1. The cause of curvature of cylinder wall is neglect.
2. The tensile stress are equally spread over the section of walls.
3. The cause of restraining action of heads at end of the pressure vessel is neglect.
While a thin cylindrical shell is subjected to an inside pressure, it is expected to fail in following two ways:
1. It can fail beside longitudinal section (that is circumferentially) split cylinder into two troughs, as shown.
2. It can fail crosswise transverse section (that is longitudinally) splitting cylinder into two cylindrical shells, as shown.
Therefore wall of a cylindrical shell subjected to an inside pressure has to resist tensile stresses of following two types:
(a) Circumferential or hoop stress
(b) Longitudinal stress
(a) Circumferential or Hoop Stress
A tensile stress acting in a direction tangential to the circumference is called circumferential or hoop stress.
(b) Longitudinal Stress
A tensile stress acting in the direction of the axis is called longitudinal stress.