scope:

Description of Driving Event:

The furnace involved was a procedyne high temperature fluidbed furnace with an 1850 degrees F maximum operating temperature. The furnace medium consisted of 1000 lbs of an alumina sand and was set to idle at 1200 F overnight. During the run fluidized media was found to be spewing out of the furnace and running down a wall in the furnace room. During the following investigation the alumina sand showed signs of sintering that suggests overheating conditions in the range of 2000 to 2200 F.

Cause of the overheating was found to be the main electrical contactor that had welded shut on 2 of the 3 legs allowing an uninterrupted supply of power to the furnace heater. Further investigation determined that a contributing factor to the mishap was the condition of the retort wall that contained a brittle fracture appearance and evidence of a stress failure rather than a thermal failure at meltdown.

The retort failed as a result of the increased thermal stress, due to the continued power supply from the stuck electrical contact, and the inherent mechanical defects in the retort wall that was not able to withstand the 2200 F temperature.