INTERNAL PRESSURE FOR DIESEL FUEL OIL-VERTICAL STORAGE TANK 1

[Jay_]

Hello everyone,
if you are designing a storage tank according to API 650, that eventually will be containing diesel fuel oil #2.
does the tank needs to be designed with internal pressure of 2.5 PSIG (EQUAL TO THE PRESSURE RATE OF THE EMERGENCY RELIEF VALVE)?


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[GT-EGR]

Depends on what you mean by designed. It should be expected to normally operate at atmospheric pressure (assuming you have a normal vent to atmosphere). But the tank does need to be able to hold up to what your emergency relief valve is set to - so if pressure does buildup from some abnormal condition, the tank stays together and the emergency venting is directly towards the designed weak point which is the emergency relief valve.

 

[Jay_]

Should we consider using an emergency venting in case of having an open vent at the roof of the tank (diesel fuel oil case).??
IF YES...
then the high internal pressure should be taken into consideration in the design process?? or not since it has open vent then the internal pressure should be atmospherical?
IF NO...
The tank will be designed simply to operate atmospherically.



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[Geoff13]

I'm used to larger tanks (50' dia and greater). A pressure of 2.5 psi would cause most tanks to explode.

While API 650 does permit the pressure to be higher than design pressure (see clause 5.8.5.3) during emergency venting conditions, I would expect only a very few high pressure Annex F tanks to permit 2.5 psi during emergency venting.

To save me more typing please also see my other reply today in this thread : thread1452-456684

 

[Jay_]

Thank you again sir!
But basically as a rule of thumb,
On which design pressure (internal) shall you design the above mentioned tank.
Tank contents is fuel oil #2.
Dia 25 meters x 18 meters height.
Any assumptions would be appreciated!!

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[LittleInch]

Jay.

Read API 650. It is designed for "atmospheric" tanks. That means what it says. At best the pressure is measured in single digit inches of water.

Your 2.5 psig is basically unheard of and there is no need to have any pressure when storing diesel.

The pressure on the tank is simply the weight of its contents (you need to base it in water which is used to test the tank).

This is a big tank. Buy it from a vendor who has made one before.

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[Jay_]

The only thing I’m confused about is the amount of pressure the vapor of diesel have in emergency situations.
Should the tank be designed to withstand this pressure or only in normal operation??

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[LittleInch]

What "emergency" are you thinking of here?

Tanks and vents need to be designed to cover all reasonable situations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

Normally, for a large tank like that the tank details would be established, the maximum allowable pressure based on those details would be determined by the designer, and the vents would then be sized based on those pressures.
There is allowance in API 650 to use a higher set point for emergency venting than for normal venting.
If the roof qualifies as a frangible roof per API-650, then emergency venting is not required.
For a tank with a "free vent", the most economical emergency vent may be to simply increase the size of the free vent.
A tank of that size could be designed for 2.5 psi, but it would be a considerable increase in cost and complexity, and foundation cost, and would never be done for a diesel tank.

 

[Geoff13]

API 650 uses the term "emergency" for the case where there's a fire outside the tank causing the product to boil, and thus a much higher venting capacity is required.

 

[Jay_]

Thank you all for the clarifications! They were very helpful.
One question tho, in your experience, which product require a high design pressure?
Design pressure are normally determined by a process engineer but i’m curious.

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