Selection of Bolt Preload for Impulsively Loaded Vessels

Guidance for the appropriate preload for bolted joints is well established for static pressure loading as well as cyclic loading. The goal for bolt-preload selection in these cases is generally leak prevention, alleviation of bolt loosening, and minimization of fatigue loading of the closure bolts. For impulsively loaded containment vessels, such as those governed by the rules of ASME Code Case 2564 in Section VIII, Div. 3, much less is known regarding appropriate bolt-preload selection. In this paper, a simplified, upper-bound bolt-preload methodology is developed to evaluate the role of bolt preload on peak bolt stress, including the effect of transient vessel motions. The simplified model for the bolted joint and vessel is solved in closed form for exponential pressure-pulse loading on the interior of a spherical containment vessel. Detailed finite element calculations are also performed using a refined model to more precisely examine the role of bolt preload. Comparisons of the approximate bolt-preload methodology with the detailed finite element results are then presented, along with comparisons to a lower-bound solution reported earlier. It is shown that the peak bolt stress predicted by the detailed finite element model is bounded from above and below by the simplified solutions. Implications on the role of bolt preload on peak dynamic bolt stress are given for sudden pressure-pulse loading. Goals and requirements for selecting bolt preload for impulsively loaded vessels are briefly discussed.