Roof Structure for Dome Roof Tanks

How big is your tank?

Do you really need a perfect dome or could it be segmented to approximate the shape of the dome?

It's Tank Diameter is more than 40m.

Perfect dome.

Regards

The problem is over because it is impossible to be perfect. Even if it was fabricated to be perfect, it would sag under it's own weight to a less than perfect shape. It could be fabricated from smaller rolled plates but assembling and welding them into the perfect shape over 40m diameter is not feasible.

One chance, what is the allowable tolerance?

I think i am not able to project my question properly.You replied about Dome roof plate.My question was for the roof structure supporting Dome roof.Another question can be go for hot rolled sections readily available in market to support such dome.If is it so then what about rolling as we can roll section only along length.whether Rolling along length is sufficient for dome roof shape as a support roof tructure.

Regards

For the structure, yes single rolling would work, but understand that it is not exact. The section is bent till the extreme fibers are stretched beyond the elastic limit but the the inner fibers are not, there is an unknown amount of springback when the member is released.

You need to ask fabricators, only ones that you might use, how close each can get.

No matter how perfect you make your dome, the first day it is exposed to direct sunlight the metal will expand according to the material properties (and the equation below). As the individual plates expand they will mar your perfect dome shape.

All of the dome roof tanks I have been in have self supporting dome or cone roofs. All the pictures I have found on my hard drive were of cone roof tanks...I can't recall where exactly I have seen true dome roof tanks (except for geodesic domes over floating pan tanks)

The dome roof tanks I found googling looked to be flat plates that are cut and welded to make the dome shape, you can find drawings that show you how different geometric shapes make a dome or just work it out with the rectangles.

Drew K

Does it have to be steel? Or could you use concrete?

Only Steel is to be used.

Regards

How are silo domes made and supported? Even though much smaller, are there any ideas there? I can see support members (I or H or C sections) being rolled, then covered with a lighter metal "roof." But any covering will have to be sectional--even the much smaller silo cover is sectional.

It is quite impractical to make a perfect dome. The differential expansion mentioned above is only one reason.

Talk to these guys.

This is a picture of a geodesic dome designed as a water cover over a floating pan on an open tank.

Drew K _{(didn't click on link though)}

The next question would be "is this to be a shell structure or is it acceptable to create a grid to hold a domed "weather guard". Such a weather guard would rest upon the I beam or pipe dome, and not carry any weight itself, and need not be made of steel. Canvas or plastic would serve as well.

I think you would find it easy to find an engineer to design a domed I beam structure capable of handling any forseen load, but you will find it VERY difficult to get somebody to sign off on a shell structure made entirely of steel plate. Any ripple or distortion on a shell structure will result in catastrophic failure, and will prove very difficult to assemble. The bigger the structure, the more difficult it is to create a serviceable shell.

Once you have a grid, you can easily fabricate the panels which would mount upon it. If you want to cut sheet metal to suit a dome shape, say hex panels like a soccer ball, or comparatively short triangles like a geodesic dome, or even long 20 meter gores, they can be easily fabricated in a reasonably well equiped machine shop. I would employ an English wheel to get the compound curves if you were looking for a little bit of extra stiffness. (I work with pieces around a meter by a meter every day on MY english wheel with excellent results. Would not dream of trying it on anything much larger than that, though a 20 meter gore might be kind of fun...once.)

Guess I should have read the question more closely...seems a domed weather guard is NOT what is required here...but rather something which can withstand 14PSI over 40 meters.

Dude, 14PSI over 40 meters diameter will be able to lift the CN tower off its base!!! That'll require a seriously strong shell!!! It has to withstand fifteen hundred pounds per square meter, and you got a pressure of two hundred and nineteen thousand pounds.... basically 119 tons.

Okay, not "quite" the CN tower...but seriously, thats a pretty powerful tension you are dealing with! Perhaps the propane industry would have something like that?

Good luck with that.

Is there a reason you are going for a dome instead of a cone? With steel unsupported steel structures, the cone could more easily be made from flat triangles welded together.

The more I think about it the less confident I am in remembering what I saw when I looked up in a cone roof tank...

Drew K

Yeah it was client requirement to have Dome roof with internal pressure say as high as 14.5 PSI & is to be designed as per API 620 requirement with tank Diameter mostly greater than 38 m.Its an Aramco project.

Regards

aha...well, that would require a dome...a very well built one. A positive pressure of one atmosphere spread over a large area is a tremendous force.

I would subcontract it out to experts so you are not liable for the integrity of the tank or at least bring in some experts in the field to help design it.

Drew K

Actually, such dome plates do not need to be rolled in both directions, unless your client insists on paying MUCH more money than needed to achieve the same end result with triangular panels supported by a triangular grid.

Alternatively, take a soccer ball, and put it in a cylinder that only comes up half way to the top of the ball. Then, arrange toothpicks in a triangular pattern that only covers the top, exposed, half of the ball. Glue, or otherwise attach the ends of the toothpicks to each other, Then you can lift off the semi-hemispherical ''lid'' of toothpicks off the ball and your structural engineer(s) will get a better idea of what needs to be analysed, and how to analyse it. Then stop and think just how big a 40 m tank cover is,,,

In the mean time, talk to tank manufacturers about how they have tanks covered with dome-covers in the past, and save your self a lot of time and money by going with a proven solution from past experience applying their greater expertise.

I will repeat...... a single giant flat bottomed tank designed for 14.5 psig is a bad idea. The type of roof, cone or domed, that is selected will make no difference.

Multiple horizontal "bullet-type" tanks should be considered. (lots of propane is cheaply stored this way)

The client should state both the actual operating pressure and the design pressure range.

What is the actual liquid stored and what is the design temperature of storage ?

What is the vapor pressure of the liquid at ~120F ?