The document provides formulas for calculating stresses in thin-walled pressure vessels. The circumferential (hoop) stress is calculated as the internal pressure multiplied by the inside diameter divided by twice the wall thickness. The longitudinal stress, which also applies to spheres, is calculated as the internal pressure multiplied by the inside diameter divided by four times the wall thickness. These formulas are only valid if the wall thickness to radius ratio is less than 0.10.

1. XI.) Stresses in Thin-Walled Pressure Vessels A.) The following formulas are valid only if the wall thickness-to-radius ratio is small enough, i.e. : t_ < 0.10 r i or, based on diameter: t_ < 0.05 so, t < 0.05 D i D i

2. Circumferential Stress (hoop stress):  t,c = pD i 2t Longitudinal Stress (also applies to spheres):  t,L = pD i 4t D i = Inside Diameter (in.) p = Internal Pressure (psi) t = wall thickness (in)