Hi guys.

When designing an atmospheric tank, do we need to put the external pressure as 0? Previously i was made to understand that an atmospheric pressure input value will be 1 atm at external pressure and 1 atm + liquid level at internal pressure. However in PV Elite, the software will treat it with two scenario, which each pressure value alone, given the shell thickness increased drastically (example 2430 dia, tr = 3.00, trext = 11.5mm). Thus what is the correct way of inputting value for pressure when designing an atmospheric tank?

Hi Fitri,

If the tank you are designing will never be subjected to a vacuum, then the external design pressure can be set as zero. If there is any possibility that this is not the case, then you should design for an appropriate vacuum, which may be a partial vacuum.

So the real question is in determining all the design scenarios that relate to the pressure and making sure they are all accounted for. As you may know, large thin cylinders are weak under vacuum conditions.

Dear Scott,

Thank you for your kind reply. Would you mind pointing me a good reference to study against these scenario? I`m still not convinced of what value should we put at external pressure since i need to consider partial vacuum might appear during process.

Hello Fitri

The information given to you my Scott is all you really need. If you enter a zero in the external pressure field, PV Elite will not do the full analysis for external pressure, although it does that calculation for INFORMATION ONLY which you can ignore.

The best study reference is the ASME Section VIII code at sections UG-28 and UG-33. There you will find the full details of the procedure set out step by step.

Dear Ray,

Thank you for your guidance. I`ll be sure to look it up