Geodesic Dome Roofs - Disadvantages / Issues during life 3

[JRJJ]

thread507-471991

I am currently looking at what the advantages and more importantly the disadvantages of using an aluminium geodesic dome roof tank in lieu of a carbon steel floating roof.
Tank >40m dia with a petroleum product.

I have searched online however there really is not a lot of specific information on the disadvantages/issues, lots of information however on the advantages, although most linked to the sales of such product.

Regards,

JRJJ

 

[LittleInch]

A geodesic roof will not take the place of a floating roof.

What it does, AFAIK, is simply take away the rain / snow load off the floating roof.

That previous post seems to provide you with a lot of points and answers.

Only you can see if the cost of an internal floating roof plus geodetic roof or external floating roof with no roof or internal roof with a steel cone roof will be the most economic.

From my limited experience, the geodesic roofs are only where you have huge amounts of rain or snow or where the EFR has failed in its drainage system or where someone wants to convert an open to tank into a FR tank. I've seen many many refineries and tank farms and can't remember a single geodesic roof which kind of tells me they are not an economic solution.

Hopefully EFR will turn up and tell me I'm right or wrong, but this is in the wrong forum - should be in the storage tank forum.

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

 

[JRJJ]

LittleInch, thank you for your response much appreciated, i probably was not clear enough in what i was asking, i was looking to see if there are any issues with having these type of roofs in operation without looking at the cost aspect.
You are also right i have posted this in the wrong area, will sort that now, thank you.

 

[JedClampett]

We use a lot of these in the wastewater treatment industry. There's been some consolidation in the aluminum dome manufacturers, so competition is a problem. We like to use them to contain odors, so we'll require a pressure test. These are hard to pass and involve a lot of caulking. But if they leak a little, it's not the end of the world. It's either a small amount of odors leaking out (in a sewage treatment plant) or rainwater leaking in (once again, into different sewage processes), so they're not critical. We've had some issues with surface corrosion on their SST hardware. It's unsightly, but not critical.

Access is a difficult issue. The contained equipment usually has a walkway, but framing the dome around a vestibule is a design challenge. And obviously, the dome is not a heavy-duty structure, so personnel either can't or don't want to get on it.

I'd say they're generally a good product. I'm not sure what other options there are for covering large round vessels.

 

[JRJJ]

JedClampett, thank you for this, very useful information, you sort of confirm my fears around the sealing of the panels, i am being told the caulking will last for upto 15years without leaking however i find that a little hard to believe that's why i am asking in this forum.

tHANKS AGAIN,

JRJJ

 

[BridgeSmith]

I'll relay an anecdote I learned while while in school at the University of Wyoming, that may be pertinent here.

The geodesic dome roof of the Arena Auditorium was designed in timber instead of steel, because the timber compression struts (which are basically all of the members in the roof) would still have enough uncharred section not collapse in a fire, but the steel would get soft and buckle due to the heat. I would expect aluminum members would have the same issues with getting soft and buckling as steel.

 

[JRJJ]

BridgeSmith, that's a very good point you make re. fire, and one i did not consider.

Thank you

JRJJ

 

[BridgeSmith]

BridgeSmith, that's a very good point you make re. fire, and one i did not consider.

As I reread the OP, I realized it's a "petroleum" tank, so I'm not sure it would matter what material you used, if the contents were to catch on fire.

If there was a fire in the tank, neither wood, steel or aluminum would survive very long. The limited char depth for timber is predicated on it being exposed to 'normal' fire temperatures. A petroleum fire would be much hotter, so the difference in the time to collapse would probably only be a few minutes.

OTOH, if I am correct in assuming the "floating roof" mentioned earlier literally floats on the liquid in the tank, that would presumably to limit the mixing of oxygen and fuel, which may quell any fire that did get started.

 

[LittleInch]

The OP isn't being forthcoming, but I think this is looking at using a geodesic roof instead of a steel cone roof with a central pillar or pillars.

The roof would need to seal so that vapours can be taken somewhere and burnt or absorbed or liquified. The vapour space is quite flammable and in the event of fire the roof just collapses.

If sealed the tank also needs to be kept under low, but positive pressure at all times to prevent the roof collapsing. This isn't always easy and can fail and the roof doesn't like flexing.

Floating roofs limit vapour loss and will generally prevent fires except around the rim where they can be extinguished with foam more easily. Or not, the roof sinks and the tank burns down....



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

 

[JRJJ]

Gents apologies I am indeed referring to a floating steel roof that would float on the product, in comparison of a geodesic dome roof.
The steel floating roof is proven in a petrochemical environment, even with fires ( so long as a sufficient foam system is in use) recently I have seen an increase in (mainly sellers) a push for geodesic roofs to replace steel floating roofs however I am sceptical they are a better long term solution and was just looking for information to either back up my thoughts or reassure me that they are indeed a viable alternative.
As the geodesic roof is new to me I really do not know what pitfalls I could encounter.
I really appreciate all your comments.

JRJJ

 

[LittleInch]

For me I think the issue is more one about the overall package and maintenence, not just the roof.

EFR tanks are essentially a fit and forget ( they do need some love) and reduce emmssion to acceptable levels for most countries.

Replacing an floating roof with a geodesic roof implies that now you need somewhere to deal with the vapour from the tank at very low pressure so a big vent line to ?? plus a very reliable blanketing / inert gas system to maintain gas pressure above atmospheric pressure otherwise the roof and tank will collapse. The vent line and vapour handling equipment requires maintnenece and are often costly to run.

EFRs have issues about leaks around the rim seals, roof drains and may be a little more expesnive than the geodesic roof, but for me are far simpler to operate and maintain.

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

 

[Gforce1]

Is it permissible to use aluminum? Aluminum construction tools/materials are banned on many petrochemical sites due to the possibility for unintentional sparks generated on contact between steel and aluminum.