4. In a cylindrical vessel a pressure of 3MPA acts on a circular cover plate. The cover plate has a diameter of 480mm and is held in a position by twenty bolts of 26mm diameter, equally spaced around the rim. Ignoring primary creep but account for elasticity with E=210GPA and a secondary creep rate of 37.6 x 10-174h-1, where o is in MPa: Given that ( - 1) Determine 1. The initial tightening stress in the bolts in order that a safety factor of 1.6 is maintained after 8000hrs of creep relaxation at 45 C. 2. The time when the bolts should be re-tightened to prevent leakage around the plate.