Annular and Bottom Plate of a Crude Storage Tank.

[Arshad Ahamed]

Hi all,
Could someone kindly clarify what the intended purpose, salient features, differences and the construction w.r.to shell plate of the Bottom and Annular Plate is?

What implications does it have on the tank design?

Also, what is the Diameter-Height ratio prescribed by the norms?

Thanks and Regards.

 

[MJCronin]

Can you restate your question ? ... I do not understand

MJCronin
Sr. Process Engineer

 

[mk3223]

Do you mean what is the annular plate? It's the piece of the bottom plate just under the tank vertical shell plate.
As for the tank D/H ratio, it can be less than 1 for the field elected tank as the adequate space is permitted, and higher than 1 for the shop fabricated tank.

 

[JStephen]

There is no one answer to the height/diameter question. If there are no other considerations, the (estimated) cheapest set of dimensions will be used. However, those dimensions will vary depending on the contractor, the foundation requirements, coating requirements, plate availability, etc. If the whole tank and foundation is a package, you can let contractors pick desired dimensions for the capacity. Note that certain H/D ratios will be better or worse for allowable bearing, wind overturn, seismic overturn, etc. Typical shell heights will be multiples of the commonly used plate widths (so, in the US, you get 24', 32', 40', etc., based on 8' wide plate).

An annular ring is normally used in cases that generate higher stress in the bottom plate, or those cases where the plate near the shell needs to be thicker than the remaining bottom. The normal (but not universal) practice is to use an annular ring only in those cases where it is required by API-650. Generally, large tanks, hot tanks, tanks in high-seismic areas.

 

[MJCronin]

JStephen gives solid advice ...There is no one answer to the height/diameter question.

If this is your first major flat bottomed tank, get help from an experienced engineer

MJCronin
Sr. Process Engineer