API 579-1/ASME FFS-1 Fitness for Service on Ash Silo

Fitness for Service Evaluation & Recommendations

We performed a API 579 / ASME FFS-1 Fitness For Service Evaluation on an aging 40 year old ash silo.

Approximately 38-foot diameter x 64-foot tall, the ash silo acts as a de-watering bin as part of an ash handling system. Made of welded steel construction with a cylindrical open top shell and a conical bottom, it is elevated above grade on structural steel support legs to permit truck access for the removal of ash. A weir system sits on top of the silo, and an internal liner is attached to the cylindrical shell. The ash slurry enters the silo at the top, and 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 de-watering 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.

The results of the silo inspection found significant shell distortions, cracks and corrosion. Upon completion of the FFS evaluation,  we made recommendations to allow the owner to either make repairs or replace the silo.


We perform API 579/ASME FFS-1 Fitness for Service on components including vessels, piping and other process equipment.
Give us a call to discuss your engineering challenges.

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Tom O’Donnell, PE
(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, Fatigue, Elevated Temperature
Introduction to API 579 / ASME FFS-1

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