Corrosion characteristics and mechanisms of typical Ni-based corrosion-resistant alloys in sub- and supercritical water

Abstract

The harsh work environments caused by high-temperature, high-pressure water, especially the presence of aggressive species such as oxygen and salts, makes equipment corrosion to be a key problem restricting large-scale industrial application of the supercritical water technologies. In this work, the corrosion characteristics of Ni-Fe-Cr and Ni-Fe-Cr-Mo-Cu corrosion-resistant alloys, such as the corrosion rate, the structure and composition of oxide film, and the effects of various surface treatment processes, are discussed in detail. The corrosion mechanisms of typical Ni-based alloys in supercritical water are analyzed. Inconel 625 and Hastelloy C-276 possess good corrosion resistance over a wide range of test environments, in terms of current investigation data regarding Ni-based alloys. The outer layer is formed by a metal passive dissolution-oxide precipitation mechanism, and the precipitated metal ions are released from the barrier layer. The looseness and discontinuity of the outer oxide layer can be attributed to the decomposition of oxides in the layer, the scouring of external fluids, or growth via electro-crystallization. This information is valuable for theoretically guiding material selection and design and operating parameter optimization of key equipment in the supercritical water technologies.