Atmospheric Storage Tank nozzles / valve

[tkdhwjd]

Dear Colleagues,

For atmospheric storage tanks, I have heard that in general, all tank nozzles (except those on a roof) should have valves located at the tank nozzles. I have checked API guidelines, but was not able to find any explanation to why the valves need to be located at the tank nozzles. Is it also acceptable to install a short spool piece (if necessary for a reason) in between the valve and the tank nozzle? Understand that having additional flanges will result in higher possible leak sources, but I cannot think of any other reasons. Any comments will be greatly appreciated.

 

[ash9144]

An arrangement of a short spool on the tank nozzle then a valve is a good practice. You may even want a spool with a bleeder and another valve following the first valve. The spool on the tank allows for a break out spool which makes it easier and safer to isolate the tank for entry. The double block and bleed allows for isolation of the break out spool. But if you are just installing a valve it would need to be at the tank nozzle to allow isolation at the tank, otherwise you would have a hard time isolating the tank for entry to meet OSHA requirements

 

[gr2vessels]

tkdhwjd,
The shell side nozzles won't take much of the load, unless specifically designed and reinforced for a specified load. Any valve installed on the nozzle could exceed the limit of allowable external load. In addition, there is the pipe connected to the valve, adding to the nozzle load. So best is to avoid excessive nozzle loads and the associated cost increase by connecting first a pipe spool and then the valving arrangement as explained above. Obviously, this is valid for larger nozzles than small instrument nozzle sizes.
Cheers,
gr2vessels

 

[BenThayer]

you might look at NFPA if you have a flammable solvent.

it might be quantity related but i think there they may be a recommendation or requirement (or it may just be an in-house practice) for a fire-safe shutoff valve on the bottom of the tank for valves to pumps, etc. that would normally in the open position.

also, the fewer the flanges between the valve and the tank, the fewer places to have leaks.

 

[MJCronin]

thk....

I agree with BenThayer...

My understanding of the reason to place valves directly on storage tank nozzles is to minimize the section of piping that cannot be isolated in the event on a piping leak. If the valve is on the nozzle, there is only one possible leaking flange to worry about.

Secondly, for flammable liquids, it has been standard practice in many companies to locate a spring loaded "fail safe" valve with a fusable link on tank nozzles.

(See:

http://www.bitorq.com/fusible_overview.html

)

API-607 contains design requirements for "fire safe construction"

I do not believe that there is a specific reference to this general requirement in NFPA standards for process plants, although NFPA-37 contains mention of these valves for Fuel Oil Systems.. (but I could be wrong...)

Anyone else out there got somethin'

-MJC