External Pressure and Stayed Jacket

[wailunwu]

A vessel with internal design pressure of 21.737 psig is to be designed with full vacuum. A stayed jacket is also added. What is the pressure between the stayed jacket and vessel shell wall that I should be using when doing thickness due to 'external' pressure calculation for the vessel wall?

Will it be:

a) 15 psi
b) 15+21.737 psig
c) Other 'external' pressure?

I have only entered 21.737 psig as internal design pressure and 15 psig as external design pressure into PV Elite. But PV elite has the following calculation generated:

Inner Shell (Core) External Design Pressure [extDP]:
= Jacket Internal Pressure + Shell Vacuum Pressure
= 21.737 + 15.000
= 36.737 psig

I would like to know why that's the case (choice b). What is the reason behind using internal design pressure as additional 'external' pressure for the pressure vessel?

Note: I used quotations on the word 'external' because it actually is the pressure between the jacket and the vessel walls.

Thanks

 

[marty007]

Think of the worst-case scenario...

The inner pressure vessel is under full vacuum: 0 psia
The jacket is at design pressure: (21.737+15) psia = 36.737 psia.

The effective external pressure acting on the inner shell is 36.737 psi.

Cheers,

 

[wailunwu]

@marty007

Although I have only indicated Vessel Internal Pressure as 21.737 psi in PV Elite, the PV Elite report says:

Input Values:

Jacket Design Internal Pressure Pj 21.74 psig
Jacket Design External Pressure Pje 15.00 psig

Why does Vessel Internal Pressure equal to Jacket design internal pressure? To me, the jacket design internal pressure is refering to the space between the vessel shell and the jacket, which is independent of the space inside the vessel. Per you reply above, "The jacket is at design pressure: (21.737+15) psia = 36.737 psia." What pressure is this referring to? Internal or external of the jacket?

 

[marty007]

Just to clarify, what are the design conditions in the vessel and jacket?

From what I gather in your post, so far I see:

Vessel:
Internal Pressure: ? (not yet discussed)
External Pressure: 15 psig (full vacuum)

Jacket:
Internal Pressure: 21.74 psig
External Pressure: 15 psig (full vacuum)

Are these values correct?