We assess the structural integrity of the components of a wind turbine nacelle after a fire

Fire protection in wind turbines is complex. Achieving total reliability of the protection system in these devices is complicated. Fires can mainly originate in the nacelle where the most relevant electrical, mechanical and structural components of the wind turbine are located; positioning systems, the slow speed shaft, the gearbox, the turbine, the control panels, racks, supports, etc.

The possibility of fire is particularly worrying for the wind farm operator due to the damage caused to capital goods, the production loss, and the harm to its image.

In order to restore the activity of the equipment it is necessary to change all the damaged elements or reuse them, evaluating their structural integrity beforehand.

Our materials engineering group assessed the damage to several components of a nacelle that had suffered a fire, analysing whether they showed a degradation in their mechanical properties for possible reuse.

The engineers relied on the criteria included in Chapter 11-Assessment of Fire Damage of standard API 579-1/ ASME Fitness-For-Service. Service suitability assessments are engineering appraisals conducted to demonstrate the structural integrity of equipment in service that may be damaged, or that may operate under specific conditions that could cause failure. It is tested for suitability to ensure that it operates properly and without the risk of breakdown.

This fire damage assessment standard sets out three steps to follow:

• Identification of heat exposed zones (HEZ).
• Risk analysis depending on the combination between the heat exposed zones and the different construction materials affected.
• Evaluation of the components (in case of risk), based on the following inspection techniques: metallographic analysis in the field, measurement of hardness and/or magnetic particles.

After evaluating the components, which presented a risk of failure, it was concluded that all of them could be reused; even four components whose galvanising coating had been partially damaged. Their repair was recommended to ensure corrosion resistance.

During the evaluation of the frame, multiple small cracks were detected, although not due to fire but rather induced during the manufacturing process, and we recommended their removal by surface grinding before reuse.