Size and definition of storage tank; API 650

[eng741]

Hi all,

I have a P&ID that give the following info.:
Size: 50'-8"O.D. x 42'-0"HG.
CAP: 15,000 BARRELS
PRES: DESIGN: 3P/2V OPER: X PSIG
TEMP: NORMAL 60 F
MATERIAL: CARBON STEEL

The height of the tank from a drawing is 42'-0" from the bottom shell to the very top shell.

My three questions:
1) What is the HG behind 42'-0"? I typed 42'HG in google and it assumed it as ft Hg (pressure). When I converted 42 ft Hg to pressure it was 247.54 psi.. but the tank is under 2.5 psi since it follows API 650.
From API 650 in sec. 5.5.2 it has two definitions:
H: The maximum design liquid level (see 5.6.3.2), in feet
G: The design specific gravity of the liquid to be stored
API 650 5.6.3.2 has a further def. for H:
H: the design liquid level, in ft.
is the height from the bottom of the course under consideration to the top of the shell including the top angle, if any; to the bottom of any overflow that limits the tank filling height; or to any other level specified by the Purchaser, restricted by an internal floating roof, or controlled to allow for seismic wave action.

2)What does the top angle mean in this case?

3)Lastly, on PRES: DESIGN: 3P/2V.. what does the 3P/2V mean. I'm assuming 3 pressure/2 vacuum but I wanted to make sure.

Thank you in advance,

eng741

 

[bimr]

1. HG = High or Height. Normally, the height would refer to the straight side, including the top angle. The straight terminates at the shell roof joint.

2. The angle is a stiffening angle welded to the top of the side sheet all along the tank circumference.

3. P and V are definitely pressure and vacuum. However, the API 650 is for atmospheric tanks. For API 650 tanks, the maximum Design Internal Pressure (P: Shall not exceed 18 kPa (2.5 lbf/in.2). Probably is 3(in. of water)P/2(in. of water)V.

 

[IFRs]

Your specification calls for 3P/2V design and "OPER: X PSI". Since the operating pressure measured in psi I suspect that the units for the design pressure/vacuum are also in PSI. Before you go any further, clarify the units for pressure/vacuum, as bimr stated, API 650 may not be your code.

 

[eng741]

Thank you for the immediate responses.

I will ask the company about the operating pressure.
I assumed the design pressure would be higher (3P/2V) and the operating pressure would meet API 650 since the drawings I have say per API 650.

Thank you again for the help,

eng741

 

[JStephen]

A tank that size built to 3 psi will have some substantial modifications and cost impacts due to the pressure.
I believe API-650 includes only up to 1 psi on the vacuum side, but would have to confirm.
Also review carefully the API-650 provisions relating to design pressure, operating pressure, and venting. The operating pressure will not be the design pressure, for example.

 

[eng741]

Thank you for the advice, I will look more into it

eng741

 

[Duwe6]

Hopefully "3P/2V" indicates inches or cm of Water Column. Or possibly [but not very likely] 'OSI' ounces per inch^2.

PSI is not an appropriate measure for API 650 Atmospheric Storage Tanks.

 

[tankSnvessels]

Dear eng471,
I agree with bimr's three answers. "bimr" replied you to the point as I would.
1) HG.= High or Height (HT/HG)
2) Shell highest level stiffening angle
3) I support your understanding: 3 PSIg internal pressure and 2 PSIg Vacuum pressure

 

[eng741]

Thank you all for the help, it is much appreciated