Acoustic emission monitoring of a Bellows and Wye section on a fluidized catalytic cracking unit

During the 1982 turnaround on the FCCU a crack was discovered in the upper bellows of the regenerated catalyst expansion joint. This crack was discovered after the third inspection inside and out on approximately the 28th day of a scheduled 35 day shutdown. This discovery required the entire expansion joint to be removed and replaced with a spare joint. This replacement prolonged the shutdown approximately 2 days, costing the refinery several thousand dollars. The bellows failure, from best information, was caused by intergranular stress corrosion cracking (IGSCC) due to chloride formation from steam purging of the bellows. This problem has surfaced in several refineries that use the same process design and expansion joint with Incoloy 800H bellows material in conjunction with a steam purge. However, the expansion joint was not the only problem encountered in this system. The ''WYE Section'' was and continues to be a major problem. Tremendous stresses are produced in this area by fatigue and differential expansion/contraction loading associated with the mechanical and operational design of the system. Cracks have been found in this area on every shutdown.