Abstract: Fractures were found in the header bolts of a pumped storage power station. According to bolt fracture analysis, fatigue cracks originated in the thread root were found in most of the bolts. Tip stress concentration induced by the source of cracks led to bolt fracture. To analyze the cause of bolt fracture, the diameter of the bolt was calculated and checked. It was found that the bolt diameter was small when the preloaded condition of the bolts was satisfied, and the fatigue strength calculation safety factor was small as well, which would lead to fatigue damage. Increasing the bolt diameter could not only meet the bolt preloading requirement, and also meet the requirement of bolt fatigue design.

Key words: pumped storage power station, header bolt, fracture, fatigue, preloaded safety factor, safety factor of fatigue strength