AMETANK DESIGN PRESSURE, IN GUAGE OR ABSOLUTE PRESSURE?

[Omuye]

Hello Team,
Good day to you all.

please I will like to find out, if the pressure unit in AMETank Software is in gauge or absolute?

This is because I am design a crude oil storage tank and the design pressure is 1psi. But when I input my design pressure of 1psi (6.8kpa) the result I get from AMETank tells me that the design pressure is more than the maximum allowable working pressure. And this is a recurring warnings in my designs of tanks.



Please help to clarify.

Thank you.

Regards,
Efe

 

[JStephen]

I'm not familiar with that software, but normally tank pressures would be in gauge pressure.
If the tank is of any considerable size, 1 psi is a "high" pressure. In pressure vessel terms, it may be negligible, but applied to a very large roof area, it can generate large uplift forces at the base of the shell, and large compression forces in the top angle area.
If the software gives the option to calculate the maximum design pressure, that might be informative.
Note that if Annex F is not specified, it will be limited to the weight of the roof plates, which is around 8 psf (pound per square foot, not per square inch).
Otherwise, if the tank is "large", figure the tank will be anchored, the compression ring will be built up much larger, and for a cone roof, the roof slope will be increased.
For a large tank, 1 psi design pressure can be a substantial increase in the cost of the tank and the foundation.

 

[LittleInch]

Yes, that was my question also.

Where does 1 psi come from?

API 650 tanks and similar large storage tanks are "atmospheric" pressure.

That means something like 1 kPa or inches of water column.

1 psi sounds like something someone has decided who doesn't understand large storage tanks. Is that you or someone else?

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

 

[Omuye]

Hello,

Thanks for the prompt response.

@JStephen, actually the tank dimensions is 40mD x 17.5mH. Now in putting design pressure of 1psig is generating a large uplift force at the base and large compression force in the top angle area.

Below is the warning I am getting from the AMETank software using using design pressure of 1psig (6.8kpa)
Warnings!!
Initial Data
1.- Design internal pressure is greater than maximum allowable working pressure (MAWP).

Top Member Data
1.- Design internal pressure is greater than maximum allowable pressure per API-650 F.4.
2.- As per API-650 F.5.1, top member region cross sectional area, 25,168.68 mm^2, is less
than the required value of 42,727.99 mm^2.

So I feel the design pressure for the tank is meant to be ATM i.e. 0psig. And I am assuming the design pressure specified on the process p&id as 1psig was meant to be 1psia and NOT 1psig because the tank is atmospheric.


@LittleInch, I believe the design pressure may have been wrongly specified 1psig.

 

[JStephen]

There may just be an error in the data sheet. The 1 psia wouldn't make sense, either, that's a huge vacuum in the tank.
It's not uncommon to see an unreasonably high pressure specified because the person specifying didn't realize the effects of it, and some back and forth conversation may clear the issue up.

 

[Omuye]

These are the input parameters for the API Tank I am designing:
Tank diameter = 40m
Tank height = 17.5m
design pressure = 1psig
design temperature = 40.6degC
product stored = crude oil
product specific gravity = 0.9
corrosion allowance = 3mm
joint efficiency E = 1.0
Tank material = A516-70

So, my thought is that, may be the pressure may have been wrongly specified as 1pisg instead of ATM.

 

[jari001]

Does the software Help menu not have a page with the default unit spread based on system chosen? Also, maybe there is a test simulation you can run to deduce the units based on comparing simulation output to hand calculations?

 

[Geoff13]

t's not uncommon to see an unreasonably high pressure specified because the person specifying didn't realize the effects of it, and some back and forth conversation may clear the issue up.

In my experience this is exactly the problem. You need to talk to your customer so you can explain why they need to revise their datasheet. I would suggest running a number of smaller pressures so you are able to show them how the costs vary and they can select what best suits their needs. They should consider both tank and foundation costs.

FYI : 1 psia would be even more impossible to design for than 1 psig on an API tank.

 

[LittleInch]

So, my thought is that, maybe the pressure may have been wrongly specified as 1pisg instead of ATM.

That sounds correct to me. I suspect that this was filled in by a junior engineer who didn't think putting zero design pressure was the right answer so put in the lowest pressure he or she could think of without knowing the consequences.

So back to your client or internal team member.

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

 

[IFRs]

There is no reason to desing a crude oil storage tank for any internal or external pressure. Especially one of that size. They are typically extrenal floating roof tanks or fixed roof tanks with internal floating roofs. Now is the time to question the design pressure, not to figure out software or other details. Garbage in yields garbage out and you have a clear case of garbage in.

 

[Omuye]

Hello Team,

Thanks for your responses. Obviously the desing pressure was wrongly specified and the pressure has been updated to ATM pressure.

Many thanks.