API 650 Pressure Limit 8

[Rigrid]

Hi everyone, related to AST API 650, I would like to discuss as follow: the pressure limit 2.5 psi means 14.5 psi + 2.5 psi, thus the pressure limit become 17 psi, is my understanding correct?

please share your thought, appreciate your help

 

[mk3223]

It’s the Code for the tank design up to 2.5 psig. Not up to 17 psig.

 

[Rigrid]

@mk3223 thank you for the answer, so API 650 standard was designed for Tank below Atmospheric Pressure?

since the atmospheric pressure is 14.5 psi at ambient temperature, CMIIW

 

[mk3223]

The Code is for the tank at the pressure up to 2.5 psiG (gauge pressure).
The atmospheric pressure is 1 ATM or 14.5 psiA (absolute pressure) or 0 psiG.

 

[georgeverghese]

Max vacuum pressure permitted in API650 is 2.5in water column, which converts to 100.69kpa abs or (100.69-101.33) = (-)0.64kpag.
Pls note the setting of a vacuum RV on an API650 tank is typically no more than 80% of the max permissible vacuum pressure it is mechanically designed for (i.e. 20% accumulation is implied)

 

[LittleInch]

Rigrid,

You are wrong.

When codes use psi, they mean psig, I.e. pressure above local atmospheric pressure.

The vast majority of API 650 tanks are designed to be "atmospheric" pressure.

F2.1 states that pressures less than 1kPa or 4 inches of water do not need to be included and therefore are classified as "atmospheric"

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

 

[HTURKAK]

The relevant clause of API 650,

F.1 Scope
F.1.1 The maximum internal pressure for closed-top API Standard 650 tanks may be increased to the maximum
internal pressure permitted (18 kPa [2.5 lbf/in.2]) gauge...

By definition , API 650 uses gauge pressure .
....

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[Rigrid]

hi everyone, thank you for the responses, I apologize that I cannot reply to each response, here what i can conclude from the discussion:

- if we use absolute pressure then the pressure limit is 17 psi (IMHO, for absolute pressure it's not a must to add letter A)
- if we use gauge pressure then the pressure limit is 2.5 psiG (I'm adding letter G to the psi unit to note that this is the gauge pressure)

p.s.: atmospheric pressure at sea level is approximately 14.5 psi, the 17 psi is come from 14.5 psi + 2.5 psi, if we use gauge pressure then atmospheric pressure will be 0 psiG, CMIIW

Again, thank you very much for the help, and I'm sorry if I'm not polite enough when replying, I'm trying my best to be polite enough

 

[LittleInch]

You will get into a lot of trouble if you don't use "A" to indicate Absolute pressure.

The vast majority of codes, standard, designs etc assume that "psi" means gauge pressure. not adding "a" afterwards is IMHO, quite dangerous and poor practice. Also note that atmospheric pressure can easily vary by 6 or 7 psi as you get up to high altitude but still on the ground. Hence your 17psia or 2.5 psiG could then end up being 10 psig....

It's only process engineers that like to use psia....

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

 

[Rigrid]

MJCronin buddy, why do you have to offense people that way? do you feel great by doing this?

anyway I'm an engineering graduate and work as a Mechanical Engineer, and please kindly do not use presumption when judging people

LittleInch, thank you for the correction

 

[MJCronin]

Rigrid...

You stated:

- if we use absolute pressure then the pressure limit is 17 psi (IMHO, for absolute pressure it's not a must to add letter A) - if we use gauge pressure then the pressure limit is 2.5 psiG (I'm adding letter G to the psi unit to note that this is the gauge pressure)

... and this is a DANGEROUS STATEMENT in my opinion .... No one, however seems to agree

...and like most of the third-world, instead of talking about substantive technical issues, you "clutch your pearls, faint and cry that your delicate feelings are wounded !!!... OMG ... If you are truly a delicate flower, perhaps you don't need to be here !!

... and then you personally attack me ....

I am not being offensive, I am using mild sarcasm and some hyperbole (look it up) to make a point ...
I have not used any vulgarites or swear words ... If you dislike what I say ... Ignore me !!!

=====================================================================================
a quick poll here ...

1) ---- How many agree with the "RIGRID statement above where the suffix "A" should be optionall in all psi designations ?

2) ---- How many agree with the "RIGRID statement above where HIS NEW suffix "G" should be used in designations ?

I do not think your new designations are good idea... (too strong ?)

LittleInch always gives good, solid advice ... BRAVO, sir ...

MJCronin
Sr. Process Engineer

 

[JStephen]

Generally, it's fairly obvious which is intended.
For force-based issues (design of tanks, vessels, tires, hydraulic issues), usually psig (or psf or inches of water column, which are also gauge pressures).
For thermodynamics, chemical reactions, fluid/vapor flow, usually psia.
It's always appropriate to clarify which is being used, not always necessary though.
I see and use these as all lower case, psia/ psig, not psiA or psiG.
Note that in tanks, pressure and vacuum are always gauge values for the tank design. But then when specifying when an internal floating roof is allowed/ required, the limitation on vapor pressure is given in psia. I think some of the vent flow rate calculations require working with absolute pressures as well.

Personally, I don't feel the continued attacks on people due to assumption of their youth, nationality, or presumed MBA status really do anything to promote engineering knowledge or professionalism here.

 

[KevinNZ]

Tank and vessel design is concerned with the difference between the inside and outside pressures. This what you would see a on gauge pressure gauge connected to the inside pressure. We often design vessels for installation above 2000m and you can not say the pressure X bar.a - 1 bar as the external pressure is lower than 1 bar.a

Pressure gauge is also what your over pressure protection device will act on.

Do not specify vessel/tank design to pressure absolute. All/most the equations in the codes refer to the pressure difference between inside and outside.