Wind Turbine Tower Bolts: Key Points About Wind Turbine Tower Bolts

　　Wind turbine tower bolts: Wind power boasts mature technology, high reliability, low costs, and significant economies of scale. It can operate either on or off the grid and is one of China’s fastest‑growing new‑energy technologies. The tower serves as a critical support structure for wind turbines. To ensure cost‑effectiveness in manufacturing, transportation, and installation, towers are typically divided into several sections, with adjacent sections joined by wind turbine tower bolts.

　　Wind turbine tower bolts typically use 10.9-grade high-strength bolts, which are manufactured by thread rolling. High-strength bolts used for connecting tower sections, subjected to harsh operating conditions and cyclic loading, are prone to developing significant localized strain and stress at the threads, placing the bolts in a fatigue‑prone stress state.

　　The factors influencing the fatigue life of wind turbine tower‑column bolts can generally be categorized into three aspects: stress conditions, manufacturing factors, and service environment. Stress conditions arise from stress concentrations and the mean stress amplitude during bolted connections. Manufacturing factors encompass the purity and strength of the raw materials, the heat‑treatment process of the bolts, the thread‑forming methods, and the corrosion‑protection measures employed. The service environment affects bolt fatigue life primarily through corrosive media and ambient temperature. These factors are interrelated and mutually influential; therefore, their combined effects must be comprehensively considered when assessing bolt fatigue life.

　　10.9-grade high-strength wind turbine tower bolts are typically manufactured from 42CrMo steel; their threads are rolled after heat treatment, and the bolt surfaces undergo Dacromet anti-corrosion coating following fabrication. During unit operation, tower‑to‑tower connection bolts are subjected to cyclic loading, making the stress state of the bolts a critical factor influencing their fatigue life.

　　In China, tower flanges are machined on CNC machine tools with extremely high precision, ensuring that the bolt‑mounting holes in the wind turbine tower meet the design specifications outlined in the drawings, thereby effectively controlling eccentricity and preventing forced assembly during the bolting process.

　　Furthermore, after the tower sections have been lifted into place, the bolts of the wind turbine tower should be pre-tensioned in a diagonal sequence to ensure that the pre‑load is evenly distributed throughout the bolt‑installation process. This approach allows the stress concentration factor at the tower‑to‑tower connection bolts to remain within the limits specified by relevant codes under normal operating conditions. At present, megawatt‑class wind turbines typically feature relatively tall towers, with heights around 80 m, and large‑diameter tower segments—commonly 4.2 m in diameter at the base. However, when these tower segments are welded to the connecting flanges, the heat‑affected zone can compromise the flatness of the flange surfaces to some extent. Consequently, in many projects, a small gap inevitably remains between the mating faces of the flanges after the tower segments have been hoisted into position.

　　The root cause of fatigue failure in wind turbine tower‑section bolts is the accumulation of damage. To ensure the bolt’s fatigue life, the stress amplitude experienced by in-service bolts should not exceed the allowable stress amplitude specified in the bolt’s design. Taking a reverse‑balance flange used in a particular project as an example, the effect of flange clearance on bolt fatigue life was evaluated by calculating the bolt’s stress amplitude and comparing the results.

　　Ningbo Xuanli High Strength Fasteners Co., Ltd. specializes in wind power anchor plates, high-strength prestressed anchor bolts for wind turbines, blade connection bolts for wind turbines, foundation anchor bolt cages for wind turbines, and tower bolts for wind turbines. Since its establishment, the company has supplied a large number of high-quality wind turbine anchor bolt cage products for key new-energy wind power projects, supporting thousands of wind turbine units. Our products are distributed across nearly thirty provinces, municipalities, and autonomous regions nationwide. With excellent product quality and outstanding service, we have earned the trust of a wide range of customers. Domestically, numerous enterprises have established long-term, friendly business relationships with us, helping to build a strong reputation in China’s high-strength fastener industry for wind power. Adhering to the corporate mission of “creating premium products and putting customers first,” we are committed to providing even more customers with superior products and services.