Abstract
Fluid Catalytic Cracking Unit (FCCU) vapor recovery systems are known to be susceptible to corrosion and hydrogen blistering as a result of exposure to cyanides and a wet hydrogen sulfide environment. As a part of our plant inspection program, we have monitored the development of hydrogen blisters and subsequent hydrogen induced stepwise cracking in our FCCU absorber deethanizer tower over a ten year period. Inspection methods consisted of visual inspection, wet fluorescent magnetic particle and liquid penetrant testing of welds and base metal to detect cracking. Material samples were removed from areas with severe corrosion for examination and recommendations by our corporate metallurgical laboratory. The ASTM A212, Grade B carbon steel vessel was condemned due to extensive hydrogen induced stepwise cracking in the shell material. A new tower constructed of ASTM A516, Grade 70 carbon steel and overlaid with 309L stainless steel was installed. Hydrogen blistering was detected in additional FCCU recovery section vessels which were inspected using the same inspection techniques. Corrosion resistant shotcrete liners were installed in this equipment to minimize further corrosion and hydrogen blistering due to wet hydrogen sulfide attack.
