We were asked to perform an API 579-1/ASME FFS-1 Fitness For Service Evaluation of a 40 year old ash silo approximately 38-foot diameter x 64-foot tall. The silo acts as a dewatering bin as part of an ash handling system. It is of welded steel construction with a cylindrical open top shell and a conical bottom and is elevated above grade on structural steel support legs to permit truck access for the removal of ash. The top of the silo has a weir system and an internal liner that was attached to the cylindrical shell approximately 12 years ago. The ash slurry enters the silo at the top. The piping and platform at the top of the silo is supported by the silo’s cylindrical shell.
The silo is typically filled with slurry at approximately 90 ºF over a 4 day period. The dewatering process takes approximately 6 hours. The ash is then removed through the bottom of the silo. The total time for a single cycle is approximately 5 days.
On October 20, 2014, the Ash Silo was inspected and found to have significant shell distortions, cracks and corrosion.
We made recommendations to allow the owner to either make repairs or replace the silo.
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