Wind turbines: accurately measure tightening tension

France-based TRAXX has developed the TRAXX-M2 solution , which accurately measures bolt tension in wind turbines, and many other areas, using ultrasonic sensors and software analysis, to help maintain the good load and good tightening of the screwed assemblies. The TRAXX-M2 solution can also digitally track bolts individually throughout their life, helping to ensure that each bolt remains at its optimal tension over the long term.

Although essential to product safety and reliability, correct bolt tension is difficult to achieve using traditional torque-based methods. And, as wind turbines continue to grow 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 tension crucial. A single loose bolt can trigger a domino effect that, in the worst case, could cause the entire wind turbine to fail.

The TRAXX-M2 system measures the length of the bolt as it extends in response to the application of tightening tension. These values are converted into precise tightening force. During the process of tensioning the assembly bolts, the operator observes the live data on the screen and stops applying load once the desired tension is reached. Once in service, measurement of 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 on the material properties of the bolt batch. By combining these three values, it is possible to measure and calculate the actual tightening force.

Accurate to within 3%, TRAXX R&D claims that the TRAXX-M2 system offers a superior advantage over torque methods where error tolerance can reach up to 50%. Compared to existing measurement solutions, the TRAXX-M2 can be implemented at a fraction of the cost and used directly on standard bolts.

The TRAXX-M2 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 complete TRAXX-M2 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 service and maintenance schedule. No pretreatment of bolts is required.