The FP7-funded CORETO project is set to spearhead new structural rehabilitation techniques that will make repairing wind turbine blades possible on site. The CORETO consortium explains how the adapted method works and how it will benefit the industry.

Current state-of-the-art turbines are increasing in size, providing multimegawatt power output. In order to generate such power, turbine rotor blade diameters exceeding 100m and nacelle heights of 120m are becoming standard.

As the size of wind turbines increases, and their deployment becomes more widespread and remote, it is increasingly important that systems are put in place to monitor their condition in real time.

Such monitoring offers significant cost of ownership savings through condition-based maintenance, reduced downtime and diminished likelihood of catastrophic failure.

Although recent efforts towards condition-based maintenance have taken place, there has been limited action concerning the next step to occur following the localisation of potential blade damage. Existing solutions require, in most cases, the disassembly of the turbine blades and their shipment to specialised composite repair facilities, which results in increased time and costs.

Step-by-step turbine blade repair

Statistics show that the largest proportion of incidents by far occur as a result of turbine blade failure. It is clear that turbine blade failure is an ongoing, seriously hazardous occurrence. Furthermore, these numbers indicate a rising trend that is expected to continue as the number of turbines built increases and the existing turbine fleet ages.

As part of the new FP7-funded CORETO project, adapted tooling is being developed that complies with wind turbine specificities and requirements – the tools are easily mounted, lightweight, fast and robust. This will enable in-situ performance of the three major composite turbine blade repair steps: non-destructive inspection, surface preparation and hot bonding.

The project estimates that large-scale reductions could be achieved, in terms of system availability and cost, by minimising the disassembly of blades and their transportation to repair shops for rehabilitation.

A faster, simpler rehabilitation process

To achieve non-destructive inspection, existing ultrasonic equipment is being adapted to enable fast and reliable tracing of the blade damage’s nature and boundaries with minimum infrastructure requirements. Ultrasonic flaw detectors will be combined with specific probes to enable wider area coverage.

"The systems developed thanks to the CORETO project will enable 90% of wind turbine blades to be repaired on site."

To realise the surface preparation, a fully automated portable laser system is being developed to remove flaws and prepare the surface prior to repair. This system will be placed on the blade area to be processed and the required geometry of the damaged area will be created by entering the desired dimensions into a laptop control computer. The benefits of this new system will include higher geometrical accuracy, reduced processing time and, most importantly, fully automated control, reducing the need for skilled personnel and eliminating human error.

Finally, in order to perform the hot bonding and vacuum bagging, specially designed heating blankets and vacuum holders are being developed with the aim of making the simultaneous application of heating and vacuuming on site easier, and to simplify and accelerate the overall repair process.

Reduced costs and downtime

The improved systems developed thanks to the CORETO project will enable 90% of wind turbine blades to be repaired on site. This will bring about large reductions in the cost of repairs, as well as the resultant costs of downtime, blade disassembly and transportation of blades onshore for rehabilitation.

Globally, such systems will contribute significantly to the efficiency of wind power production. In addition, they will bring these newly adapted repair solutions to the increasing number of installations suffering such failures.