On the Degradation Modes of Various Steel Grades Used in Heat Recovery Systems: An Application from the Petrochemical Industry

Various steel grades used in the piping system of a waste heat recovery system at a petrochemical plant producing hydrogen by the steam–methane process are shown to be degraded by different modes. Pipes made of low-alloy steel (grade C-1/2Mo) have developed two problems: (1) pitting and formation of a blackish powdery deposit at the internal surface of the pipe adjacent to the inlet of the reboiler, and (2) an oxide at the internal surface of the bypass pipe fitted into a 304 stainless steel pipe. Furthermore, a welded elbow made of 304 stainless steel has developed a crack in the weld seam by a fatigue mechanism. Although the results suggest that metal dusting may be related to leakage of the reformed carbonaceous gas into the piping system, a steel resistant to metal dusting with a composition defined by %Cr + 2%Si > 24 wt% may be considered for the application. On the other hand, a steel with better fatigue resistance such as one with a tempered martensitic structure may be considered as a replacement for the 304 stainless steel.