API 650 Roof Weight 3

[tzh0044]

When calculating the weight of the roof for an API 650 tank, are nozzles and flanges on the roof also added? The scope specifically say "roof plates" which makes me assume not. If not, what about the weight for Annex F?

 

[JStephen]

Nozzles and flanges could be included (similar to roof structure attached to the roof), but are usually neglected for simplicity. Quite often, details and weights are not known when the roof is designed. Usually, roof nozzles are not symmetrical around a tank, and that lack of symmetry is not addressed in the standard, either.

 

[tzh0044]

When working through Annex F.1-F.7, I calculated F.1 and F.4 by hand and got pretty similar number as my analysis software. But for the equations (1), (2), and (3) the software is taking the minimum of those, then the max of that of 0. So my design pressure is 0 psi, why is it doing that? My physical copy of API 650 doesnt have that step.

 

[tzh0044]

JStephen, from your experience would you use the nozzle weights if you had an existing tank that you were trying to determine the MAWP for? Also I've been reading through API 650 today and when Ive needed a better understanding, your name has popped up on other threads. Thanks for all the help!

 

[Jay_]

There is something off with you calculation.
Can you share the basic design data.
Design pressure, diameter, height, type of roof, slope, roof and shell thicknesses, wind speed?

Detailing is a hobby,

 

[tzh0044]

Design pressure is unknown (existing tank and Im trying to determine that) 10' ID, 20' height, self supporting cone type (detail d), 2:12 slope, 5/16 thk, 115 mph

 

[r13]

I am looking at API 650 [2007], in which, it says the maximum design pressure should be calculated by F4.1, but not to exceed the value calculated by F4.2 and F4.3. Seems the equations are quite different than yours.

 

[tzh0044]

Those are subject to the limitations of F.4.2.

The equations I have shown are from F.4.2

 

[Jay_]

It does seem that your wind uplift pressure on the roof is high on such a small tank.
It’s late here i wish i could help more.
Revise your software inputs

Detailing is a hobby,

 

[tzh0044]

I'm unable to calculate the value for RMW the same by hand.

I'm doing - vertical pressure * pi * radius * radius * radius + diameter * height * horizontal pressure * height/2

Am I doing that moment calculation correct?

 

[Jay_]

Check table 5.20a

Detailing is a hobby,

 

[r13]

In your RMW calculation (I assume it is overturning moment by wind that causing uplift), the second term is correct, what is the first term "pi * radius * radius * radius" [ = (circumference/2)*radius²]?

 

[tzh0044]

pi * radius * radius for area then radius again for the moment arm.
vertical pressure * area * moment arm

so the 3rd "radius" is the moment arm. The way I typed it wasn't clear.

 

[r13]

I see. Then where is the pressure term for it?

 

[tzh0044]

The vertical pressure is the internal pressure, right?

 

[r13]

It should be uplift by wind suction on the project roof area, an external force that produces overturning effect. I don't think internal pressure contributes to the moment. Anyway, the first term shall looks like "Roof Area*Pressure*Lever arm".

 

[JStephen]

I missed the followup posts to this.
But one thing to note, that API has revised the wind uplift/pressure/overturning criteria seemingly with each addendum/edition.
So there is no assurance at all that a tank meeting the requirements of one edition will comply with the uplift requirements of a different edition.
Refer to API-653 to see whether the as-built standard or the current standard should be used for re-design/re-rate, etc.

 

[HTURKAK]

Dear Tristin (Mechanical),
I missed this thread . Today morning looked to thread and responds. If your query still valid, will you pls share additional data ( steel material, anchors, content and (if any ) assessment data..).

I think the software that you use, checks the tank as per API 579 (Fitness-For-Service ) with assumption of PV. IMO , the tank should be checked as per API 653 Section 4.

 

[tzh0044]

I will look into API 653 as directed, thanks for all the help!