External Pressure Calculations interpretation

[Awais371]

thread794-274016
Greetings,

I'm designing a horizontal pressure vessel of 1372 mm Inside diameter and 4062 mm tan/tan length. With 2:1 SE Head the stiffened length is 4290.67 mm (tan/tan length + 1/3(343) 1/3(343)). PV-Elite uses the same for required thickness under external pressure. But PV-Elite also calculate for maximum stiffened length which is 7292.8 mm (more than overall length of vessel).
Can anyone please clarify how this 7292.8 mm Maximum Stiffened Length is calculated?

 

[Maslov]

It looks like it is calculating the maximum permissible length for a vessel with a 9mm wall thickness to achieve a MAEP of 1.03 bar (so roughly full vacuum).

So it is not really relevant to your actual vessel, the program is simply telling you how long you could make the vessel.

As for how you calculate it, simply do UG-28 in reverse order (start with external pressure -> calculate B -> determine A -> determine L/Do -> calculate L).