Subject: Machine Design -I

Topic: Curved beams and Thin cylinder

Difficulty: Medium

Thin cylinder:

• Cylinder is considered thin when the ratio of its inner diameter to the wall thickness is more than 15.
• Boiler shells, pipes, tubes, and storage tanks are treated as thin cylinders.
• There are two principal stresses in thin cylinder, the circumferential or tangential stress and longitudinal stress.
• It is assumed that the stresses are uniformly distributed over the wall thickness.
• Considering equilibrium of forces acting on the half portion of cylinder of unit length (Ref fig a).

Where,

Pi = internal pressure (MPa),

Di = internal diameter of cylinder (mm)

t = cylinder wall thickness (mm)

• Considering equilibrium of forces in the longitudinal direction (Ref fig b)

• It is observed that the circumferential stress is twice the longitudinal stress.