Failure Analysis of a Cracked Hydrogen Reformer Tube

The paper presents analysis of failure in a reformer tube used for hydrogen generation in a petro-chemical industry. The tube, which was manufactured by centrifugal casting of Nb-modified 25Cr35Ni alloy, developed a longitudinal crack of 200 mm length after 61,500 h of service against a design life of 100,000 h. Microstructural studies on the damaged tube material revealed presence of innumerable number of small planar cracks aligned parallel to the main crack. The damages in the material include formation of voids and cracks around the carbide particles at inter-dendritic regions. The microstructural changes observed in the tube material are typical of creep damage in 25Cr35Ni alloy. Study revealed that coalescence of voids led to the formation of small cracks and these cracks grew predominantly in radial directions in the bulk of the tube-wall. Some of the localized cracks joined to form a major crack in the longitudinal direction of the tube. Through microstructural studies, it was established that the failure in the reformer tube occurred due to exposure to temperatures higher than the safe operating temperature for a prolonged period of time.