Siemens has decided to undertake a major repair and inspection operation covering 54 of its 3.6 MW turbine units installed off-shore. The work will require the removal of turbine blades in order to inspect or replace the pitch bearings.
All 54 machines at Centrica's Lynn and Inner Dowsing wind farm are affected as well as three other UK offshore wind farms at Burbo Bank, Gunfleet sands and Rhyl Flats. It is the continuation of a process that started in August last year when Siemens announced that it was going to perform a service campaign at the four wind farms. Part of the work was related to potential issues with the corrosion protection in the bolt holes of some pitch bearings of the 3.6 MW WTGs, which had been detected earlier on some land based machines.
As a precautionary measure, Siemens started carrying out preventive maintenance of all 3.6 MW turbines with similar pitch bearings of same type and age group. At the Burbo project, Siemens decided to exchange all pitch bearings in 2010. The fastest way to carry out this preventative maintenance was to temporarily take down the blades so the bearing replacement work could be performed on board a jack-up vessel. During the service campaign at the other three projects, it was concluded that a 100% reliable inspection of the possible extent of corrosion in the bolt holes of the pitch bearings was not possible on site. Any decisions on the possible need for removal of pitch bearings require inspection of a number of dismantled bearings under proper conditions.
Consequently, in addition to the pitch bearings removed from the Burbo project, Siemens removed one set of bearings at the Lynn / Inner Dowsing project for further metallurgical inspections in the laboratory. Originally it was expected that the replacement of pitch bearings would only be carried out at Burbo. However, as a result of the laboratory inspection of the Burbo pitch bearings and the one set of pitch bearings from Lynn / Inner Dowsing, Siemens has decided to replace all remaining 53 pitch bearings at Lynn / Inner Dowsing. This replacement work will be carried out in 2011.
As part of the 2011 campaign Siemens is also planning to remove a set of pitch bearings from the Gunfleet Sands project for further inspections. Depending on the outcome of these investigations, Siemens might also decide to exchange the pitch bearings at Gunfleet Sands and Rhyl Flats. Both projects feature the same blade and pitch bearing design, therefore one sample will be sufficient.
For more recent projects, the corrosion protection in the bolt holes has been upgraded and no maintenance will be required for any offshore projects besides Burbo, Lynn / Inner Dowsing, Gunfleet Sands and Rhyl Flats.
In a statement, Siemens emphasised that the work carried out in 2010 at Burbo was done solely as a precautionary measure and that there have been no incidents or reported damage at any of the four wind farms. The turbines have operated reliably and safely to date, and the only downtime experienced has been that used for preparation and execution of preventative maintenance.
•Siemens is not the first manufacturer whose experience confirms that off-shore wind is technically challenging, is to some extent being learned at sea, and cannot yet be considered a fully mature technology. In 2004 the world's largest WTG maker, Vestas, had to carry out extensive transformer and generator replacements at its Horns Rev wind farm, at the time the world's largest offshore facility, mainly owing to an underestimation of the aggressiveness of the open sea environment.