BOLTING & FASTENINGS FEATURE SPONSOR
A MEASURED APPROACH TO REDUCING COSTS: A SIMPLE SOLUTION
OEMs, operators and service providers are all in search of greater reliability and reduced costs. But is it possible there could be a simple solution right under their noses that could save them millions of pounds just by adopting a basic engineering principle – accurately measure what you are doing?
COMPLEX STRUCTURES Wind turbine assemblies are complex structures. A typical 2.3 MW turbine will have nine major bolted joints in its construction with approximately 1,000 bolts in the complete assembly. The most obvious and visible bolted joints are the main turbine blades connecting to the blade bearing and bearing to hub, but other critical joints include the bearing to shaft joint, base frame, gear stays, the yaw bearing, as well as tower flanges and foundations.
Many of these joints are subject to complex
working loads and their operational reliability is a critical factor in reducing
expensive downtime – fatigue and vibration are cited as the most common factors that contribute to failures. Regular maintenance checks are also very time consuming, and in offshore operations the challenges are even more acute.
ASSUMPTION
The common mistake is to assume that there is a reliable correlation between the tightening force being applied, the torque, and the tension being achieved – there isn’t!
Three basic factors make up the science of achieving bolted joint integrity and reliability - the right joint design, the right component quality and the correct tension across the joint.
CHALLENGING TRADITION So how can measurement play a major role in improving reliability and driving down the costs commonly associated with bolted joints? When bolts are tightened up using traditional practices what is being measured is the force being applied to do the tightening – the torque.
What is not measured at all is the corresponding tension that is being achieved across the bolted joint and it is this factor that is absolutely critical to the reliability and integrity of the joint.
The design and quality are factors that are both measured, but the tension across the joint rarely is. So it’s hardly surprising that research has consistently shown that around 90% of all bolted joint failures are caused by insufficient tension at installation.
One simple solution is to employ fasteners which have measurement technology built in to them. Fasteners that can accurately measure and maintain the correct tension throughout the life of the joint. The right design tension can then be achieved at installation and the resultant correct clamping force across the joint will combat the effects of
vibration loosening and fatigue failure.
PARALLEL LEARNING The theory of the science may seem convincing enough, but is there any ‘parallel learning’ that can be explored from another sector which evidences the benefits and adds weight to the argument in favour of using a measured approach?
The slew bearing of a pedestal crane is a bolted joint which
almost directly parallels the dynamics of key joints in a wind turbine. It is the single most important connection in the entire crane assembly and the performance of the crane depends on the critical load path through this bearing.
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www.windenergynetwork.co.uk
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