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Fitness For Service (FFS) Evaluation on an Aging Ash Silo

Image of Ash Silo for FFS

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.

See also:

API 579-1/ASME FFS-1 Fitness for Service on a Brewery Tank
API 579-1/ ASME FFS-1 Fitness for Service on Wood-Fired Boiler Components
 
Fitness For Service
(PDF) “Weld Defects and Failures: Quantifying Fitness For Service – How Finite Element Mathematical Simulations can Mitigate Risk, Cut Costs and Improve Overall Safety”
Publications – Heat Exchangers, Pressure Vessels, Welds and Other Applications, Fatigue, Elevated Temperature
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