Hydrogen assisted oxidation behavior of alloy 600 in high temperature air environment by in-situ H charging method

The primary water of a pressurized water reactor contains a higher amount of dissolved hydrogen than secondary water. Thus, it is likely that the hydrogen will penetrate the tube from the primary to the secondary side during the operation. The current study investigated the elemental distribution in the oxide film of alloy 600 during hydrogen penetration under air oxidation at 800 °C. Inward oxidation was suppressed by outward diffusing H. At the same time, the structure of the oxide film was modified. Based on the different nonstoichiometric properties of the Fe, Ni, and Cr oxide lattice, it is inferred that the outward transport of Fe accelerated significantly. At the same time, a highly mixed Fe- and Ni-enriched layer was induced by the H. Both Ar-/H-charged specimens showed the binary structure of a mixture of chromia island and pure Ni region in the inward oxide film. Oxidation along the grain boundary was also suppressed by outward diffusing H, which may explain the compositional difference compared with pure Ni specimen.