5 replies to this topic

[vaporiser]

All,

I have a closed tank which has operating pressure of say 5bar. It's height is 40 ft. What will be the pressure at the bottom of the tank? Will it be 5 bar or 5 bar + static pressure due to 40 ft?
I know if gas were there , pressure would be 5 bar , but here the case is liquid.
The reason why i am asking this question, because if a tank is subjected to a hydrotest pressure of say 10 bar, how the pressure will be maintained inside the tank.

Thanks

[Art Montemayor]

Vaporizer:

I don’t know what you call the height of your tank. It could be the overall, tangent-to-tangent, seam-to-seam, or simply the liquid height (which you don’t state). But since you mention a hydrotest, I presume that is what you propose to do with the tank. If that is true, then I can assume (or guess) that you mean the overall height (the total height of the liquid inside the 100% FULL vessel).

If that is the case, then the total maximum internal pressure imposed on the vessel is the hydrostatic pressure registered at the very top of the vessel PLUS the pressure of the hydrostatic head of water (the overall height of the vessel). I don’t understand what you mean by the phrase “how the pressure will be maintained inside the tank”. Is it meant as a question or a statement?

[fallah]

All,

I have a closed tank which has operating pressure of say 5bar. It's height is 40 ft. What will be the pressure at the bottom of the tank? Will it be 5 bar or 5 bar + static pressure due to 40 ft?
I know if gas were there , pressure would be 5 bar , but here the case is liquid.
Seems the tank is designated to be full of liquid,if so the pressure at the bottom of the tank Will be 5 bar + static pressure due to 40 ft.
The reason why i am asking this question, because if a tank is subjected to a hydrotest pressure of say 10 bar, how the pressure will be maintained inside the tank.
During hydrostatic test of such tank,let say 10 bar,this pressure should be maintained at the top of the vessel.
Thanks

[JaluceroL]

Vaporiser:

Bottom pressure in your tank will be:

Pb = P0 + rho*g*h

where:

P0 is static pressure, in your case 5 bar
rho is the fluid density, kg/m3
g is the gravitational acceleration, 9,81 m/s2
h is the liquid level in your tank, m

rho*g*h gives units of pressure, in this case Pa.

If static pressure will be at 10 bar, then tank should be full filled with water, and then pressure should be increased up to 10 bar, since water is an uncompressible fluid, small amout of water will rapidly increase pressure.

[vaporiser]

[quote name='Art Montemayor' timestamp='1304342961' post='48198']



Vaporizer:

I don't know what you call the height of your tank. It could be the overall, tangent-to-tangent, seam-to-seam, or simply the liquid height (which you don't state). But since you mention a hydrotest, I presume that is what you propose to do with the tank. If that is true, then I can assume (or guess) that you mean the overall height (the total height of the liquid inside the 100% FULL vessel).

If that is the case, then the total maximum internal pressure imposed on the vessel is the hydrostatic pressure registered at the very top of the vessel PLUS the pressure of the hydrostatic head of water (the overall height of the vessel). I don't understand what you mean by the phrase "how the pressure will be maintained inside the tank". Is it meant as a question or a statement?


Art Montemayor,

When I said "how the pressure will be maintained inside the tank", I meant it as a question. My question is how will the pressure be maintained uniformly throughout the tank? Let me try to make it clear. Let's say tank is fully filled & operating pressure is 5 bar. Also, static pressure at bottom of the tank is 10 bar. So, pressure at the bottom is 15 bar. Now if this tank is subjected to a hydrotest pressure of atleast 15bar, I have following questions:
1. Will the hydrotest pressure of 15 bar be at the top or at the bottom?
2. If it is at the top, then pressure at the bottom will be 15 + 10(static) = 25 bar. So, tank is not subjected to a uniform pressure of 15 bar (at top it is 15 bar & at bottom it is 25 bar). I believe this will have an impact on material selection & wall thickness. My question is material selection & wall thickness should be against 15 bar or 25 bar?

I hope I have made my question clear. Looking forward to your quick response.
Thanks

[acer_asd]

This has made your question more clear.

When you say that you have to hydrotest a tank at 15 bar, it generally means that pressure at top will be 15 bar and obviously at bottom pressure will be 25 bar (if 10 bar is static head of the water).

Regarding wall thickness, tanks are designed in such a way that wall thickness increases as you move from top to bottom to take care of the static head of the liquid. Hence wall thickness is NOT UNIFORM.

From your question it seems that you already have the tank which must have been designed with higher wall thickness at the bottom. So you just check from the datasheet that how much pressure it can withstand at bottom and top.

hope this answers your query

have a nice day