The FCC reactor at a UK refinery had been in operation for some 15 years and had exceeded its creep design life of 100,000 hours. TWI co-ordinated a site team in order to undertake a remaining life assessment. It was concluded that the reactor was currently fit for purpose with the potential for life extension.
Before an activity of this nature can be undertaken, it is essential that all potential failure modes are considered and the most likely locations are identified. In the present case, where creep rupture was the failure mode of most concern, it was necessary to undertake a stress analysis of the reactor and identify the inspection locations. The next issue is to select the most appropriate NDT techniques. In the present case it was decided to employ 'CEGB' qualified microstructure replicators, supplied by Thermal Engineering International (Wakefield), who also undertook hardness surveys. This was combined with ultrasonic thickness measurements and flaw detection, and with magnetic particle inspection (MPI).
The replicas were taken at locations of highest stress and the extent of microstructural degradation and creep cavitation was assessed by a metallurgist with over 20 years experience in interpreting such damage. The microstructural analysis was combined with the other NDT results and a full interpretative report produced.
Conclusions and Recommendations
Conclusions were drawn on the material microstructures, degree of microstructure degradation and extent of creep cavitation. An estimation of the life of the reactor components was made in terms of a percentage. Based on these results, it was possible to consider the duration of continued safe operation and to make recommendations on future inspection intervals.