High Temperature Isothermal Oxidation Behavior of Superheater Materials

Abstract

Abstract During combustion of biomass, alkali chloride-rich ash deposits condense on the surface of superheater tubes, thereby induce corrosion. A well-developed protective oxide layer formed from pre-oxidation treatment is an environmental friendly and cost effective technique for corrosion protection of superheater materials at high temperature in alkali salt environment. The ability of the pre-oxidized layer to protect the alloys depend on the properties such as porosity, thickness, continuity and composition of the layer. The characteristics of the oxide layer could be controlled by proper understanding on the oxidation behaviour of the materials. The main objective of this work is to obtain information on the oxidation behaviour of Hastelloy C22 (C22) and 304 Stainless Steel (304SS) at high temperature environment, hence to justify the suitability of these alloys to be subjected for pre-oxidation treatment. Oxidation of C22 and 304SS was conducted at temperature 900 °C and 1000 °C for 24 hours by thermogravimetric analysis (TGA). The oxide morphology and elemental analysis were characterized using Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The phases of the oxidation products were determined using X-ray diffraction analysis (XRD). The weight change of 304SS is higher as compared to C22 which indicates higher oxidation rate for 304SS. However, the oxide layer formed on Hastelloy C22 is more protective compared to the oxidation products of 304SS. The finding justifies the high potential of C22 alloy to be subjected for pre-oxidation treatment before used as superheater materials for biomass industry.