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A SOBERING LESSON IN VERIFYING BOLT LOAD

image credit: Image courtesy of windaction.org
Jon Naylor's picture
Global Business Development Torq-Comm International Inc

25 years experience in technical sales and marketing in the power generation and renewable sectors with a specific focus upon industrial bolting application engineering and bespoke solutions.

  • Member since 2021
  • 2 items added with 396 views
  • Jul 12, 2021
  • 396 views

On December 24th 2015 a three-year-old wind turbine collapsed across a road at the Lemnhult wind farm in Sweden. The road was only for access and nobody was injured or killed but the image shows the devastation and provokes a sobering thought about what may have happened were the turbine in another location.

Swedish officials have pointed to incorrect bolt installation as the root cause of the collapse and Government accident investigation authority SHK said there were clear signs of fatigue and corrosion at the join between the bottom and second section of the tower.

“The bolts that had held together the joint had suffered from a fatigue process and the bolts could no longer withstand the loads of normal operation. The flange surfaces in the main wind direction showed signs of corrosion which most likely originated from the bolts.”

SHK said the cause of the fatigue was “the pre-tension force in the joint was too low”. It said the reason for not achieving the required standard “was due to the bolts, tower sections and tools not being protected from rain and snow during installation”. SHK added that the tools were not maintained properly and that the assembler who performed final torqueing of the bolts “had no previous experience” and “had not received the manufacturer’s internal training”.

Last year a turbine suffered a similar bolt failure at a wind farm in Hawaii, albeit at the top of the tower. Incorrect tensioning was again the main suspect.

So, be it torque or tension, verification that the bolts are tightened correctly is critical. Even with inexperienced operators, were the Torq-Comm Commander system in use in either of these cases, the bolt tightness would be guaranteed and the catastrophic failures completely avoided.

Jon Naylor's picture
Thank Jon for the Post!
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Jim Stack's picture
Jim Stack on Jul 12, 2021

Jon, The basic operation of installation is very important as you have shown. I would expect they have a yearly inspection system also in place that could have caught these problems before they failed. Remote sensors could also show problems before a complete failure. Where any of these inspection methods included for this wind farm? 

Jon Naylor's picture
Jon Naylor on Jul 12, 2021

Hi Jim, Thanks for your input and question. The disturbing truth is that the global wind industry has a major issue with bolted connections. In almost every case, wind turbines are bolted together during construction to a design specification. In this case the issue was identified as the contractor not being familiar with industrial bolting methods. Remote sensors are available but cost prohibitive I believe. The key to a reliable joint first time, every time is ensuring the correct torque or tension is applied to every bolt in the correct sequence. Experience is one way but process control and data collection devices are the future, immediately turning novices into experts and recording and safely storing data on every fastener. Supervisory personnel can also monitor bolting technicians real time, from anywhere in the world. Hope that helps.

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