In-situ investigation of the initial stages of KCl-induced corrosion of a chromia-forming steel at 450ºC using an environmental scanning electron microscope

Abstract

In the present work, the initial stages of KCl-induced high temperature corrosion of a chromia-forming alloy (42Fe25Ni22CrWCuNbN), Sanicro 25, is investigated by means of in-situ Environmental Scanning Electron Microscope (ESEM) exposures in an O 2 /H 2 O gaseous environment up to 1 hour at 450°C. Prior to the exposures, KCl particles were sprayed on the samples. In order to perform reliable in-situ ESEM exposures, temperature calibration of the ESEM hot stage was done. Additionally, the in-situ results were validated by reference tube furnace exposures, and the feasibility of the ESEM technique for obtaining dynamic information regarding the chlorine-induced corrosion process of the steel was discussed. Relatively large oxide crusts, with sizes of several microns, formed in the vicinity of the KCl particles. In-between the KCl particles, a thin double oxide scale (20-100 nm), consisting of a top layer rich in iron oxide and a bottom layer rich in chromia, developed all over the surface of the alloy. Metal chloride was present beneath the thin base oxide, at the alloy/oxide interface, which shows the corrosive nature of KCl towards alloy Sanicro 25 in the studied environment. However, no extensive corrosion occurred at these locations after the short exposure times used in this work (1 h).

Investigation of ash deposition dynamic process in an industrial biomass CFB boiler burning high alkali and chlorine fuel

“…5 The K and Cl contents will be released to the gas phase during combustion, which causes severe deposition and corrosion problems on the heat transfer surface of boilers. [6][7][8][9][10][11][12] The released forms of the K compounds are mainly KCl, KOH and K 2 SO 4 , and the forms tend to depend on the combustion temperature and S, Cl and water vapor content. Elemental K and Cl in the biomass are released into the gas phase as KCl when the temperature exceeds 700 C. 7,[13][14][15][16] The dissociation of K 2 CO 3 in biomass above 700-800 C will release KOH or atomic K, which is enhanced signicantly by a high water vapour content in the gas phase.…”