Failure of panel coil components in a large sterilizer was investigated. A failure specimen was examined, and it was determined that the cracking was due to fatigue. This observation led to an investigation of the possibility of the failure being caused by vibration due to the rotating agitator. Bounding calculations indicated that the panels possessed natural frequencies between 8 and 100 Hz.
The forcing frequency of the six-bladed agitator was 15 Hz and vibration was therefore identified as the most likely culprit. Concurrently, finite element dynamic methods were used to established a natural frequency to account for the immersion of the panel in water, the frequency was close to 15 Hz. The two independent analyses both demonstrated the failure was induced by fatigue. Locations were provided for panel coil supports to eliminate the lower modes of vibration. O’Donnell personnel provided further guidance to assure the adequacy of welding processes and welding materials to achieve modifications that subsequently performed reliably in service.
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