The connections of a wind tower work under permanent cyclic load. Torque tightening leaves an uncertainty that time amplifies; measuring the elongation says how hard each bolt is really pulling.
- ✓ Measurement of the actual load, not of the torque applied
- ✓ Check of uniformity across the whole flange ring
- ✓ Periodic re-checking of the same bolt over time
- ✓ Continuous monitoring, remote, with the 4-channel MultiMax
- ✓ Automatic temperature compensation
- ✓ Portable instrument for work in the nacelle and in the tower
A wind turbine transmits to the ground, through a handful of bolted connections, all the load the rotor gathers from the wind. The flanges joining the tower sections, the connection to the foundation and the ring at the blade root are the points where that force concentrates, and they are also the points where insufficient or uneven tightening turns into a structural problem.
The difficulty is that torque tightening does not say what load was actually applied: much of the torque is consumed in friction, and the useful share varies with lubrication and with the condition of the thread. On a ring of dozens of bolts this produces an uneven distribution that no torque check can capture, because reapplying the wrench to an already tightened bolt says very little.
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Ultrasonic measurement of the elongation returns the load directly. And since the reference length stays stored, the same bolt can be re-checked months later to see whether the load has dropped: it is the way to detect a loosening in service before it becomes visible by any other means.
The connections to keep under watch
| Connection | Why it is critical |
|---|---|
| Connection to the foundation | It transfers the entire load of the machine to the ground |
| Flanges between tower sections | Numerous rings, stressed in cyclic bending |
| Blade root and bearing | Rotating and variable load, difficult access |
| Nacelle connection | It carries large masses at height |
Periodic checking or continuous monitoring
On a machine up in the air, every climb costs. Hence the difference between the two possible strategies.
- Periodic checking with the portable BT1-DL is done during scheduled maintenance, bolt by bolt
- Continuous monitoring with the MultiMax leaves the sensors installed and reads remotely, without climbing
- The MultiMax handles 4 multiplexed channels and the modules stack to follow more bolts
- Automatic temperature compensation is essential on an exposed structure
The MultiMax has no on-board controls: it is configured and read through the MultiUI software.
Recommended instruments
| Instrument | Why in this application |
|---|---|
| Dakota BT1-DL MiniMax | Portable with data logger: the check at height, during maintenance |
| Dakota MultiMax | Continuous remote monitoring, 4 channels and stackable modules |
| Dakota BT2-DL Max II | Multi-channel benchtop for the preparation and calibration of the bolts |
| Bolt tension transducers | Probes dedicated to the measurement of the elongation |
Frequently asked questions
Yes, and that is why the method is used in this sector. Ultrasonic measurement reads the elongation of the bolt in the state it is in, without touching the tightening. If the reference length with the bolt unloaded is known, the value read gives the load directly.
It cuts the climbs devoted to checking the tightening, not every maintenance activity. With the MultiMax the sensors stay installed on the monitored connections and the readings are taken remotely through MultiUI: the climb is for installation and for the work itself, not for reading a value.
Yes: the speed of sound in steel varies with temperature, and on an exposed structure the swings are wide. Without correction the thermal variation would be read as a variation in load. The MultiMax has automatic compensation built in for exactly this reason.
Back to Energy and Renewables. For tightening control on your wind farm, write to us giving the type of connection, the bolt diameter and whether you prefer periodic checking or continuous monitoring.
Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
The information contained on this web page is provided for information purposes only. Although it has been compiled with the utmost care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.
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