**4. Conclusions**

The investigation conducted on the service-exposed reformer tube sample revealed the presence of voids and fissures along the interdendritic boundaries. The voids were initiated predominantly within the dendritic primary carbide network. The carbides were found precipitated along the interdendritic boundaries and also inside the grains in the service-exposed tube, while in the new tube, the carbides were precipitated along the interdendritic areas only. The carbides precipitated in the service-exposed tubes were M23C6, M7C3, and NbC. The precipitated secondary carbides were also found coalesced. The microstructural change as a result of the high-temperature exposure marginally increased the strength, while dropping the ductility. The investigation conducted on the service-exposed reformer tube indicated that the failure of the tube was due to creep embrittlement. The microstructural changes of the service-exposed reformer tube and creep embrittlement in a short duration further indicate that the reformer tube was subjected to overheating, which resulted in creep embrittlement. Adherence to the design and operational parameters is critical in mitigating the premature failure of reformer tubes.
