Torque verification is vitally important…
If you ever doubt that verifying the correct residual load in each and every bolt is key in industrial bolting applications, read on.
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 point to incorrect bolt installation as the root cause of the collapse and government accident investigation authority SHK says there are clear signs of fatigue and corrosion at the joint between the bottom and second section of the tower.
Low pretension force in the joint
“The bolts that 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 says the cause of the fatigue was low pretension force in the joint.
It says the reason for not achieving the required standard is “due to 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 the 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, at the top of the tower, where the 55 ton nacelle and blades are located.
Incorrect tensioning was again the main suspect.
Even with inexperienced operators, if the TORQ-COMM Commander system from ULTRA-TORQ was in use in either of these cases, the bolt tension and torque would be verifiable at installation, and catastrophic failures avoided.
Make sure this doesn’t happen on your job site. For advice on the best tools for safety and accuracy in your application, give us a call today.