Fatigue fracture failure analysis and improvement research of main steam valve bolts in a 300 MW thermal power plant

This paper presents a fatigue fracture failure analysis and corresponding improvement measures for main valve bolts in a 300 MW thermal power plant. The investigation begins with on-site inspections and the collection of fractured bolts, followed by visual examination and preliminary fracture analysis. Scanning electron microscopy (SEM) is then employed to observe the microstructure of the fracture surfaces, enabling the identification of fatigue crack initiation sites, propagation paths, and the ultimate fracture mechanisms. Concurrently, mechanical tests including hardness, tensile, and impact tests are conducted to assess whether the bolt materials meet the required design specifications. A detailed evaluation of the installation and service conditions–such as preload, operating temperature, vibration, and environmental corrosivity–is also performed to determine their potential influence on the fatigue life of the bolts. The experimental results indicate that the proposed approach ensures continuous improvement in solution quality, and the fitness value of the load capacity reduction factor gradually stabilizes upon application of the method. At this stage, an optimal solution is achieved, and the analytical approach proves both effective and highly accurate. It demonstrates enhanced precision in predicting potential fatigue crack locations, which can contribute significantly to improving the fatigue life and fracture toughness of the material. Based on the findings, targeted improvement measures are proposed to enhance the operational efficiency and reliability of the thermal power plant. The fatigue crack initiation and propagation mechanisms in main valve bolts are revealed through SEM fractography, with key failure origins identified. Comprehensive mechanical testing confirms the material properties of the bolts and pinpoints deviations from design specifications. Operational conditions, including preload, temperature, and vibration, are investigated to assess their impact on fatigue life. An optimized analytical method is proposed, which enhances the prediction accuracy of crack locations and contributes to improved fatigue resistance. Targeted improvement strategies are provided to enhance bolt reliability and overall power plant operational stability.