This sheet uses the calculation in unstiffened cylinders per 8.5.2.2, where L is the unsupported length defined in Figures 8.5-1 and 8.5-2 below. The same calculation may be used also for interstiffener collapse verification (8.5.3.4) as it is safe also in those cases. For stiffened cylinders the unsupported length is defined in Figures 8.5-6 and 8.5-7 below, with the help of Figures 8.5-8 and 8.5-9 and of the formulae herebelow.

L=L's-w''1+0.4h'
or
L=L''s-w'2-w''2
In the case of flanges acting as stiffeners, Figure 8.5-9 defines w from the location of point A.

The circularity tolerance is measured on radius from the true center and shall appear on vessel drawings. It should be verified per Annex D.