Bolted-flange connected structure is widely used on Primary Equipment of Nuclear Power Plant and it is one of the most important assemblies of Primary Coolant Loop. Special attentions should be paid for the design and validation of this kind of structure for high risks of leakage and structure integrity of the equipment. In this paper, preload of manway bolt for Pressurizer of Nuclear Power Plant under hydrotest condition was calculated theoretically. Bolt-load distribution for the bolted-flange connected structure was simulated by Finite Element Analysis method with the above preload applied. Bolt load loss and asymmetric distribution during the test was presented resulting from the simulation for saddle-shaped manway flange. Assessment was carried out according to ASME in the aspect of stress in the bolt shank, pressure on the gasket and rotating angle of the flange (sealing verification) with the corrected preload applied. The simulation results were validated by 1:1 prototype test carrying out for the Pressurizer and they were consistent with the test results. The value of coefficient Ks for bolt preload design formula was confirmed by the test. Key aspects of influence on manway bolt preload design were summarized and full design formula as well as value of the design preload for hydrotest condition were given.

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