Pressure Vessel External Pressure

Because for external pressure you have to to consider the external forces while weight of liquid and weight of vessel are internal forces, Dear it is very clear and simple...

Notation

W= Weight of shell above the considered section

Me = external applied moment from wind OR seismic, including piping reactions at the considered section

Z=I/v= Modulus of resistance of considered section , in [mm3] or [in3]

A= Section of considered section

P= External pressure

Next to the ASME consideration given in UG , for wich the factors A and B , L/Do and D/t have to be considered and from which you have to calculate the maximum allowable pressur = B which shall be B => external pressure

You have to check the following=

Sigma_axial =External presure +(W/A) + (Me/Z) , (all compressing the shell)

This sigma_axial has to be lower than B , this means no buckling shall occur

And if not satisfied than you have to increase B , by adding stiffeners or increase thickness etc

The above is indicated in ASME VIII div 1 , appendix L , where you have worked examples

Other textbooks , such as the ones from Bednar (Pressure vessels handbook ) or Megeysey discuss this

Also foreign codes ( PD5500 or EN ) do also talk about it

Salam

Fathi

Thanx for your notation which i already realize, From your previous notations there is no consideration of weight of liquid inside the vessel to calculate the external pressure, that is specifically what you were asking about, So is up to you, take it or leave it. Thanx,