HOW TO CHECK A VESSEL WITH INTERNAL PRESSURE 700 PSIG FOR FULL VACCUM CAPABILTY.

My understanding is that enter 14.7 psig in external pressure box keeping the internal pressur
700 psig


is it corect or not

Dear Yatish,

If the vessel is to receive a Code stamp, the design external pressure should be 15 psig external pressure.

The program analyzes internal and external pressure separately as either condition may occur. So, it is correct to enter both an external and internal design pressure.

it means for full vaccum capability can be checked while doing calculations for Internal pressure 700 psig by putting 15 psig in external pressure box

current practice in india is people do seperate calculations
1) first calculation -put 700 psig in Internal pressure and atmospheric pressure in external presure
2)IInd calculation-put 0 psig in Internal pressure and 15 psig in external presure

mandeep sir please clarify it..

i need to design the vessel for internal pressure of 70 kg/cm2 as well as full vaccum (Interal ) conditions. so there are two cases now

case 1) for 70 kg/cm2 pressure i am considering 70 kg/cm2 as a internal pressure and 1 kg/cm2 as external pressure.
correct me if i am wrong.

case 2) For internal vaccum condition what shoud i consider because , vaccum means there is no pressure inside the vessel but we cannot put zero as a internal pressure since ASME does not support vessel for internal pressure less the atmospheric pressure.

so what shall we do ??? can we do like, put 1 kg/cm2 as a internal pressure and [ atmospheric pressure + 1 kg/cm2 ( i.e. 2 kg/cm2 )] as a external pressure ???


please clarify , awaiting your valuable reply.


Thanks

You don't enter the actual pressures in the internal and external pressure boxes in PVElite. You enter the gauge pressure for which the vessel has to be designed.
So if your vessel has to be designed for, for example, 10 bar internal pressure and full vacuum, you enter 10 bar in the internal pressure field and 1 bar in the external pressure field.

Two design calculations will now be done in one file:
1. 10 bar(g) internal design pressure, for example a situation with 11 bar(a) in the vessel and 1 bar(a) outside the vessel.
2. 1 bar(g) external design pressure, for example a situation with 0 bar(a) in the vessel and 1 bar(a) outside the vessel.

thanks Corne,


as you said we are putting the gauge values of pressure in PVElite however as u explained above 10 bar internal pressure & Full Vaccum case if u entered 10 bar as a internal and 1 Bar as a external, then what will u enter for atmospheric external pressure then ???

You don't have to enter the atmospheric pressure.
If you enter 10 bar internal and 1 bar external pressure, the vessel will be designed for those two situations, so:
10 bar internal pressure: this means 10 bar gauge internal pressure. This can reflect a situation where the pressure in the vessel is 11 bar absolute and the pressure outside the vessel is 1 bar absolute (atmospheric). But this can also be a situation where the pressure inside the vessel is 20 bar absolute and the pressure outside the vessel is 10 bar absolute (for example a jacketed vessel).

PVElite does not combine the internal and external pressures. These are gauge pressures and need to be evaluated seperately.

Pramod,

I think you have to go through the definition of "FULL Vacuum" to clear your mind. Full Vacuum is the condition of vessel in which the pressure inside the vessel is absolute zero i.e. there is no pressure inside the vessel. But outside pressure is atmospheric (generally), so we have to keep 15psi i.e. 103.4kPa during designing Full Vacuum condition.

Susan
Kuwait