EDF Walkway Wind Farm is located 4.5km east of Sedgefield, Durham. On 26th of September 2019, wind turbine T6 nacelle caught fire and burned out. Based on the number of fires occurring in wind turbines worldwide, a decision was taken by EDF and their insurers to carry out a detailed forensic analysis of the nacelle. In order to do this the nacelle would need to be lowered to ground level, and transported to a covered location.
Keltbray Decommissioning were appointed to make safe, and recover the fire damaged nacelle. Scope of works included:
- Phase 1 – Preparation of a dismantling options report.
- Phase 2 – Investigation and first access to Turbine T6.
- Phase 3 – Removal of blades
- Phase 4 – Recovery of nacelle and transport to storage facility
- Phase 5 – Removal of top tower section
Key challenges and solutions
Due to the condition of the fire damaged structure, this project would require a collaborative approach between:
- Keltbray Decommissioning – Principal Contractor
- Keltbray Lifting Services – Management and coordination of lifting operations
- WHP – Engineering Design Support
Technical Challenge 1 – Blade Removal
During the fire, one of the three blades had been damaged to the point of failure, and broke off and dropped to grade level. There was therefore, a high probability that the other two blades had been significantly weakened, which meant they could not be removed by conventional means (2 Crane lift).
Following comparative risk assessment of the various methodologies available for removal of the blades, it was decided that the safest method would be to use a High Reach Demolition Excavator fitted with a shear attachment. This would require the rotor locking pin to be inserted at nacelle level to pin the blades in position, to allow the machine to safely reduce the blades to an agreed length (removing circa 75% of their total mass).
Technical Challenge 2 – Design of Lifting Beam and Arrangement
Due to effects of the fire, there were some concerns around the condition of the main nacelle support steelwork and bearings, which would require investigation and verification prior to design and certification of suitability for lifting operations.
WHP working in collaboration with Keltbray Decommissioning and Keltbray Lifting Services, carried out a detailed review of the existing structure, this included:
- Structural analysis modelling
- NDT Testing
- Weight and COG analysis
Following completion of the activities above, a number of design development workshops where carried out by the Keltbray project team with a view to selecting the safest method of lifting the nacelle. It was decided that a bespoke lifting beam would be fabricated and installed on the underside of the machine base, and the nacelle would be lifted in a four point lift from the beam to the front rotor. WHP carried out the design of the lifting beam, lifting study report and issued a design certificate to cover both.
Technical Challenge 3 – Planning, Coordination and Execution of Lifting Operations
Following selection of lifting methodology, the next challenge would be the planning and coordination of the lift, which would require 2No cranes working in close proximity to each other and in a relatively small footprint.
Keltbray Lifting Services, working in collaboration with Keltbray Decommissioning, reviewed the various available cranes capable of carrying out a lift at this height, weight and radius and the decision was taken to use a TC2800 lattice jib crane for the main lift, along with a 450T mobile crane to provide access for the rigging team.
Using a 3D model of the structure and surround hard standing, a detailed lift plan was prepared which showed the planned location of each crane, the rigging arrangement, and the interface between both cranes during the lifting operations.
Following set up of the cranes on site, the next challenge would be in the attachment of a complex and heavy rigging arrangement at circa 70m in the air. Keltbray Lifting Services rigging team, assisted by Keltbray Decommissioning operatives working from inside the top tower, carried this task out safely in a careful and controlled manner.
Following attachment of rigging, Keltbray Lifting Services safely managed lifting operations, with Keltbray Decommissioning operatives removing remaining holding down bolts from yaw ring level to free up the nacelle load. The nacelle was landed on reconstructed pad to allow the remaining blades to be removed, prior to load out from site and transportation to a storage facility.
Technical Challenge 4 – Offloading Nacelle from Low Loader in Storage Facility
Following on from safe removal of the nacelle to grade level and load out, there was a requirement to offload in a storage facility to allow for forensic investigation works. This would prove challenging due to the weight (86T) and size of the nacelle structure.
A detailed design exercise was carried out which included a review of options for offloading. Due to limitations on head room and working space, it was decided that a Mega Lift system would be used, utilising the same lifting arrangement as the main lift and replicating the 4 points of the crane and lifting beam.
The access to the storage facility was tight and provided around 100mm clearance on either side of the load and around 200mm to the top.
Keltbray Lifting Services again managed the lifting operations and the nacelle was safely offloaded and handed over to the forensic team.
Technical Challenge 5 – Removal of Top Tower Section
The final challenge of the project was to remove the top tower section and safely store on site to allow for remedial works to be carried out prior to reinstallation. WHP carried out a detailed engineering review of the lifting arrangement, bolt removal and issued and designed check certificate for both, they also designed the top tower support pedestals and carried out insitu NDT testing once the top tower was safely at grade level.
Keltbray Lifting Services and Keltbray Decommissioning safely executed the tandem lift using two number cranes, and placed the top tower onto support pedestals.
Additional Information
This is the third wind turbine Keltbray has decommissioned, each one with a different approach. The first we rotated to grade level using pulling rope, the second one felled using explosives, and with this project we dismantled using large cranes, Keltbray offers a complete bespoke approach to each individual challenge we face, with a view to delivering the safest and most cost effective solution for our clients.