A cylindrical steam boiler shell is riveted in 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 800 kN/m2 if the ultimate tensile stress of the material used is 600MN/m2. And the efficiency of the longitudinal joint is 70 percent determine the factor of safety?