ROLE OF DISSOLVED HYDROGEN IN WATER IN CORROSION OF ALLOY 600 IN HIGH TEMPERATURE WATER

摘要

Characterization of the microstructure and chemical composition of oxide films formed on Alloy 600 in high temperature water with various dissolved hydrogen (DH) levels that allowed the Ni/NiO phase transition to occur were conducted. The results showed that increasing DH in water decreased the thickness of the oxide film, in conjunction with the increase of Cr- but decrease of Ni-concentrations in the oxide film. Further, it was found that the DH deteriorated the stability and protectiveness of the oxide film for values of DH up to and slightly above the Ni/NiO transition value. The DH effect was attributed to an oxidative dissolution process of Ni following the reduction of Ni in the oxide by hydrogen, which suggests the corrosion of Ni-base alloys in high temperature hydrogenated water is dominated by a synergic process of dissolution and oxidation.