A cylindrical steam boiler shell is of riveted construction

A cylindrical steam boiler shell is of riveted construction.  It is made from plates 18mm thick, and has a diameter of 1.8m.  Calculate the circumferential and longitudinal stresses in the plates when the internal pressure is 800KN/m2.

If the ultimate tensile stress of the material used is 600MN/m2, and the efficiency of the longitudinal joint is 70 per cent, determine the factor of safety?