Stresses:
Let a thin spherical shell of nominal diameter d & shell thickness t which is having some fluid at an internal pressure p .
Figure
Spherical shell is symmetrical in all of directions and therefore, it shall have a tendency to burst equally in all of directions hence, one can decide the hoop or circumferential stresses in the material shall be the similar in all directions. We will consider a diametrical plane XX which cuts the shell two halves of hemispherical segments; we will consider the upper hemispherical portions and see the nature and magnitude of the internal stresses working on the reaction. The stresses shall be as illustrated in Figure .
Figure
For the upper half of the shell assumed, the equilibrium is attained by the hoop stresses σh set up normal to the section of the shell wall that is cut and exposed. The internal pressure of fluid working on the internal surface of the shell induces a bursting force. It is resisted by the hoop stresses σh working vertically down and tensile in nature.