Corrosion of 9Cr Steel in CO2 at Intermediate Temperature III: Modelling and Simulation of Void-induced Duplex Oxide Growth

Abstract

9Cr-1Mo steel forms in CO 2 at 550°C a duplex oxide layer containing an outer magnetite scale and an inner Fe-Cr rich spinel scale. The inner spinel oxide layer is formed according to a void-induced oxidation mechanism. The kinetics of the total oxide growth is simulated from the proposed oxidation model. It is found that the rate limiting step of the total oxide growth is iron diffusion through high diffusion paths such as oxide grain boundaries in the inner Fe-Cr rich spinel oxide layer. In the proposed oxidation model, a network of nanometric high diffusion paths through the oxide layer allows the very fast supply of CO 2 inside pores formed at the oxide/metal interface. Its existence is demonstrated to be physically realistic and allows explaining several observed physical features evolving in the oxide layer with time.

Corrosion of 9Cr Steel in CO2 at Intermediate Temperature I: Mechanism of Void-Induced Duplex Oxide Formation

“…This assumption will be used in the simulation of the oxide growth presented in the third paper of this work [16]. The good agreement between the simulated and the experimental kinetics consolidates it.…”

“…From a detailed study of the carbon content and its evolution over time, a mechanism of carburization, in good agreement with the proposed void-induced duplex oxide layer formation, is suggested. Finally, in the third paper (part III), a kinetic simulation of the oxide growth derived from the void-induced duplex oxide layer formation proposed in this paper is carried out with appropriate assumptions [16].…”

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

“…The diffusion coefficient of Fe in Fe-Cr spinel oxide layer can be expressed by the following relation [13]: [18].…”

Corrosion resistance of PM2000 ODS steel in high temperature supercritical carbon dioxide

“…Rouillard et al studied the corrosion behavior of T91 martensitic ferritic steel and 316L, 253MA, and alloy 800H under SC‐CO 2 at 550 °C and 25 MPa for up to 310 h. Chemical analysis in this study showed the outer oxide layer to be Fe 3 O 4 and that the inner layer was a Fe 2.3 Cr 0.67 O 4 spinel oxide layer. It has been suggested that the duplex oxide scale grows by a void induced mechanism such that the inner scale forms inside the voids created by the condensation of the iron vacancies at the oxide/metal interface . In another study , the mechanism of carburization is discussed and a Boudouard reaction (2CO = CO 2 + C) at the oxide/metal interface is suggested as the main mechanism of carburization.…”