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Failure Of Bolts On Wind Turbines

After a bolt failure incident at the Lemnhult Wind Farm in Sweden in 2015 caused the collapse of a turbine, the remaining 31 wind turbines were taken out of operation until they could be checked.

What caused the Wind Turbine to collapse? Could this have been prevented, and could costly downtime have been avoided? In this article, I look at the points raised in the investigation following the incident, and how with the support from market leaders in joint integrity and flange management, you can ensure that everything is being done to prevent such incidents from occurring in the future.

An avoidable incident?

In 2015, a 185 metre high wind turbine located in the Lemnhult wind farm in Sweden collapsed when the bolts in the tower’s flange joint, containing one hundred M64 bolts, failed. (1.)

In the report by the Swedish Accident Investigation Authority, Statens Haverikomission (SHK), it was noted that an amount of gear oil and hydraulic oil ran out into the nearby area when the machine casing hit the ground. (2.) After the incident, the remaining 31 wind turbines within the Lemnhult wind farm were taken out of operation until they could be investigated and safety checked.

The Investigation

On investigation into the incident, there were a worrying number of issues that came to light that were considered as contributing factors to the overall failure of the turbine, including:

  • The torque tooling was not properly maintained
  • The bolts failed in fatigue, with the root cause of fatigue being insufficient bolt tension.
  • There was no checks completed to check that the correct tension had been achieved.
  • The equipment operator wasn’t adequately qualified and was inexperienced.
  • The windfarm had problems in the past regarding broken and loose bolts that weren’t reported to the authorities.

Was the incident avoidable? If the above issues had not been present then the chance of such an incident occurring would have been substantially lower.

Lessons Learned

With wind power rapidly becoming a large player both onshore and offshore, the global wind market is expected to return to “dramatic” growth in 2019 after a “flat” 2018. (3)  A recent market forecast for 2018-2022 by the Global Wind Energy Council suggests a steady increase, with a cumulative installed capacity in 2022 surpassing 800GW (5).With this in mind, it is imperative that more steps are being taken in terms of compliance and regulation, to ensure that failure of bolts on wind turbines is reduced, whilst decreasing the risk of such an occurrence in the future.

Basic Technical Training

The introduction of compulsory BTT Certifications from the Global Wind Organisation (GWO) for technicians working for GWO Member companies and their suppliers is another step forward in ensuring that all Turbine Technicians are competent and suitably qualified to carry out work on turbines. (4) Without the BTT qualification and relevant knowledge, employees will not be able to commence working on the turbines.

Maintenance of Equipment

Any tooling used on site must meet with the manufacturer’s recommendations of Calibration and Servicing. The maintenance of equipment is not only imperative in ensuring the tooling is fit for purpose, but also minimises risk of the tooling breaking down on site which creates further problems while work has to stop for the tool to either be repaired or replaced.

Calibrating of tooling ensures that the equipment is producing output to the specified level.

Joint Integrity Documentation and Records

Data capture and analysis has never been more prominent in the industry, and the recording of information on flange management and bolted joints creates not only a documented process but increases the efficacy of a leak-free joint.

Solutions under one roof

HTL Group have proudly been providing their 100% British Made Torque & Tension equipment to a variety of industries including wind, for over two decades. HTL deliver a wide range of value added services including the industry’s most innovative calibration service; i-calibrate, testing & certification, joint integrity software and asset management. HTL are also an approved provider of the GWO BTT training course at our dedicated Training Centre of Excellence in Cramlington.

With a plethora of solutions under one roof, HTL are positioned to assist in all aspects of joint integrity and flange management.

Interested in finding out more? To discuss how HTL can support you with controlled bolting solutions, contact me on, call +44 (0)1670 700 002, or visit our website by clicking here.


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One response to “Failure Of Bolts On Wind Turbines”

  1. Karlo lucic says:

    Importance of calibration, training, maintenance and documentation/traceability never stops.

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Karlo lucic says:

Importance of calibration, training, maintenance and documentation/traceability never stops.


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