In the energy sector two checks determine plant availability: the actual load on the bolts in structural joints and the remaining wall thickness of piping and steam generators. Both are carried out by the ultrasonic method, both within extremely tight outage windows.
- ✓ Measurement of the bolt’s actual load, not of the applied torque
- ✓ Continuous and remote monitoring with the 4-channel MultiMax
- ✓ Automatic temperature compensation on the monitored joints
- ✓ Thickness on small-diameter tubes with dedicated probes
- ✓ Scan mode to find the thinnest point during the outage
- ✓ Data archived and reported with DakMaster™
Tightening a bolt to torque means measuring friction, not load. Much of the applied torque is consumed between the thread and the underside of the head, and the share that actually becomes clamping force varies with the surface condition, the lubrication and the assembly sequence. On a structural joint of a wind turbine, where the load is cyclic and the consequence of loosening cannot be recovered, that uncertainty is not acceptable.
The ultrasonic method, by contrast, measures the elastic elongation of the bolt: the time of flight of the pulse changes in proportion to the deformation, and from this the applied load is derived. It is a direct measurement of the quantity that matters. With the Dakota MultiMax the same measurement can be made continuous and read remotely, with automatic temperature compensation, on joints that have to stay under control over time.
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The second front is the thermal-hydraulic one. Steam piping, superheaters and economisers thin through erosion and oxidation on the flue gas side, and the useful window for measuring them is the scheduled outage. Here speed of execution counts as much as accuracy.
The application cases of the sector
| Application case | What is measured |
|---|---|
| Bolt tension in wind turbines | Actual load on tower joints, section flanges and blade root connections |
| Piping and steam generators | Remaining wall thickness of tubes, headers and membrane walls |
| Power plant inspections during outages | Extensive campaigns within limited time windows |
Torque or elongation: the difference in practice
The torque wrench checks what the operator applies; the ultrasonic method checks what the bolt actually undergoes.
- The measurement is repeatable over time: the same bolt is re-checked months later
- It detects loosening in service, which the assembly torque cannot predict
- The BT1-DL works in the field, the BT2-DL on the bench across several channels
- The MultiMax makes the measurement continuous and readable remotely from a PC
The MultiMax has neither keypad nor display: it is configured and read exclusively through the MultiUI software.
Dakota NDT instruments for the sector
| Instrument | When it is the right choice |
|---|---|
| Dakota BT1-DL MiniMax | Tightening checks in the field, at height, with an integrated data logger |
| Dakota BT2-DL Max II | Multi-channel benchtop version: simultaneous measurement on several bolts |
| Dakota MultiMax | Continuous and remote monitoring on 4 channels, stackable modules |
| Dakota CMX2-DL | Thickness on piping and headers, with A-Scan to validate the reading |
| Dakota CMX10-DL | Outage campaigns: six modes, colour A-Scan, flaw prove-up |
| Dakota MX1-DL | Large-scale grid mappings with a 4 GB data logger |
Reference standards
- ASME PCC-1 — assembly of pressure boundary bolted flange joints
- EN 14127 — ultrasonic thickness measurement
- ASTM E797 — thickness measurement by the contact method
- EN 15317 — verification of thickness measuring equipment
- EN ISO 9712 — qualification of NDT personnel
Frequently asked questions
Because it measures torque, not load. A substantial part of the applied torque is absorbed by friction between the thread and the underside of the head, and that share varies with lubrication, surface condition and tightening sequence. The ultrasonic method measures the elongation of the bolt, that is the elastic deformation from which the load is derived directly.
Yes, and it is one of the advantages of the method. If the reference length of the unloaded bolt is known, the measurement can be repeated after an interval on the same element to check whether the load has dropped. It is the way to detect loosening in service, which a torque check cannot reveal reliably.
Yes: it is a 4-channel multiplexed monitor designed for continuous measurement and remote reading, with automatic temperature compensation. It has no onboard controls, however: configuration and reading take place exclusively through the MultiUI software on a Windows PC.
You need a probe with a contact face suited to the curvature: on small diameters a transducer that is too large does not seat and the coupling turns out insufficient. There are small-diameter dual element probes dedicated to this use; tell us the diameter and the material and we will point you to the right transducer.
For tightening checks or a measurement campaign during an outage, write to us stating the type of joint or circuit and the time available.
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.
Some images on this website have been intentionally generated using Artificial Intelligence (AI). This is because, for many applications and projects, it is not possible to disclose photographs of the installation or of the actual system due to confidentiality agreements, confidentiality clauses and non-disclosure agreements (NDAs).