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API 650 ROOF TANK DESING!

BMechanics888 (Mechanical)

(OP)

17 Apr 12 03:49

Hi to everyone!

Could someone help me? I know that there is a previous post (2003) about this issue but I am not sure if things have changed since then.

I have some doubts with reference to the roof tank design. It is not clear for me under which conditions do I have to use dome or conical roofs, and when self-supporting or structural supported roofs. Does it just depend on the diameter of the tank? The process liquid/gas has something to do here?

In case of using structural supported roof, it is possible to make a design according to frangible roof conditions?

Sorry if my questions are a little bit general, but I am starting in this business.

Thanks in advance and congrats for this Forum, I'm becoming an addict!

IFRs (Petroleum) · Answer 1 · 2012-04-17 06:08:53

API 650 does not care or specify what you fill your tank with, it gives you design guidelines for the tank and roof, etc. The choice of type of fixed roof is yours.

BMechanics888 (Mechanical) · Answer 2 · 2012-04-17 06:53:50

Thanks for your response,

But is there any criterion to follow when choosing the type of roof? Or any advantage of cone roof over domed roof?

I have been told that now the most used are the domed type.

Thanks a lot

IFRs (Petroleum) · Answer 3 · 2012-04-17 07:01:58

You can use self supporting roofs up to a certain size and load, then a rafter supported roof becomes the norm. Structurally supported roofs can indeed meet the frangibility critera set forth in API 650.

Roohol (Mechanical) · Answer 4 · 2012-04-18 01:11:05

Hi;
there is an ambiguity in the API 650 about roof types.
based on my experiences and searches i have found that up to 5 m diameter it is better to select a cone self support roof ( without any structure and just plate), 5 < D < 15-17 meter, self supporting cone roof (with rafter & girder) , 15 < D < 50 m self supporting dome roof (with rafter & girder) and D > 50 m , column supported cone roof.

I hope this answer will be helpful.

lganga (Mechanical) · Answer 5 · 2012-04-18 08:40:39

Hello

For your information, ours 650 appendix F tanks have self supporting cone roofs with a 10 mts diameter. They are in service since 1985.

Regards

BMechanics888 (Mechanical) · Answer 6 · 2012-04-18 11:29:38

Thanks to everyone for your responses.

It is much clearer for me now. Anyway I will keep looking for examples, experiences and information about this.

:)

MJCronin (Mechanical) · Answer 7 · 2012-04-18 14:33:27

Regarding your question about a frangible roof design:

1)  Be aware that the ability of a tank roof to fail as desired is in doubt for tanks below 10m in diameter. This has been the subject of many numerical FEA studies and physical testing over the past 20 years.

2)  For tanks up to 50 ft in diameter, it is usually best to include a quality "emergency vent" in the design. The client is happy, the regulators are happy and you end up with a product that has a tested emergency device.

Here is some light reading on the subject:

http://www.thunderheadeng.com/wp-content/uploads/downloads/2010/09/Zhi_Lu_Thesis.pdf

More good stuff:

http://www.nistm.org/houstonSept2009/docs/2009_HoustonConf_Pres/relief_venting.pdf

Good luck....tell us more about your final design....!!!

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