Failure analysis and treatment of sealing gland bolts for bulb turbine expansion joints

Abstract The sealing gland and sealing strip are the main means of waterproofing the expansion joint of the bulb turbine. Fracture Failure of the sealing gland bolts will lead to sealing failure, causing water leakage and even flooding of the plant accident. Aiming at the fracture failure of sealing gland bolts for bulb turbine expansion joints, samples were taken from the fracture A2-70 stainless steel bolts and 8.8 grade high-strength carbon steel bolts. Combined with physical and chemical inspection, vibration testing and finite element simulation analysis, the reasons for the fracture of sealing gland bolts were studied, and corresponding preventive measures were proposed. Research results show that bolt fracture failure is not caused by quality problems of the bolt itself, but by alternating unidirectional plane bending fatigue loads with low stress levels. The fracture failure of the gland bolts can be prevented by increasing the fatigue strength of the gland bolts, adjusting the on-cam relationship to reduce unit vibration, installing spherical washers, and adding sealing gland jack screw to reduce the impact of unit vibration on the sealing gland bolts. The research methods and results can provide scientific basis and reference for the operation and maintenance of connecting bolts of important components of hydroelectric projects, including expansion joint gland bolts.