Corrosion Behavior of P92 in Supercritical Water

Abstract

The corrosion behavior of a ferritic/martensitic steel P92 exposed to supercritical water (SCW) at 500 to 600 degrees C and 25 MPa was investigated by means of gravimetry, scanning electron microscope/energy dispersive X-ray spectroscopy and X-ray diffraction. A dual-layered oxide scale, which was mainly composed of an outer magnetite layer and an inner magnetite/spinel-mixed layer, formed on P92. The initial oxide scale was rather porous, while the porosity decreased with an increase of exposure time. Oxidation rates at three different temperatures followed a parabolic law. The oxidation at 600 degrees C was so severe that cracks occurred along grain boundaries in the oxide scale. A probable corrosion mechanism for P92 exposed to SCW was proposed based on the above observations, focusing on oxide formation by oxygen absorption without any metallic dissolution.