Failure analysis of a fluidisation nozzle in biomass boiler and the long-term high temperatures oxidation behaviour of 304 stainless steel

The long-term oxidation behaviours are distinct from the short-term oxidation behaviours. XRD analysis indicates that the scale was mainly Fe+ 2Cr2O4 and (Fe0.6 Cr0.4)2O3. ESEM/EDS analysis indicates internal oxidation and sulfidation along the grain boundaries. The different diffusion rates of the Fe, Cr and Ni atoms formed a Ni-rich (48%) layer underneath the scale, and a Cr-rich (35%) core in the remained SS. A schematic is proposed to describe the diffusion mechanism of the internal oxidization and sulfidation behaviour.