Is it mandatory to check for all the pressure vessel for external pressure when they are being designed for internal pressure?

Hello Naveen

The simple answer is no. ASME, and indeed any other code does not require the vessel to be analysed for external pressure when there is no external pressure.

DEAR RAY,,

IN MY CASE VESSEL INTERNAL DESIGN PR IS ATMOSPHERIC AND ALSO VESSEL EXTERNAL PR. IS ATMOSPHRIC.

WHEN I CALCULATE USING PVLITE 6 MM THK IS OK FOR INTERNAL PR. BUT FAILING IN THE EXTERNAL PRESSURE. IN THIS CASE SHOULD I GO FOR NEXT HIGHER THICKNESS OR IGNORE THE WARNING.

Hello Naveen

If you enter a zero external pressure for all the elements, the programme checks the maximum external pressure the vessel can take, but it should NOT give any warning. You have possibly entered an external pressure for one or more elements. That is the only thing I can think of.

Dear Ray,

Pl. clarify me that if vessel is to be checked for Full vaccuam condition what should I enter in the field of External pressure

1.033 Kgf/cm2 (1 Atm)

or

Zero

Regards

Mr. Naveen,

The vessel should be designed for maximum differential pressure,whether internal or external.Full vacuum means internal pressure is zero and external pressure of 1.033 Kgf/cm2 is acting on the vessel.Thus, maximum external differential pressure acting on the vessel is 1.033 Kgf/cm2. So, you should enter 1.033 Kgf/cm2 in the input field.
If in case your vessel is failing under external pressure calculation, you either increase thickness or provide stiffning ring.

Regards
Saurabh Gajwani

If a vessel a vessel is subjected to full vacuum, and the vessel is to be code stamped, the code says the pressure to be used is 15 psi. This equates to:

1.03421 bar
1.0546 kgf/cm^2
103.421 kPa
etc...