Denmark’s CNC Onsite to offer onsite wind turbine blade root repairs

By WPED Staff | September 6, 2022

Blade root damage to older wind turbines previously could only be repaired at the manufacturing site, requiring expensive logistics and long downtime, which often left operators with no choice but to purchase a new blade or scrap the entire turbine. With its new portable tool developed to efficiently replace damaged inserts in blade roots, Danish company CNC Onsite will be the first to offer economical precision repairs carried out at the wind farm, eliminating transport costs — financial and environmental — as well as waiting times for a repair slot.

Embedded into the blade root during the manufacturing process, the threaded inserts that are critical for joining the blade to the nacelle hub can become loose over time. In older blades, microcracks can form, which allow contaminants such as grease and hydraulic oil to weaken the bonding. This ultimately endangers the structural safety of the blade root, especially when fatigue loading is high. At worst, this can result in the blade breaking away.

Blade root repaired at the wind park

With CNC Onsite's method, the rotor blade is dismounted using a crane before it is placed in a repair environment at the wind farm. The portable, automatic machining tool aligned to the blade drills away the faulty inserts from the composite material. Ensuring the cavity matches the exact diameter and shape of the replacement part, an additional, precise drilling process is performed so that the new part can be inserted and then fastened using bonding material.

"Repairing the blade root inserts onsite can be a complex operation. You need to be able to control several process parameters to ensure you do not do more damage to the blade and it is important to drill exactly in the center of the existing inserts," explains Søren Kellenberger, sales director and partner, CNC Onsite.

Developed in response to the needs of operators looking for an onsite repair solution, the new tool benefited from the company's proven CNC-controlled machine technology, used to perform repairs to the yaw ring and tower flanges in line with fine millimeter tolerances.

"Currently, the only way to repair wind turbine threaded inserts is to take off the whole blade and transport it to the manufacturer. The first challenge is the enormous costs of transporting the blade on public roads. Secondly it is difficult to get a repair slot as manufacturers are extremely busy building new blades.

"For every handling and transport process you risk damaging the blade structure, so in all aspects a repair job onsite is preferable when you can achieve the quality we are able to, with our new solution," adds Kellenberger.

CNC Onsite and We4Ce offer full-service solution

CNC Onsite has teamed with We4Ce, an international blade rotor and blade root connection expert, to deliver a complete repair solution focused on high-strength blade roots.

"The difficult parts of replacing a threaded insert are first of all the centering the replacement part and secondly the processing technology for the bond. Based on our track record since 2008, we have developed inserts with a design that considers both. This full solution offers consistent and stronger bond between the insert and the blade," explains Edo Kuipers, Engineering Manager and Co-owner of We4ce.

Older blade designs have shorter lifetime

The energy transition to using more green power means the blade manufacturers are not only running at full capacity producing new blades, but older blade models are often phased out after some five to 10 years, which means the mold has to be recreated. One of the most fragile components of the wind turbine, the blades are also the most expensive components accounting for some 25 to 30% of the build cost.

Replacing blades on older turbines is often not financially feasible. The operator may decide to keep the turbine running at reduced capacity or even decommission it. Keeping the turbines running is important to meet renewable energy targets and this repair service can play an important part in extending the lifetime of existing turbines.

The full repair solution available from autumn 2022

To haul a blade, an oversized load, not only costs many tens of thousands of Euros but also requires detailed planning and approvals, not to mention the downtime costs. The energy-efficient repair service from CNC Onsite will be offered at a fraction of these costs.

Efficient repair of wind turbines is increasingly a vital element of the renewable energy transition. Issues with threaded inserts are usually detected during maintenance and mostly occur in turbines older than 10 years. The new CNC Onsite blade root repair is estimated to take two to three days, depending on the number of faulty inserts, as opposed to previously spending many months at the manufacturer.

"From our many discussions with potential customers, it is clear there is a need for onsite repair. From late autumn this year we will be offering the service, which we believe is the first on-site method. This will be available for all blade sizes," concludes Kellenberger.

CNC Onsite's blade repair solution, as well as its flange milling tool for 10-meter turbines and a patented yaw ring repair method, will premiere at the WindEnergy Hamburg exhibition, 27-30 September, stand Hall B, stand EG.504.

News item from CNC Onsite