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Atmospheric Storage Drum Vent/Overflow

Atmospheric Storage Drum Vent/Overflow

Atmospheric Storage Drum Vent/Overflow

I have designed an atmospheric storage drum with a vent and a separate overflow line.  The client has requested that the vent and overflow lines be combined into a single nozzle.

We currently do not have an argument against this arrangement other than the cost of the engineering hours to modify P&IDs, datasheets, etc.  

Does anyone have any good reasons why combining an atmospheric vent and an overflow line into one nozzle may not be a good idea?  We will assume that the size of the nozzle and pipe(s) are adequate to handle venting and overflow.

Thanks in advance.

RE: Atmospheric Storage Drum Vent/Overflow


By "drum" I assume you mean a horizontal axis tank with dished ends.

In this particular type of tank, filling to the very top (solid)is usually acceptable.

With a cone roofed, flat bottomed API-650 tank, it is NOT permitted to fill the cone volume. Two nozzles are necessary. Furthermore, if the tank is filling above the overflow THE EFFECTIVE VENTING CAPACITY is compromised. Possible structural failure could result.

Short answer: for some tanks.....this may be acceptable



RE: Atmospheric Storage Drum Vent/Overflow

Yes, I meant a horizontal drum, not a cone roof tank.

Thanks for the input!  I'm sure as soon as we make this change, the client will request that we use separate nozzles for vent and overflow!

RE: Atmospheric Storage Drum Vent/Overflow

Did you tell them "There is no cost savings to combine the nozzles."?
That is probably the only reason they suggested it.

My two cents


RE: Atmospheric Storage Drum Vent/Overflow

On municipal water tanks, the overflow will generally have a flap valve, which makes it unsuitable for venting.

On many tanks, the vent is not a vent line, but a vent releasing to atmosphere near the vent nozzle, in which case, venting into a line would reduct the vent flow rate.

Consider if the vent/overflow line is filled with liquid, is it then possible to develope a partial vacuum in the tank?

RE: Atmospheric Storage Drum Vent/Overflow

Thanks for all the input guys.  A lot of good points.

In my case, the storage vessel is a horizontal drum that is actually rated for 50 psi and will get a code stamp, however it will be classified as an atmospheric storage drum because that's all that is required for it.  It is in 10% caustic service.  So... if the drum gets liquid full and starts to overflow, it will be able to handle the pressure.

I understand that in cone roof storage tanks, for example, the overflow and vents should be separate to prevent what JStephen is talking about.  Those tanks are not capable of handling much pressure.  In my case, it shouldn't be a problem.

Thanks again!


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