Composition, Structure, and Properties of Corrosion Layers on Ferritic and Austenitic Steels in Ultrasupercritical Water

Abstract

In situ electrical and electrochemical measurements during oxidation of ferritic steel P91 and austenitic steel AISI 316L͑NG͒, as well as of their main constituents ͑Fe, Cr, and Ni͒ in ultrasupercritical water ͑500-700°C, 30 MPa͒ have been reproducibly performed. Features observed in those measurements were substantiated by ex situ results on the thickness, composition, and morphology of the formed oxide layers from weight gain measurements, scanning electron microscopic observations, and in-depth glow-discharge optical emission spectroscopic analyses of corrosion layers. The oxidation process was followed in situ by using the contact electric resistance and contact electric impedance techniques. Impedance spectra of the Ni-Ni and Cr-Cr contacts during oxidation have been reproducibly measured. They could be quantitatively interpreted by using general considerations of the corrosion process and the mixed-conduction model for oxide films. Preliminary estimates of the diffusion coefficients of principal ionic and electronic current carriers have been obtained and their relevance with respect to available data on Ni and Cr oxidation is discussed.

Estimation of Oxidation Kinetics and Oxide Scale Void Position of Ferritic-Martensitic Steels in Supercritical Water

“…In situ electrical and electrochemical measurements during oxidation of ferritic steel P91 and austenitic steel AISI 316L (NG) in ultrasupercritical water (500-700 ∘ C, 30 MPa) have been carried out. The surface and in-depth composition and structure of the oxides formed on ferritic and austenitic steels in ultrasupercritical water are broadly analogous to those obtained by wet air oxidation in the same temperature range [6]. Angell et al [7] studied the effect of pressure on the steam oxidation of 9Cr-1Mo steels at 500-600 ∘ C and the 2 Advances in Materials Science and Engineering oxidation of the steels followed a parabolic kinetics with the oxide scale thickness increasing with the increasing pressure.…”

“…(iii) The relative error of oxide weight gain between simulation and experiments of HCM12A at 400 ∘ C and 500 ∘ C is above 40%, and the reason is that magnetite/supercritical water oxygen partial pressure is not the equilibrium oxygen partial pressure of reaction (6) or probably the error of diffusion coefficient when it extrapolated from high temperature to low temperature according to Töpfer et al 's data [18].…”

New insights into the oxidation mechanisms of a Ferritic-Martensitic steel in high-temperature steam

“…To reduce carbon emissions, it is desirable to improve the efficiency of the steam-generating power plants by increasing the operating steam temperature and pressure, such as in the ultra-supercritical coal-fired power plants [7,8] and supercritical water-cooled nuclear reactors [9][10][11]. With the increase of operating temperatures (>600 ºC), the growth of oxide film on the F-M steels is significantly enhanced [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The consequences of the thickening and failure of the surface oxides are of increasing concern in these steam-generating power plants.…”

Microstructural understanding of the oxidation of an austenitic stainless steel in high-temperature steam through advanced characterization

“…To achieve greater thermal efficiencies and reduce emissions, the advanced energy generating systems, such as supercritical water reactors and ultra-supercritical fossil fuel power-generating units, are designed to operate at ever higher temperatures (>600ºC). However, in service of temperatures above 600ºC, the high Cr F-M steels are reported to suffer severe corrosion issues [6][7][8][9][10][11][12]. Thickening and failure of surface oxides are of increasing concern in a variety of energy production plants.…”

“…For example, the progressive reduction of heat transfer by thickening oxides can lead to over-heating and failure, and exfoliation of these oxides can result in blocking of tubes or, if the oxide fragments are transported in the steam, erosion of the steam turbine [2]. Despite the high-temperature corrosion of F-M steels has been extensively studied [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], effective remedy solutions have not be developed, especially in the environments containing water vapour, which significantly limits the application of the F-M steels in the high-temperature aqueous environments.…”