Page 355 - Failure Analysis Case Studies II

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Fig. 9. Cr distribution map of crack tip region (same location as shown in Fig. 6(b))

steel, excessive oxidation can occur in a short period if the operation temperature is higher than
1090°C [4].
In order to know whether the failed radiant tubes had been in service below or above 1000°C,
the degradation level of the microstructure due to thermal aging was assessed. In most of the cases,
the service temperature of the tube can be predicted by comparing the microstructure with that
under known service conditions. Figure 10 shows a typical microstructure of the failed tube.

IWF-
Fig. 10. Microstructure of uncracked region of the tested radiant tube.