Complete Drainage of Storage Tank

[tabiscari]

Greetings
We are designing a Fuel Oil Tank
ID= 220 ft
H= 64 ft
Roof: Structurally supported cone roof
Bottom: Apex up, 1:120 slope (center is higher than periphery)

We are having a problem with the tank drainage:
The client request the complete drain of Tank in case of maintenance: to accomplish this, we suggested 4 draw-off sumps of 6" each nozzle.

1) How close can the sumps be between them?
As drainage lines are steam traced, they cannot be underground by Project Specs, given this situation, we have considered to gather all 4 drainage lines (and sumps) as close as possible not to interfere with other shell connection between drain nozzles

2) Is it possible to put more than one pipe inside a sump?

3) Table 5-16 of API 650 establishes NPS 6" as maximum, but paragraph 5.8.7 gives an open window to the purchaser, could be installed a single drain nozzle of 12"?

Thanks

 

[JStephen]

I don't think there's any reason you couldn't use a larger drawoff line in a sump. I don't recall the wording of API-650, whether the standard sump sizes are the only ones allowed or whether other/larger sizes can be used.

 

[gr2vessels]

Clause 5.8.7 says indeed 'shall be....unless specified otherwise by the Purchaser'. That is, you may install a single drain nozzle of 12", provided all the associated engineering is done correctly.
Cheers,
gr2vessels

 

[tabiscari]

Thanks for the clarification, but I'm a little concerned about the sump dimensions and if that could affect somehow the construction of the foundation, or the settlement
I'm not too familiarized with the construction process, is the sump constructed during foundation or after foundation is done?
This I ask in order to tell Civil discipline to consider this or not and if it is in vendor's scope of supply
Thanks again for your help

 

[fegenbush]

"...is the sump constructed during foundation or after foundation is done?"

It depends on the foundation type and how you design it. For example, if you have a full slab foundation, obviously you must install the sump with the slab. There are other factors as well.

 

[tabiscari]

Greetings fegenbush
This Tank has a concrete ringwall and compacted soil

 

[gr2vessels]

The full description of sump installation is in the 'Note' of figure 5-21. However, the tank installer only need your As Built drawings, let him do the job...
Cheers,
gr2vessels