it's always an issue of cost isn't it? Cone roofs may be more economical up to about 30 ft in diameter. After that you may see a cost benefit for using a dome. This is a very simplistic answer, but its a reasonable starting point.
I would like to get answer to be Technically rather than commercially. Please point out what is the selection criteria for Cone Roof and Dome Roof for a tank size of Dia 30' and Height 24' and this tank is for SO2 solution. We have selected API-620 and the vapour pressure is 1 psig. Please clarify about the roof.
hibruce, I'm not aware that there IS a technical reason to choose one over the other. For that matter, various other head shapes would be perfectly acceptable from a technical standpoint. There are practical differences, though.
A cone roof is simpler to layout and to fabricate. It may involve slightly more weight, but is still usually lower cost. (For a pressurized tank, the additional weight is a good thing). It generally makes the layout of roof accessories easier. For low pressures and small sizes, a cone roof will be less steep than the edge of a dome roof.
A true dome roof requires plates to be pressed. So anyone quoting the tank who doesn't normally do press work is forced to buy the roof from outside sources. And the people that normally press plates are usually not very competitive in small-size tanks (much capability = much overhead.)
The roof could be built as an umbrella. I seem to recall that API has some conflicting interpretations about the acceptability of an umbrella for pressure use, though.
If you're the owner or a consultant specifying the design, I'd recommend that you leave the choice of roof shape to the contractors.
