Fireside Corrosion of Chromium- and Aluminum-Coated Ferritic–Martensitic Steels

Abstract

In modern fossil power plants, biomass is used more and more as secondary fuel in addition to coal. This leads to a significant decrease of the carbon footprint of such power plants. However, the demands on the corrosion resistance of the materials in the boilers increase because of chlorine in the atmosphere and salt-containing sulfides and chlorides. Heat-resistant ferritic–martensitic steels such as P91 are of great interest as superheater material. However, their corrosion resistance has to be improved for an application in modern fossil power plants with biomass combustion. For this purpose, chromium and aluminum diffusion coatings were developed and applied on P91 steel. The uncoated and coated material was investigated in a simulated biomass–brown coal ash with CaSO4, Na2SO4, K2SO4, KCl, and Al2O3 deposits and an atmosphere containing nitrogen with H2O, CO2, O2, SO2, and HCl. The improvement of the corrosion resistance is illustrated using metallographic methods such as electron probe micro-analysis.