0Longitudinal Stress: Consider now again the Hoop stresses figure and the vessel could be considered to have closed ends and contains a fluid under a gauge pressure p. Then the walls of the cylinder will have a longitudinal stress as well as a circumferential stress.
Total force on the end of the cylinder owing to internal pressure
= pressure x area
Area of metal resisting this force = pd.t. (approximately)
because pd is the circumference and this is multiplied by the wall thickness
