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Bolt tightening offshore: a crucial consideration

The Tin Man in the Wizard of Oz fretted over his joints, and wind turbines have the same problem. They need to be assembled offshore and maintenance of the joints is critical where a 20+ year life expectancy under the buffeting of winter seas and gusting storms is normal. The assembly is subject to prying forces, vibration and continuous temperature variation in a highly corrosive atmosphere of salt spray, rain and UV. Intellifast presents an illuminating despatch from the frontline of the wind energy arena…

Bolts are used to anchor the tower, for course assembly, and the nacelle. Many of these bolts are tightened close to yield. Each blade is attached to the hub with a large number of studs per blade. Any engineer who has recently experienced the snapping of a bolt or a stud shearing, the time lost in extracting and replacement and the anxiety over what caused them, has an interest in re-visiting the issues and what can be done to avoid it in the future. It is not the cost of the bolt or stud, it is the symmetry of the joint tightening that has been disturbed, the shock load immediately applied to the adjacent bolts and possible unzipping, and the time and expense of replacement.

As turbines move further offshore maintenance of these valuable assets and taking precautions to avoid failure gain in relative importance. Increases in unit size from 2 to 6 and now perhaps 10 or 12 MW unit size are favoured by the economics and accentuate the problems. These units will be located in waters notorious for their weather and difficulty of access. The bolt sizes have increased from the familiar M30 and M36 to M42 and M64.


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