γ-Fe2O3), magnetite (Fe3O4), and trace amounts of Lepidocrocite (γ-FeOOH) were present in the oxide layer on the inside surface of these small-bore carbon steel pipes. Scallop formation and severe pitting were observed. The scallop pattern was observed utilizing an Environmental Scanning Electron Microscope (ESEM) and is attributed to removal of the protective film in a Flow-Accelerated Corrosion (FAC) process. The most severe wall thinning was observed in the vicinity of welds.