A cylindrical steel tank contains a fluid under pressure. The ultimate shear strength of the steel is 300 MPa and a factor of safety of 4 is required. (E = 200 GPa; ν = 0.3).

The fluid pressure must be carefully controlled to ensure that the shear stress in the cylinder does not exceed the allowable shear stress limit. To monitor the tank, a strain gage records the longitudinal strain in the tank. Determine the critical strain gage reading that must not be exceeded for safe operation of the tank.