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Earl   AST Forum  

Dome vs. cone Roof

Monday, December 27, 2004   By: Smit
What would be the minimum internal design pressure for an API 650 tank after which we would necessarily opt for dome roof in place of cone roof? I understand it will also depend on tank geometry but I just wanted to have a feel for the numbers. Appreciate for all the help.

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Tuesday, January 04, 2005   By: jzwack@CBI.com
Typically we see Dome Roof on Appendix F tanks. We can handle the large +/- 120' dia dome/ umbrella tank with pressed dubble curved plate without a problem. Please feel free to email me and we can discuss this in more detail. Regards John Zwack

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Monday, January 03, 2005   By: Stephen
From a contractor's standpoint, the decision would be made based on both cost AND capabilities. From an owner's or consultant's standpoint, it would probably be best to specify the pressure and shell dimensions required, and let the contractor come up with the most economical roof. It should be possible to construct a pressured umbrella roof, but one of the API interpretations specifically precludes this from the API-620 type design. That being the case, the roof will either be a cone shape or a pressed dome, and there aren't that many companies around that routinely press large segmented domes. Even if a dome shape is specified, the selection of the best dish radius would still be an economic decision, and would be best left to the tank contractor. In most cases, the design problems have more to do with the design of the compression ring rather than the roof plate itself.

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Tuesday, December 28, 2004   By: Steve Braune, Tank Industry Consultants
There may not be a single answer to the question you posed. If the decision is left to the tank manufacturer, the answer will always be driven by cost. Whichever one is cheapest (and gives the best bid price) will be selected. For smaller diameter tanks a cone will typically be cheaper... perhaps up to about 40 feet in diameter. Thererafter, I'd expect to see a dome roof. Remember, economics trump all. Are you using this info to update your computer program or is it just curiosity?

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Tuesday, December 28, 2004   By: MJCronin
Smit....See this link http://www.ast-forum.com/astforum2003/_discAST/00000451.htm ........Hope that you can get a better answer this year......MJC

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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