The failure of a boiler operating at 540℃ and 9.4 MPa was investigated by evaluation of material removed from the near-failure region and by thermodynamic analysis. A scanning Auger microprobe, scanning electron microscope, and THERMO-CALC thermodynamic software (Thermo-Calc Software, Stockholm) were used in the investigation. Results showed that the segregation of impurity elements (phosphorous, tin, and nitrogen) to grain boundaries and the in-service formation of thin carbide films and granular carbides (Cr,Fe){sub}23C{sub}6 on the grain boundaries were important factors in the failure process.
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