Storage tank ?pressure dome? - just curious

[KiwiTanks]

Does anyone here understand what the 'dome thingy' is on top of some of the storage tanks (seen in Canada by another enthusist)

I assume it is some sort of pressure retaining apparatus, but not sure how this works.
Also I feel this tank has probably been converted to have an Internal Floating Roof (IFR) due to the 'eyebrow' vents.

 

[LittleInch]

That's unusual.

Can only think this is a tank within a tank, maybe LNG? Pity the photo obscures the letters on the tank.

Those vents might be roof drains?

Happy to be proven wrong.

 

[HTURKAK]

Does anyone here understand what the 'dome thingy' is on top of some of the storage tanks (seen in Canada by another enthusist)

Can you ask to another enthusist for more pictures specially from the backside?
I guess the dome is not on the tank but another vessel which the picture implies dome on the tank. The letters NG implies LNG.

 

[Geoff13]

The logo is Irving Oil, a Canadian oil company.

10 Riverside Dr · 10 Riverside Dr, Charlottetown, PE C1A 9R9, Canada

10 Riverside Dr, Charlottetown, PE C1A 9R9, Canada

www.google.com

In Google Streetview I can zoom in on the tank and see it's labelled "Regular Gasoline".

I believe this is a vapour dome tank. There is a flexible hemispherical membrane inside the dome. The space above the membrane is open to the atmosphere so the vapour pressure doesn't have to inflate the membrane, but merely lift it. As the temperature varies during the day / night the vapour can expand / contract without venting. In 35+ years I never designed one so I'm doing a little guessing.

The obvious problem with my explanation is the shell vents. They couldn't be there for a vapour dome to work. Perhaps there was a change of service and it's now an internal floater with Annex H shell vents? More guessing.

 

[LittleInch]

I really don't know.

Google Earth shows it has been like that since at least 2003, but the purpose is very unclear to me as the tank and roof will withstand very little pressure.

 

[IFRs]

It is ecactly as Geoff13 wrote. Before the circulation vents were added, it was a closed tank with a dome shaped membrane attached to the fixed roof where the dome attaches. The shell vents converted it to a freely vented tank, the membrane removed but the dome left there for cost reasons.

 

[LittleInch]

IFRs,

I deeply respect your knowledge of these things, but I'm just not following this one. Got any drawings / sketch of this thing as I can't find anything that looks like this.

The roof is virtually flat and it seems to store regular gasoline - why would anyone want to remove a membrane?

This is some sort of weird blob of a thing in the centre with some odd looking bits hanging off it.