Corrosion Characteristics of Typical Ni-Cr Alloys and Ni-Cr-Mo Alloys in Supercritical Water: A Review

The corrosion of supercritical water system materials under high-temperature and high-pressure conditions exists widely, which may result in the serious damage of the supercritical water reactor. Therefore, the improvement of the corrosion resistance of reactor material is important for ensuring the serviceability of the supercritical water reactor. This article provides a comprehensive and updated review on the corrosion characteristics of Ni-Cr and Ni-Cr-Mo corrosion-resistant alloys in supercritical water, such as the corrosion weight change, the structure, and the composition of oxide film. The influence of key parameters on the corrosion behavior of Ni-based alloys, and comparisons of corrosion resistance of typical Ni-based alloys in supercritical water, are also involved. In most cases, the corrosion weight change of different Ni-Cr-Mo alloys exposed to supercritical water (SCW) is reflected by weight gain, and first increases and then decreases with increasing exposure time over a wide range of time. The inner oxide layer is formed by the transport of anions, or conversely, of oxygen vacancies, while the outer layer is formed by the diffusion of cations but continuously dissolved. Furthermore, high temperature promotes alloy oxidation in SCW or enlarges oxide particles, there by increasing thermal stress and eventually inducing corrosion layer exfoliation.