Re-certification for Silo

[chuckoehler]

I have a customer that has recently purchased some large silos with the intent on using them to hold liquid fertilizer. These silos originally were used to hold grains. The size of these vessels are as follows: 44' wall length, 12' diameter, 3/16" wall thickness. Original material had a slight pressure within, while this material will be at atmospheric pressure. I am not sure what the pressure was. I have run ASME calculations on this vessel and I found that it is acceptable as designed, I am wondoring if it falls under API650, are there requirements for retaining angles?

 

[JStephen]

I'm not sure what you mean by retaining angles. If you mean intermediate wind girders, the tank problably wouldn't need them- at least not any more so than when it was a grain silo. If you mean some form of anchorage, it probably would require that, but no more so than when it was a grain silo. If it's an elevated structure, you need to look into the design of the structure very carefully, as the liquid is almost certainly heavier than what it was designed for. Ditto on the foundation if it's ground-supported.

Be aware, too, that there's really no way to recertify a tank to a different tank standard once it's built unless you have very complete information on it. So if you have any government regs or building codes that require API-650 construction, it will be hard to show that it meets it after the fact.

If these were built for silos, where hoop stress is minimal, there's no guarantee that they had full-penetration welding where specified by API.

 

[unclesyd]

In addition to JStephen's I would add a word of caution about the density of the material stored.
The reason I mention this that I became aware of the same type conversion where there was a catastrophic failure of the silo. Supposedly the conversion was made using water as the liquid when the density of the liquid was around 1.4.
When I looked at wreckage there apparently was a secondary condition developing where some components in the liquid were crystallizing near the bottom of the silo. The were much heavier than the liquid.

I'll echo concern about the welding during the original construction. The welding in this silo was very poor.

 

[chuckoehler]

Thank you very much for your help.