Corrosion Behavior of T91 and Type AISI 403 Stainless Steel in Supercritical Water

The corrosion behaviour of a ferritic/martensitic steel T91 and a martensitic stainless steel type AISI 403 exposed to supercritical water (SCW) at 450°C and 25 MPa for up 750 h was investigated. After each exposure period, the amount of oxide formed on the samples was determined by gravimetry. The oxide morphology and composition were characterized using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). Results show that for both materials the oxide growth follows a behaviour between parabolic and cubic growth laws. The type AISI 403 stainless steel with a higher Cr content was found to have a better corrosion-resistance performance than the T91 steel. A dual-layered oxide scale, which was mainly composed of an outer magnetite layer and an inner Fe/Cr spinel layer, formed on both T91 steel and type AISI 403 SS.