Hermetic roof on the tank - are there any regulations specifying whether it can be used or not? 2

[Indyvidual]

Hello,

I have a question, is there any rule in a standard such as API 650 specifying the conditions under which the use of an airtight roof on a tank (in this case for gasoline) is allowed?
Some companies use internal floating roofs + dome roofs, but I have also come across cases where the airtight fixed roof is attached to the tank with only 1 or 2 vent valves.

Where to look for the answer to such a question?

 

[HTURKAK]

The title of the thread is ( Hermetic roof on the tank -.... )

I am not sure for the reason to name hermetic but implies the isolation of content and vapor accumulated at the top. I wiil suggest you to look ,

- API 2000: Venting Atmospheric and Low-Pressure Storage Tanks

- Vapour recovery technics

- The following document at the link is useful to get the concept of nitrogen blanketing ,

http://www.airproducts.cz/~/media/downloads/article/N/en-nitrogen-blanketing-article.pdf

 

[JStephen]

In the USA, federal air standards require floating roofs for larger tanks with more volatile contents, but exempt tanks below a certain size and also exempt tanks with less volatile contents. Those standards can be found in the Code of Federal Regulations, available online. Note that different rules may apply depending on the use of the tank (crude oil vs pipeline breakout vs terminal, etc.).

 

[LittleInch]

The answer is in your data sheet and the tank design.

When you say "vents" do you mean free vents to the outside or to some sort of vapour handling?

The issue with that is the internal pressure of an API 650 tank is very small and tends to need very large piping to handle vents.

In most countries nowadays you can't discharge gasoline vapours direct to the environment. Internal floating roofs are the best method of reducing vapour emissions.

Other than a open top tank I would have assumed all roofs were sealed. Certainly wouldn't assume any venting is occurring outside of the vents.

Even a frangible roof is sealed, just "weakly".

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IFRs]

You can have a sealed API 650 tank with or without a floating roof or gas blanket for gasoline but it will need to be connected to a vapor balancing system.

 

[Indyvidual]

Thank you for all your responses.

 

[LittleInch]

So what are you going to do?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Indyvidual]

Maybe I'll change the question a bit.
If the Structurally-Supported Aluminum Dome Roof (API 650, Appendix G) was sealed and became a fixed roof of sorts, wouldn't there be durability issues with such a dome?
I wonder if, if there are no vapor control devices in the tank, whether the dome would be able to withstand this pressure (because at this point a non-pressure tank became a low-pressure tank).

How does API 650 section G.4.3 relate to this in this case (I'm sending it in an attachment)?

PS. Unfortunately at this point I don't have technical sheets for tanks and domes. I'll probably have them next week, for now I wanted to check what the standards say on this subject.

 

[LittleInch]

The section makes it quite clear what the maximum internal pressure is (lower of weight of roof or 9 inches wc).

You would need to put in vents and pressure protection to prevent pressure rising above the max internal pressure. That would need to account for any vapour emissions, max fill and empty rate, max temperature etc etc

No different to any other tank, only that the pressure from the roof might be very very low as it won't weigh a lot.

That's it, end of story. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.