The PbO concentration influence on oxides films developed on Incoloy 800 in CANDU secondary circuit conditions

Abstract

"The presence of lead compounds in CANDU secondary water circuit contributes to the degradation of nickel alloys involved in critical equipments manufacturing, e.g. steam generator. The pre-oxidated Incoloy 800 specimens (the steam generator tubes material) have been tested in autoclave, in secondary simulated water medium conditions: pH=9.5, at 5.1 MPa presssure and 2600C temperature, in solutions containing 100, 200 and 300 mg/L PbO, the exposure time for each concentration being 10, 20 and 30 days. The specimens evaluation after testing have been realised through ex-situ and in-situ methods: metalography, electrochemistry (potentiodynamic and impedance), gravimetry and scanning electron microscopy with energy dispersive spectroscopy. It is investigated the influence of different PbO concentrations on tested specimens surface morphology (grain, layer thickness, layer composition) and on the corrosion susceptibility, resulting in increased corrosion tendency and loss of protective properties of films as the PbO concentration was higher."