Gerald Wilks - CITGO
Refinery fluidized bed catalytic cracking units (FCCUs) convert heavy, low value hydrocarbons into higher value fuels by heating the hydrocarbon to high temperatures with catalyst. Exposing the heavy hydrocarbons to heat and catalyst causes the hydrocarbon molecules to break apart or crack producing the higher value products. The cracking process is carried out at temperatures in the 510-565°C temperature range and regeneration of the catalyst occurs in the 690-735°C temperature range. The process involves movement of catalyst between the reactor vessel and the regenerator vessel. The unit requires large diameter piping runs, and significant lengths of piping.
Expansion bellows are used in the piping systems to accommodate the movement of the piping that occurs as these units are started and shut down. Failures can occur due to fatigue, corrosion, stress corrosion cracking, creep, mechanical overloads, or metal embrittlement. This paper reviews causes of past failures and changes that can be made to expansion bellows design to prevent future failures.