Wind Farm Accident—Wind Turbine Bolt Failure
In the vast Gobi Desert, a wind farm once experienced a thrilling accident: a wind turbine suddenly made a sharp tearing sound during operation, and then the wind blades fell to the ground from a height of 100 meters like a giant bird with broken wings.
Accident Analysis of Wind Turbine Bolt
The accident investigation revealed a regrettable truth – a key connecting wind turbine bolt between the hub and the main shaft broke first, triggering a chain reaction, causing the load on adjacent bolts to surge and break one after another.
Cause of the Wind Farm Accident
The inspection report of a professional organization noted that the fatigue crack in the wind turbine bolts that broke first had begun half a year prior. If this hidden danger had been discovered earlier, this costly accident could have been avoided.
Wind Turbine Anchor Bolts—Core Components in Wind Tower Construction
This case is a sharp reminder that in the wind power industry, people tend to focus on the towering towers and huge blades, but often ignore the small components that silently support the entire system. A bolt, a washer, a locating pin, they seem insignificant, but they maintain the safe operation of the entire wind turbine. Among them, wind turbine anchor bolts are the core load-bearing components connecting the tower and the foundation. Their performance directly determines whether the wind turbine can withstand strong winds, alternating loads and corrosion in harsh environments during its 20-25 year life cycle. These “invisible guardians” are made of high-strength alloy steel and run through the entire foundation structure. They transmit huge tensile force to the concrete foundation through the upper and lower anchor plates, keeping the concrete under pressure for a long time, avoiding cracks, and significantly improving the durability of the structure.
Anchor Bolt Used to Build the Wind Farm Safely
During the operation of wind turbines, the anchor cage system is subjected to multiple complex stresses: constant tension caused by the wind tower’s weight, alternating loads caused by the aerodynamic imbalance of the wind rotor, instantaneous overloads under extreme wind conditions, and chloride ion corrosion unique to the offshore environment. Under the combined effect of these factors, once the anchor bolt fails, it will cause the wind tower to tilt or even fall. Therefore, professional high-strength anchor providers need to not only be proficient in material science, but also have a deep understanding of wind turbine operation mechanics. Through strict quality control and innovative technology, they ensure that each anchor is reliable from production to service, building the first line of defense for wind farm safety.
Mechanical Properties And Evolution Of Anchor Bolts
The technological evolution of wind power anchor systems directly reflects the industry’s increasing demand for safety. At present, wind turbine foundations mainly use 2 connection methods: prestressed anchors and foundation rings or anchor plate. There are essential differences between the 2 in terms of structural design and stress characteristics:
Table: Comparison of foundation performance between foundation ring and prestressed anchor bolt
| Characteristic | Basic ring structure | Prestressed anchor structure |
|---|---|---|
| Connection | Steel cylinder buried in concrete | Anchor rod + upper and lower anchor plate combination |
| Stiffness transition | There are mutations and stress concentration | Continuous elasticity, no sudden change point |
| Concrete state | Local tensile stress area | Long-term pressure |
| Typical faults | Joint flooding and cavity formation | Anchor bolt breakage and corrosion |
| Maintenance Difficulty | Difficult to repair, grouting reinforcement is required | Replaceable single anchor bolt |
| Applicable models | Early low and medium power units | Large units above 5MW |
- Foundation ring structure: The load is transmitted through a steel cylinder embedded in concrete. There is a sudden change in stiffness at the junction of the rigid cylinder wall and the concrete foundation, which is prone to form a stress concentration area under long-term alternating loads. After several years of operation, many coastal wind farms have experienced grouting at the foundation ring joints. Surveys have shown that a broken zone has formed between the foundation ring and the concrete, and a cavity has formed at the lower flange, posing a serious safety hazard. To repair this type of damage, it is necessary to drill a hole obliquely downward on the foundation cap to the flange for epoxy grouting reinforcement, which is costly.
- Prestressed anchor bolt structure: It consists of an upper anchor plate, a lower anchor plate, a high-strength anchor rod and a PVC protective tube . The anchor rod is isolated from the concrete by the protective tube. Its core technology is to apply precise prestress to the anchor bolt, so that the concrete foundation is in a state of compression for a long time to avoid cracks. When the anchor rod is pulled, the load is evenly transferred to the concrete through the lower anchor plate. The entire system is a continuous elastic body with no stress mutation points. This structure eliminates the inherent defects of the foundation ring connection and has become the preferred solution for modern large wind turbines.
Steel Standard Developed for Wind Anchor Cage Foundation Bolts Manufacture
The technical specifications of modern wind anchor cage foundation bolts are highly standardized.
Taking the 130MW wind power project in Puge Wukeliangzi, Sichuan as an example, its anchor bolt components require the use of M42 specification 8.8 grade high-strength anchor rods made of 42CrMo alloy steel and 3945mm long; the upper and lower anchor plates are made of 40mm and 45mm thick Q345E steel plates respectively, ensuring low-temperature toughness of 410. Higher power units, such as the 6.25MW wind turbine of the Xuanhua Wind Hydrogen Storage Project, require 10.9 grade anchor bolts (tensile strength 1040MPa, yield strength 940MPa) and Q355NE /Q355ND anchor plates to adapt to more severe stress environments.
Features and Performance of Wind Tower Anchor Bolt
The performance parameters of anchor bolts directly determine the safety margin of the wind turbine:
- Tensile strength: 10.9 grade anchor bolts must reach 1040MPa or above, which is three times the strength of ordinary bolts.
- Fatigue life: high-quality anchor bolts must pass ≥ 2 million cycles of loading test (such as Nanjing Mancate products)
- Low temperature toughness: Anchor bolts used in cold areas must meet the -40 ℃ impact energy ≥ 60J (Akv value)
- Corrosion resistance: Need to pass 3000 hours of salt spray test, the offshore environment requirements are more stringent
Tensile Strength Upgrade – 12.9 Ultra-High-Strength Anchor Bolt
As the trend of wind turbines becoming larger accelerates, anchor bolt design faces new challenges. As the capacity of a single unit jumps from the mainstream 3MW to over 6MW, the number of anchor bolts has decreased (for example, a 6.25MW unit only requires 16 sets), but the load strength requirements for a single bolt have increased dramatically. This has prompted professional manufacturers to continuously break through the limits of materials and develop 12.9-grade ultra-high-strength anchor bolts (tensile strength 1220MPa), and improve corrosion resistance through nano-coating technology to support the development of the wind power industry towards deep sea and ultra-high altitude.
