Wind turbine collapse in Victoria, Australia

[FacEngrPE]

I am going to offer a different theory of failure, based on some knowledge of slewing ring bearings, and this enlarged clip of the top of the mast, which looks like it is still circular. This indicates (to me) that the mast tube did not fail in buckling.

Slewing bearings have very exacting bolt tension requirements. They also have periodic re-tightening requirements. Low bolt tension can increase the risk of bolt fatigue failure.

Slewing rings have also been known to have internal failures which can lead to rapid disassembly.

By this theory the failure could have occurred at a time when the windspeed was much lower than the stated design speed,

 

[Tomfh]

and this enlarged clip of the top of the mast,

That's not the top of the tower. It's a mid height splice. See here, the top bit of the tower, which has come loose.


top

 

[SWComposites]

How the heck does that mid tower joint cleanly separate without any apparent deformation in the flanges?? Its almost as if some of the bolts were not installed and the others cleanly sheared off. Or the bolts were installed but the nuts were not installed, and the upper part just lifted right off.

 

[Tomfh]

Early friday knockoff maybe?

 

[TugboatEng]

The site recently has another accident caused by missing bolts...

Worker crushed and killed by wind turbine blade | WorkSafe Victoria

WorkSafe is reminding employers about the risks of lifting loads with cranes.

www.worksafe.vic.gov.au

And there is always this common theme: Priorities other than safety.

 

[FacEngrPE]

The large image rules out a slewing bearing problem. The buckling in the image could be either from unbalanced rotating load, or from impact with the ground. My opinion is that the flange bolts are a strong candidate for further examination.

I do not expect a wind turbine mast to be designed to survive the loading from a loss of blade, while rotating at design speed.

 

[LionelHutz]

I'd agree with investigating the bolts. I'm doubting that flange joint properly assembled would be the weakest part of the tower, especially to the point it comes apart that cleanly.

 

[TugboatEng]

Here is another collapsed turbine, separated at a flange with zero visible deformation of the flange.

Wind turbine collapses in unknown circumstances in Oklahoma

The operator stated that the site is secure, and the farm is operational. However, the windmill manufacturer started an investigation to establish the circumstances of the collapse.

www.notebookcheck.net

 

[SnTMan]

Hard to say, but looks like bolts again. From the pic it looks like flange and bolting is internal to the cylinder. A reverse flange.

 

[TugboatEng]

These things must be coming apart like a zipper. Is it possible to determine if the bolts were improperly tensioned considering every single one has broken? I guess they'll have to check the neighboring units.

 

[Sym P. le]

The material seems to be some type of composite given the ragged and fibrous torn edges, not to mention all the "crumbs" on the ground.

 

[TugboatEng]

I was more interested in this part of the photo.

Composite? Maybe that explains the bolt failures. Composites have compression limits that may not allow proper tensioning of steel fasteners.

 

[Tomfh]

The towers are generally steel. The blades (e.g. in the shattered image above) are generally fibreglass or similar.

The fact these ones fell apart at the bolted splice in light winds means there must be some major omission. Bolts missing or something.

 

[SWComposites]

Yep, towers are steel. The blades are fiberglass composite.

 

[TugboatEng]

We use portable HyTorc systems to draw down the bolts on our z-drives. There may be 40ish bolts in a flange, 30-36mm bolt diameter. The power pack often overheats during the tightening sequence which turns tightening into a 2 day process.

 

[TugboatEng]

Here is a normal appearing collapse.

Multiple Vestas turbine collapses keep major US wind farm offline | Recharge

Three wind turbines made by Danish manufacturer collapsed last year at Missouri wind farm owned by local utility Ameren

www.rechargenews.com

Buckled in the column, not separated at a flange.