5 Corrosion

General corrosion of materials in supercritical water has been the subject of large number of studies, and data now exist for at least 100 alloys under a range of conditions. This chapter introduces the key variables that affect corrosion in supercritical water (SCW): alloy composition, temperature, exposure time, water chemistry (e.g., pH and dissolved oxygen concentration), pressure/density, surface finish and grain size, flow, heat transfer. Data obtained at pressures both below (superheated steam) and above the critical pressure are presented, recognizing the underlying mechanisms at work under these two conditions are identical. The focus is on ferritic-martensitic and austenitic stainless steels, and to a lesser extent, nickel-based alloys. The chapter concludes with a discussion of approaches to corrosion modelling in SCW.