How to Protect Wind Turbine Foundation Bolts from the Effects of Corrosion

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A standard 1.5-megawatt wind turbine stands over 320 feet tall (including blades) and weighs over 164 tons. Protecting wind turbine foundation bolts from the effects of corrosion is of utmost importance.
Wind turbines are specifically designed to be exposed to the worst weather on the planet.
 
A lot is written about the design and maintenance of turbine components–products to reduce wear and tear in the gears, how to control the atmosphere in the nacelle and tower to minimize corrosion, coating systems for the structure and blades–the list of ASTM and ISO standards that apply to the design and manufacture of these complex structures is much longer than my arm.
 

However, there is very little information available regarding the maintenance of wind turbine foundation bolts, also known as anchor bolts. Wind turbine foundations are a big deal.

A standard 1.5 megawatt wind turbine tower is well over 200 feet high (with its blades making it more than 320 feet), supporting a combined weight of 56 tons for the nacelle and 36 tons for the blade assembly. The tower itself weighs another 72 tons. The entire 164+ tons is anchored to its foundation by a series of bolts set in concrete.
 
Once the foundation is complete, the first section of the tower is lowered on to the bolts and secured, then the rest of the turbine is assembled above. The bolts have to be tensioned accurately to prevent any movement on the base as the tower flexes in strong winds it is designed for, but still allow some stretch to reduce foundation deflections from the high wind loadings.

 

The condition of the bolts and nuts is critical to the long-term survival of the tower.

Bolt tension issues have been identified as a cause for failure in turbine collapses as have bolt failures from the effects of corrosion.

rusting corroded wind turbine foundation bolts

Yet many bolts are left exposed to the elements, with the result that corrosion rapidly occurs.

Proprietary solutions exist for post-construction remediation of corrosion damage to exposed bolts, including tape wraps, grease and bolt caps, but all suffer from limitations that require frequent maintenance or replacement to prevent corrosion damage to the turbine anchors. If the nuts and threads corrode, retensioning anchor bolts properly is impossible.

The entire turbine structure relies on a few relatively small nuts to ensure it is firmly fixed to the anchor bolts, yet it is left to the operator to ensure they get the protection they need.

We think protection of these nuts is pretty important. Turbine towers do not collapse very frequently and, because they tend to be off the beaten track, injuries from such collapses are rare but the cost of replacement runs into millions and the constant vigilance that is required to maintain the bolts is wasteful and unnecessary.

 

The Enviropeel solution to wind turbine foundation bolt corrosion is simple.

Anchor bolts can vary in length but the exposed threads are always several inches long, so providing the correct size of bolt cap can be a problem. Because Enviropeel bolt applications will fit any size or shape of bolt, it provides a straightforward, one-size fits all solution, but this is not its only advantage over bolt caps.

Bolt caps have to stay in position to work, they usually have some kind of friction fit mechanism to maintain their seal with the base but this is not always effective. Because Enviropeel is spray applied, it moulds itself around every thread making it impossible to dislodge yet easy to remove, if required, by simply screwing it off.

And, of course, Enviropeel contains its own active inhibitors so, if corrosion is already present in the bolts, it not only prevents further deterioration but it will also condition the nuts and threads so that they can easily be adjusted for maintenance.

Compare this with protection using a wrapping system … as long as the wrap stays intact, it will provide a barrier to water ingress but nothing else. And, it cannot be removed for inspection without having to be completely replaced whereas, with Enviropeel, it can be removed and replaced.

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