Patent Application
20190271350
This application claims priority to European Application no. 18159519.0, having a filing date of Mar. 1, 2018, the entire contents of which are hereby incorporated by reference.
The embodiments of the invention concern a method for corrosion protection in bolt holes of a wind turbine and a wind turbine.
Wind turbines are often installed offshore or in onshore sites with humid climate, like, for example, northern Europe. In such environments, water may cause corrosion in structures of the wind turbines. In particular, bolt holes are susceptible to such corrosion, which may result in cracking of wind turbine components, which consequently have to be replaced. Modern wind turbines may comprise 1000 or more bolt holes which thus need corrosion protection measures to withstand the adversary conditions at their installation site. In particular, this corrosion protection is supposed to be efficient for the whole lifetime of the wind turbine.
To provide such corrosion protection, products based on oil and wax were proposed to protect bolt holes from corrosion. However, these materials provide no long-term solution. Another proposal was to use thermal spray metallization, which led to excessive temperature build-up in the bolt holes and thus cannot be applied.
In current wind turbines, paint coatings are used as corrosion protection. However, this solution has disadvantages. During production, the adhesion properties, for example due to low-quality sandblasting processes, are not sufficient. Additionally, uneven coating film formation in the bolt holes results in poor corrosion protection. All solutions using paint additionally suffer the disadvantage that they cannot resist impact from the bolt mounting process.
An aspect relates to providing reliable and easy-to-apply corrosion protection to bolt holes of a wind turbine.
In a method according to the embodiments of the invention, a sleeve made of a corrosion resistant metallic material is inserted into the bolt hole, preferably covering the whole length of the bolt hole walls, and is at least partly expanded using an expander tool, the sleeve being expanded to be fixed in the bolt hole.
While in most cases the sleeve will be covering the whole length of the bolt hole, thus fully protecting it, it is also conceivable to use sleeves that cover only part of the length of the bolt hole.
The sleeve, in particular, has a cylindrical form corresponding to the bolt hole, in particular such that the outer diameter of the sleeve at least essentially matches the diameter of the bolt hole. Using sleeves made of corrosion resistant metal or metal alloys, i.e. pure metal or alloy, in particular aluminium and/or zinc, ensures that a sufficient amount of corrosion resistant metal is applied for any full lifetime in a marine environment. A sleeve, for example an aluminium sleeve or a zinc sleeve, is inserted into a bolt hole for a wind turbine component and then expanded, such that is it fixated in the bolt hole.
The sleeve delivers appropriate corrosion protection for extended durability along with sufficient mechanical strength to resist impact from the bolt mounting process. This has up to now not been achievable with coating systems used in the state of the art. As the fixing of the sleeves in the bolt holes is easy to perform, significant savings in production time and also in material cost can be achieved, compared to solutions using paint or similar coatings.
The proposed method and corrosion protection as such is particularly suitable for blade bearings, but can, of course, also be applied to other, in particular larger and/or deeper bolt holes of a wind turbine.
Tests regarding the corrosion protection have been performed on bolt holes provided with a sleeve as described above. Salt spray testing according to ISO 9227 has been applied for 1440 hours, sea water immersion according to ISO 20340 method B has been applied for 4200 hours, corresponding to a C5 environment. A sleeve made of an aluminium alloy has been used. No corrosion was observed in the sleeve material or the bolt hole material, in this case and for most components of the wind turbine being steel.
As has additionally been shown, the sleeves fixed by expanding them in the bolt hole showed good adhesion with the bolt hole base material, in particular steel, resisting an axial force corresponding to more than 5 tons. The tests also showed that a sleeve thickness of 1.2 mm is sufficient to obtain the corrosion protection needed. In general, the sleeve may have a thickness of at least 1.2 mm, in particular 1.2 mm to 3 mm.
The aluminium alloy used in the tests also had a high ductility and was highly resistant to pitting corrosion.
Another advantage of the current embodiments of the invention is that expansion technology usable to fix the sleeve in a bolt hole is already known from other fields of technology, in particular in relation to pipe coolers and heat exchangers. In particular, so-called tube expanders may be used as expander tool. Pipe coolers and heat exchangers can be constructed by inserting cooling/heating pipes into drilled holes in two and-pieces. The pipes are mechanically fixed in the drilled holes by expanding the pipe with tube rolling equipment or the like. For example, an electrical or pneumatic roller machine having an expander mandrel can be used as tube expander. In this field of the art, the expanding method is widely used and stationary and handheld expander tools are commercially available worldwide. These tools can also be used as expander tools in the method according to the embodiments of the invention.
Preferably, at least the end parts of the sleeves, in particular extending over at least 20% of the sleeve, are expanded. However, in a more preferred embodiment, the sleeve is expanded over its whole length. In this manner, the best mechanical adherence is achieved. If, due to production issues, it is not possible to expand the sleeves over their whole length, it is preferred that the end parts of the sleeves are expanded, preferably the first 20 to 25% in each end of the sleeves. If, for example, a 200 mm deep bearing is used as a bolt hole, 40 to 50 mm from both sides of the sleeve may be expanded.
In another preferred embodiment, the sleeve protrudes from the bolt hole at at least one end, in particular both ends, to form a holding rim when the sleeve is expanded. In this manner, the axial influence of the bolts during the mounting thereof may be mitigated or avoided. During the expansion process, the protruding part may be crimped to form the holding rim or a protrusion may be formed by expanding material from the protruding part further than the inner diameter of the bolt hole. Such a holding rim may also be termed overhang or corbel.
The embodiments of the invention also comprises a wind turbine, comprising bolt holes for bolted connection between components, wherein at least a part of the bolt holes has a sleeve made of a corrosion resistant metallic material fixed therein by expanding, in particular using a method according to the embodiments of the invention, and preferably covering the whole length of the bolt holes. All embodiments and comments regarding the inventive method can also be applied to the wind turbine according to the embodiments of the invention, in particular the corrosion resistant metallic material comprising zinc and/or aluminium and/or the sleeve having a holding rim. It is noted at this point that the corrosion resistant metallic material may be an alloy or a single metal.
In a preferred embodiment, the sleeved bolt holes are used for connecting blade bearings to a hub. As already mentioned, the method is particularly suited for both bolted connections, since large forces occur at these components such that corrosion effects, in particular those leading to cracks, have to be avoided, which is achieved by the current embodiments of the invention.
As is often the case in wind turbines, the bolt hole walls may be made of steel. Corrosion protection is particularly important in marine applications, such that the wind turbine may preferably be an offshore wind turbine. However, the embodiments of the invention can also be advantageously applied in any humid onshore site.
Some embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, where in:
According to the method, as shown in
Optionally, the sleeve 5 may be chosen a bit longer than the length of the bolt hole 2 such that it protrudes over the bolt hole 2 at both ends, resulting in the forming of a holding rim 8 during the expanding process.
Finally,
Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18159519.0 | Mar 2018 | EP | regional |
