Elastic stability:
Critical bucking stress: 
The maximum compressive stress will occur when the vessel is not under pressure
= 8.83 + 69.06 = 77.83 N/mm2
The value 77.83 is well below the critical buckling stress. Therefore design is satisfactory.
Example 3: Determine the shell thickness for a tall vessel of following specification. As a generation guide it is to be noted that for each 5.6 m height, shell thickness can be increased by 1.2mm. This general guide is required to determine the number of shell courses.
Max wind speed expected (for height up to 20 m) = 150 km/h
Shell outside diameter = 2.5 m
Shell length tangent to tangent = 18.0 m
Skirt height = 3.8 m
Operating temperature = 310°C
Operating pressure = 0.6 MN/m
Design temperature = 330°C
Design pressure = 0.9 MN/mm2
Corrosion allowance = 2.5 mm.
Tray spacing = 0.7 m
Top designing space = 1.0 m
Bottom separating space = 2.5 m
Weir height = 80 mm
Down comer clearance = 30 mm
Weight of each head = 7.5 KN
Tray loading (excluding liquid) = 1.0 KN/m2 of tray area
Tray support rings = 50mm x 50mm x 10mm angles
Insulation = 70 mm asbestos
Weld joint efficiency factor = 0.85