Prediction of carbide free layer formation in Fe-Ni Cr austentic steel process heater tube

The kinetics of carbide free layer formation in a process heater tube made of Fe-Ni-Cr austenitic steel during high temperature service exposure has been studied. An inte-grated scanning electron microscopy-energy dispersive spectroscopy-electron backscatter diffraction system was used for microstructural and compositional analysis of the investigated alloy tubes. A diffusion based model has been proposed to estimate the surface temperatures based on the widths of the respective carbide free layers. The model would be useful to predict the chromium concentration profiles at various times to prevent catastrophic failure of the material.