Liquid Level Related Tank Design per API 650 Code

Dear rajkumarabirami

Greeting to you

In most cases of tanks which have inside diameter less than 60 m - and designed by 1- foot method according to API 650 - limited by the plate thickness of the bottom course, which should not exceed 1.5" (38 mm).

The term of (H) in the equation of thickness refer to the design liquid level, for more safety in calculations you can take (H) equal to total tank height for substituting in the equation of thickness only.

The process engineer has all responsibility to evaluate this liquid level, but in a general the total height of any storage tank used in the refining field equal to the design level plus 10% of this level specially in the case of liquid which have high volatility rate.

This height in the case of using fixed roof (self fixed roof or supported roof), but in the case of using floating roof the tank height equal to the designed liquid level.

Quick calculations of minimum required thicknesses of courses for Outer Tank diameter x height = 39 m outer tank inside Dia * 11.5 m height. Using private excel sheet.

Then you can select the nominal thicknesses for each course

Quick calculation of minimum required thicknesses for Inner Tank diameter x height = 33 m outer tank inside Dia * 10.84 m height. Using private excel sheet.

Then you can select the nominal thicknesses for each course

yes i agree sir,

but some body wants to insist the design liquid level consideration above the tank height level is it possible. that coversation also i noted here, please find below that,

but somebody suggest me, total tank consideration only enough to find out the shell thickness calculation.

which one is correct?

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During my quick check on shell thickness calculations, I found that new tank T-48350 requires shell thickness higher than the existing tanks. Please note shell design criteria was changed during FEED and hence higher thicknesses are required. Attached please see Shell thickness calculations for both Existing and New tanks.

Existing Tank Shell design criteria : Produced water up to curb angle of outer shell + blanket pressure i.e. 12.5 m.

New Tank Shell design criteria : Saline water up to flange face of blow-off hatch nozzle+ blanket pressure, i.e. 14.0 m.

See tabulation below for thicknesses-

I am of the opinion that this change should be informed to PDO.

PLEASE note the next:

- The maximum liquid level can not - any way - exceed the tank height.

- You can put the term of (H) in the thickness equation: the tank height instead of liquid level for more safety.

- Width of course cans not exceed 2400mm according to API 650

But our client says some notes relevent to design liquid level consideration asper below i noted:

blow off hatch location and elevation shall be finalized such that in case of any instrument level control failure, the liquid level rise beyound the shell-roof(cone) junction upto the blow-off hatch nozzle flange elevation shall not cause damage /failure of the tank shell due to the additional liquid head pressure beyound the cone.

so this liquid level consideration is relevant to blow off hatch instrument.

please consider this also and give a decision relevant to liquid level consideration for shell thickness calculation. for your point of view.

in this case which liquid level instrument can be failed you can use anather type of liquid level instrument like Radar Level Gauge. And if you had to make the liquid level higher than tank height as your client want, make your calculation on (H) term for liquid level not for tank height (for safety in this case) , the thickness in this case will be increased within 2 or 3 mm.
BUT i never saw in my working life before that the liquid level higher than tank height and i can not imagine it.

(Myself also never done this type of design consideration)

But from purchaser point of view, if it is frangible joint it's not possible (liquid level consideration above the tank height) but this one consist a non frangible joint.

and also this is only a precaution action to prevent the shell failure due to over height of liquid head pressure during the operation time, because this tanks are used to separate the oil in water (not water in oil) , which is received cross fluid from oil well. (Purchaser requirement from their practical experience).

and one more thing sir, somebody given a link of this liquid head pressure to stiffening ring. how it is possible, stiffeners can able to withstand this liquid pressure or not?

i can't understood. please find the below conversation between me to bidder,

My question to bidders:

Please note that this design point is different one from normal API 650 design condition (design liquid level consideration for thickness calculation), this one is the client special requirement. It will give the higher plate thickness, ensure and revise the drawings and documents.

Bidder Answer:

The above point has been taken into account. In addition to the shown shell thickness, external stiffeners 4 nos. [Excluding top curb angle] have been considered on the shell to take care of the differential height of liquid levels. Hence thickness of plate shown is adequate.

Please advise me if anything in your mind

.