High temperature oxidation of 9–12% Cr ferritic/martensitic steels under dual-environment conditions

Abstract

In normal operations, the opposite surfaces of the power plant components are exposed to two different environments, i.e. air/flue gas on the one side and steam on the other side. Exposure under such dual-environment can lead to accelerated corrosion of the components on the air side. The oxidation behaviour of ferritic/martensitic steel T92 was investigated under dual-environment in a specially designed test equipment. The samples were exposed to dry oxyfuel flue gas (CO 2-27%N 2-2%O 2-1%SO 2) on one side and to steam on the other side up to 1000 h at 650°C. The formation of oxide scales was characterised by optical microscopy and scanning electron microscopy with attached energy-dispersive spectroscopy. Oxidation rate of specimens under dual-environment condition was almost three times higher than that in single-environment condition. This is explained based on hydrogen transport through the bulk alloy from the steam side to the flue gas side.

Internal Oxidation of a Fe–Cr Binary Alloy at 700–900 °C: The Role of Hydrogen and Water Vapor

“…The dual atmosphere gained widespread attention in the context of SOFC almost two decades ago [10] and has been extensively explored ever since [11][12][13][14][15][16][17]. Although many mechanistical aspects of the dual atmosphere effect are not completely understood, a number of firm experimental facts were established: (i) hydrogen from the fuel side dissolves in the steel, migrates to the air side and disrupts protective scaling of Cr 2 O 3 [13,17]; (ii) the dual atmosphere effect diminishes with increasing temperature being most intense at 600 °C [14]; (iii) Cr evaporation on the air side may additionally undermine the protectiveness; however, it is not the primary reason of the effect occurring also on the dry air side [14]; (iv) cold-work [51][52][53] such as, e.g., grinding of the air side suppresses the dual atmosphere effect.…”

“…Work by Yang et al [10] showed that oxidation under such dual atmosphere conditions differs from oxidation in single atmosphere, i.e., the same atmosphere on both sides. This finding spurred a lot of work on this field resulting in somewhat contradictory results [11][12][13][14][15][16][17]. Nevertheless, it is nowadays firmly established that the dual atmosphere effect is real and recent work by Gunduz et al [17,18] explains how different parameters influence the effect and thus shedding light on the discrepancies reported in the literature.…”