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API-620 Tank

API-620 Tank

API-620 Tank

(OP)
IN API-620 Tank, when do we use Cone Roof and when do we use Dome Roof? Whta is the advantage?

RE: API-620 Tank

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.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

RE: API-620 Tank

(OP)
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.

RE: API-620 Tank

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.

RE: API-620 Tank

Technically, they are equal in that both will meet the code requirements.  That's why it's an econmic issue.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

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