Watch a video about one of Gundersen Health System’s Envision® wind farm projects.
The photo on the left shows a wind turbine flange bolt, nut, and washer. The bolt is about 18 inches in length and weighs approximately 40 pounds. You may notice the pink color of the bolt which is a special coating that acts as a rust inhibitor and a dry lubricant for easier assembly. The photo on the right shows several of these bolts after assembly in a flanged joint on a turbine tower section. You can see in the photo that there are marks numbering each bolt and indicating the position of the nuts on the bolt. The technicians use this as a means to ensure proper tensioning of the bolts in the assembly.
Flange bolts are a critical component in the tower structure and ensure that the tower sections are properly clamped and that the tower will be stable. The nuts are run down onto the bolts from the top in this particular design. Since the bolts are so heavy and the proper torque required is so strong, special equipment must be used to fasten these joints. The bolt pattern is torqued several times throughout the assembly process to make sure that the bolts are stretched and have sufficient tension to provide the proper clamping force to the flange joint in the tower. Technicians will also verify these measurements at later intervals to ensure that the joints have not relaxed over time and that they are not compromised in other ways such as with accidental damage or from corrosion.
Flanged connections are an effective and proven way to connect sections of a wind turbine tower and should hold for decades with the proper design and inspection. Bolts and other heavy components must be handled with appropriate methods to prevent injuries during assembly or possibly fatal accidents if dropped while lifting to their point of use. Adherence to safety procedures and codes during construction needs to be a priority for everyone involved.