Improving Wind Farm Performance: A Guide to Monitoring Preload in Bolted Joints

Secure bolted joints are critical for the operation and safety of infrastructure but ensuring that these joints are tightened, and stay tightened, to the correct preload can be a challenging task. As wind turbines get bigger, in increasingly harsh environments or on floating platforms, bolted connections are reaching their capacity limits and are often complex to design, install, and maintain. 

Traditional methods for monitoring preload, such as using torque wrenches or ultrasonic measurement, can be time-consuming and inaccurate. Now, with the advancement of SMART technologies, it's possible to install sensors on the joint and monitor the preload remotely – transmitting data via a Cloud and reading it from a smartphone or computer dashboard. You can, for example, achieve total control of preload on MP-TP flange connections. 

In this feature, we will focus on the role of Nord-Lock Group’s SMART solutions, Superbolt Load-Sensing Tensioner (LST) and Superbolt Load-Sensing Flexnut (LSF), for monitoring bolted joints in the wind industry and how they can help to improve safety, efficiency, and performance of wind turbines. 


How SMART preload monitoring works

Superbolt LST is based on the well-known Superbolt Multi-Jackbolt Tensioner (MJT), with strain gauges installed around the lower section of the nut body to measure its expansion as preload increases or decreases. 

Companies interested in remote preload monitoring don’t need additional skills or specialist knowledge to use our products. The plug-and-play systems can be used by an operator with a handheld device to read out preload during installation/maintenance checks, then left installed to transmit data during the lifetime of the application. Using a wind turbine’s Wi-Fi, or radio networks via sim cards, preload data can be monitored from a laptop or mobile screen anywhere in the world. 

There are no limits to where you can install Superbolt LST, and Nord-Lock Group has the possibility to support customers all over the world - including the licensing to supervise offshore installations in person.


How to use preload data gathered by Superbolt LST/LSF

A key advantage is that Nord-Lock Group SMART solutions can collect and store large amounts of data, which can be analyzed to detect patterns and trends. 

1: Remote Monitoring: get live preload updates at intervals defined by you (as frequently as 100 times per second), which is especially useful for turbines located in remote or difficult-to-reach locations. Preload can be monitored in real time, on screen and from anywhere in the world. 

2: Predictive Maintenance: use the data to understand changes in preload over time, identify a potential failure and alert the maintenance team for preventive maintenance. 

3: Alerts and Notifications: setup automatic notifications when preload falls outside of a predefined range, enabling maintenance teams to act fast and prevent damage. 

4: Historical Analysis: alongside sea level data, wind speeds and other weather conditions – use the saved preload data to troubleshoot past maintenance incidents/discoveries. 

5: Research & Development: use the preload data and weather conditions to help with the planning of future windfarm developments, or for innovating newer turbine designs. 

Using this data can help you to have a better understanding of what happens in your bolted connections – that is not limited only to the wind industry says Peter Clausen, Nord-Lock Group Engineer 

Where to monitor preload 

There are few restrictions, and Superbolt LST/LSF can be used to monitor preload on most bolted connections inside the wind turbine. They’re commonly applied to flange connections in the MP-TP connection given the increasingly large forces tower bolts are subjected to, on the blade-to-hub bolts, yaw bearings, anchor bolts and more. 

"For sure it makes sense in the rotor blade connections where we see high dynamic loads over their lifetime. Using LST is perfect in any hard-to-reach areas where customers experience a lot of maintenance cost" adds Clausen.

More generally, this kind of IoT-based remote preload monitoring can be used in any industry where the use of bolted joints is critical for the operation and safety of the equipment. There is huge potential in other power generation industries, as well as oil and gas, construction, rail infrastructure, manufacturing and mining, to name a few. 


What are the advantages of using Superbolt LST/LSF? 

Accurate: torque checks tell you if a bolt is loose or not. SMART solutions give you accurate preload values within a range of ±5% (Superbolt LST). 

Secure: Based on Multi-Jackbolt Tensioners (MJTs), which were originally invented by Superbolt in 1984, your bolted joints can be tightened with high accuracy without requiring specialized skills or heavy tooling. 

Cost-effective: because ‘prevention is cheaper than the cure’. Superbolt LST and LSF can be spaced periodically around a critical flange connection, for example, and give you a reliable, updated view on the long-term structural integrity of your infrastructure. Use this to plan more efficient maintenance schedules. 

Scalable: test Nord-Lock Group’s SMART technologies in partnership with expert engineers. Prove the concept in a sample of your applications, then scale up to cover your most important assets. 

Profitable: extend the lifecycle of your windfarm operations, or other, with reliable structural monitoring. 

Non-invasive to the structure: most monitoring/measuring methods are invasive, but Superbolt LST leaves the bolted connection as it is, without destroying anything or altering the calculations. 

Easy-to-use: Nord-Lock Group SMART products are essentially plug-and-play solutions, and you can get full support anywhere in the world to get started with installation and monitoring. 

Continuous: LST & LSF are at work, even when you are not, the dynamic monitoring of loads avoids bolt fatigue and fracturing. 


Case Study: monitoring preload in the North Sea 

Watch Nord-Lock Group Engineer and offshore specialist, Peter Clausen, talk about the worldwide potential for remote preload monitoring, and a successful installation of Superbolt LST in the German North Sea: 

To conclude, using remote preload monitoring systems can expand the possibilities of structural maintenance and infrastructure design. Today, Nord-Lock Group’s SMART solutions are actively supporting the wind industry to improve safety, plan more efficient maintenance and improve the overall performance of turbines. These principles and our experience are applicable in industries worldwide.


So, if you're interested in implementing remote preload monitoring, read more about Superbolt Load-Sensing Tensioner and Superbolt Load-Sensing Flexnut or contact a Nord-Lock Group engineer today: 

Contact us