Application Technology

Denmark-based R&D AS has developed the Bolt-Check solution, which accurately measures bolt tension within wind turbines, using ultrasonic sensors and software analysis, to help maintain the right tension of bolted joints.

Recently approved by the challenging DNV-GL independent certification process for bolt clamping verification, the Bolt-Check solution can also digitally track individual bolts over their lifetime, which helps ensure each bolt remains at its optimal tension.

Although essential to safety and product reliability, correct bolt tension is hard to achieve using the traditional torque and tension methods, and as wind turbines continue to increase in size, it is more important than ever to maintain the integrity of the bolted joints in these structures. A wind turbine consists of thousands of different sized bolts, making correct bolt tensioning critical. One loose bolt can trigger a domino effect that, at worst, could result in the failure of the entire turbine.

The Bolt-Check system measures the length of the bolt as it lengthens in response to the application of load – torque or tension. These values are converted into accurate clamping force. During the bolt tensioning process at the assembly level, the operator observes the data live on the screen and stops applying load once the desired tension has been achieved. Once in service, measurement of the bolt tension is possible without the need to loosen the bolts. This is because the system uses ultrasonic and mechanical length measurements, as well as information about the material properties of the bolt batch. Combining these three values, makes it possible to measure and calculate the actual clamping force.

Accurate to within 5%, R&D states the Bolt-Check system offers a superior advantage over traditional torque and tension methods, for which error tolerance can be as much as 30%. Compared to existing measurement solutions, Bolt-Check can be implemented at a fraction of the price and used directly on standard bolts.

The Bolt-Check system can be used when installing new bolts and when evaluating existing bolts – as part of determining the lifespan of wind turbines. As part of the full Bolt-Check system, a unique traceability tag is added to each bolt, supporting pre-failure diagnosis and traceability, including the location of each bolt, as well as its schedule of service and maintenance. No pre-treatment of bolts is required.