A Fluid Catalytic Cracking (FCC) reactor in service at a petroleum refinery perforated in 1998 while operating under steady-state conditions. While the perforation was confined to a small area, a fire resulted from the release of hydrocarbons. Inspection of the reactor after the fire revealed a noticeable bulge over an extensive area near the top of the reactor shell. Local melting of the shell, resulting from the unintentional burning of
coke deposit within the vessel, was determined to be the root cause of perforation. The internal burning resulted from the local buildup of coke between the shell I.D. surface and an adjacent cyclone, and the introduction of air from a nearby purge orifice associated with an instrument tap. Bulging took place due to the loss of strength as local
temperatures reached the melting point of the metal and high thermal strains and thermal expansion due to the temperature excursion. Metallurgical changes associated with the event included microstructural transformation products, carburization and graphitization of the shell, and incipient melting of the shell at areas of prior graphitization. Creep damage to the microstructure that would have indicated that the reactor was unfit for continued service was not observed. The reactor was returned to service after the bulged section was replaced, all coke buildup removed, and the cyclone and refractory repaired.
Keywords: FCC reactor, perforation, incipient melting, carburization, graphitization, coke buildup, high-temperature equipment, fire damage