Onshore Wind Turbine Blade Leading-Edge Erosion: Inspection and Repair Timing
Onshore wind turbine blade leading-edge erosion (LEE) starts when rain, hail or airborne particles strike the rotating nose of a composite blade. It can roughen or remove the topcoat or leading-edge protection (LEP), expose underlying layers and eventually create a cavity or structural concern. The practical answer is not simply to repair at a fixed turbine age: inspect the affected span and material, classify the condition, check for progression, and relate the finding to the turbine model, site performance and the owner's engineering basis. A broader onshore wind farm maintenance programme may contain this work, but the inspection question here is narrowly leading-edge erosion on land-based turbines.
How onshore leading-edge erosion develops
The IEA Wind Task 46 work on erosion drivers describes the first-order mechanism through the closing velocity, number of impacts and nature of the hydrometeors. A rotating blade sees much greater relative speed toward the tip than near the root, so damage commonly concentrates toward the outer span. Rain is the frequent driver; hail can be more severe per impact. Dust, sand, ultraviolet exposure and repeated temperature or humidity changes can then accelerate damage after the protective surface has been opened.
| Driver | Effect on erosion exposure |
|---|---|
| Operating speed and radius | Determine relative impact speed at each blade station, with the outer span generally experiencing higher speeds. |
| Weather | Rain intensity, droplet-size distribution, hail and the number of erosive events affect accumulation. |
| Surface system | Coating, LEP geometry, adhesion, manufacturing defects and previous repairs change the response. |
| Onshore site exposure | Local rain, convective hail, dust, cold cycles and operating strategy create site-specific histories. |
LEE should not be used as a label for every blade defect. Cracks, delamination, lightning damage, bond defects and trailing-edge splits may coexist with erosion but require different questions and evidence. The broader rotor-blade damage prevention guidance covers the wider damage-prevention context; this article stays with the erosion mechanism and the decision to inspect or repair it.
Classify the condition before deciding urgency
The IEA Wind Task 46 erosion classification system, developed with Sandia National Laboratories and industry partners, separates four dimensions: visual condition, mass loss, aerodynamic performance and structural integrity. These dimensions are related but not interchangeable. A small area of peeling LEP can disturb flow more than its area suggests, while a visual photograph cannot establish mass loss or hidden laminate damage. The system is intended to evolve, so the report, inspection procedure and acceptance basis should identify the version and criteria used.
| Level | Visual condition |
|---|---|
| 1 | Barely visible erosion or small pinholes without meaningful exposure of underlying structure. |
| 2 | Localised pitting or local LEP damage while protection remains broadly present. |
| 3 | Widespread or coherent pitting, or LEP compromised over a substantial area. |
| 4 | Topcoat and the layer immediately beneath it exposed over a notable area, with possible laminate involvement. |
| 5 | Notable substrate or laminate damage, or a leading edge open or eroding through structural layers. |
These visual levels are a screening language, not a universal repair authorisation. Record whether LEP is present, the maximum and typical severity, the spanwise distribution, and the exact area, width, depth or exposed layer. A report that says only "blade erosion: moderate" cannot support a defensible repair window or a repeat comparison.
Inspection workflow for an onshore turbine blade
An effective inspection is a traceable comparison, not just a set of close-up photographs. Define the decision first: routine baseline, post-hail or severe-weather check, suspected performance change, repair verification or progression review. Then use the least intrusive method that can answer that question and escalate when the evidence is insufficient.
- Set the baseline: collect the turbine model, blade drawing, LEP or coating type, operating hours, previous defect maps, repair records and relevant weather events.
- Plan coverage and access: ground cameras or a drone can screen the three blades, while close visual inspection or rope access may be needed for scale, surface feel, depth, adhesion or repair preparation.
- Use a fixed location system: identify blade, pressure or suction side, distance from root, chordwise position and inspection direction, then photograph with consistent lighting and a scale.
- Verify suspect areas: distinguish loose or peeling LEP from erosion of the blade surface, and examine exposed filler, laminate, cracks, delamination, moisture or an open cavity with the appropriate close method.
- Correlate performance: compare power and wind-speed data with availability, curtailment, yaw, icing, soiling, turbulence and other losses before attributing an output change to erosion.
- Close the evidence loop: report coverage, inaccessible areas, measurements, visual and other classifications, uncertainty, recommended action, priority and the date or trigger for follow-up.
A drone or ground-camera survey is valuable for consistent coverage, but it can miss small damage, unfavourable viewing angles, underside details, surface texture and defects hidden by dirt or glare. A close indication that could affect repair or structural integrity should be escalated rather than downgraded because it is difficult to photograph. The general blade-inspection overview explains the wider inspection rationale; the LEE-specific scope still needs its own location and classification records.
How Leading-Edge Erosion Can Affect Annual Energy Production
Leading-edge roughness changes boundary-layer transition and the lift-to-drag behaviour of the affected airfoil. The resulting AEP effect depends on the airfoil sections, radial damage distribution, rotor and controller, wind climate, wakes and the condition of the rest of the turbine. Model results are therefore useful for screening and cost comparison, but a percentage from another turbine is not a measurement of an onshore asset.
| Evidence | Reported result | How to use it |
|---|---|---|
| Sandia utility-scale study | Up to 5% AEP reduction for a heavily eroded blade in the studied case. | The work included a modelled tip-region NACA 633-418 airfoil, so the value is a scenario, not a generic onshore allowance. See Sandia's research summary. |
| 2018 NREL reference-turbine study | Calculated 2% to 3.7% AEP reductions for specified contamination and erosion conditions. | The peer-reviewed analysis used a 5-MW reference turbine and tip-airfoil model; it was not a universal field result. |
| IEA Wind Task 46 report | One set of eroded cases spans roughly 1.16% to 2.10% AEP loss. | The 2025 AEP report modelled 15-MW and 22-MW reference turbines and found different responses by controller and modelling approach. |
| Site SCADA and weather data | Can show whether a power-curve change is plausible at the inspected asset. | Attribution remains uncertain when wind conditions, availability, curtailment, soiling or controller behaviour also change. |
For an onshore repair decision, compare the inspected damage map with the actual turbine model and its power data, not with a headline loss percentage. The business case should include lost production during access and curing, repair cost, expected damage progression, the chance of a missed defect and the value of restoring the aerodynamic surface. A field result that cannot separate those effects should remain qualified rather than presented as proof of an erosion-only loss.
Leading-Edge Erosion Repair Timing and Escalation Criteria
The following ladder is a practical way to organise evidence; it is not a replacement for the blade manufacturer's instructions, the owner's acceptance criteria or an authorised engineering decision. The urgency rises when damage reaches the laminate, grows between inspections, affects the outer high-speed span, creates loose material or is accompanied by a credible structural indication.
| Response | Typical evidence | Next action |
|---|---|---|
| Monitor and trend | Discolouration, isolated pinholes or minor pitting with intact protection. | Establish a measured baseline and revisit it at the approved interval or after a relevant weather event. |
| Plan a campaign repair | Local or widespread LEP failure, peeling or roughness without confirmed laminate exposure. | Set a repair window using damage growth, weather, access, production and material-cure constraints. |
| Short-interval engineering review | Exposed underlying layers, suspected delamination, crack-like indications, water ingress, rapid progression or uncertain depth. | Obtain close evidence and an engineering or repair assessment before relying on the next routine visit. |
| Immediate escalation | An open leading edge, through-laminate damage, loose material or a credible safety-significant structural condition. | Follow the site's isolation, operating-restriction and engineering-escalation procedure. An article or photograph cannot authorise continued operation. |
Control the repair scope and the follow-up
Do not select a filler, tape, coating or composite repair from a photograph alone. The work pack should identify the damage boundaries, surface preparation, compatible material system, environmental and curing limits, profile or roughness target, quality checks, documentation and any engineering approval. Surface-only repair and laminate repair are different scopes; the latter may need a designed composite repair and a separate integrity decision.
Repair technology is still developing. A 2026 peer-reviewed Oak Ridge National Laboratory study compared a vitrimer coating with a thermoplastic resin using blade materials and laboratory tests. Its adhesion and healing results are relevant research, not a blanket field acceptance criterion for every onshore blade, climate or OEM system.
- Photograph and measure the repaired span using the same coordinate system as the original finding.
- Record preparation, materials, batch information, environmental readings, cure evidence and deviations from the approved procedure.
- Check the repaired profile, edges, adhesion and adjacent damage before returning the blade to the agreed operating state.
- Set a follow-up trigger based on the repair system, site exposure, observed growth and the decision the next inspection must support.
After the repair, keep the image map, material records, inspection limitations and any power-data comparison in the turbine history. The regular maintenance planning guide provides the broader condition-based maintenance context; for LEE, the useful follow-up is a repeatable record of damage growth, repair performance and site-specific production evidence.
Prepare the onshore erosion evidence pack
- Turbine model, serial number, blade configuration, operating hours and LEP or coating specification.
- Previous inspection images and maps with the same blade and span reference, plus repair and warranty history.
- SCADA, power-curve and meteorological data with availability, curtailment, icing, soiling and unusual-event notes.
- The required coverage, access method, shutdown or rotor-position controls, weather limits and rescue arrangements.
- The classification basis, measurements, acceptance criteria, repair procedure and escalation route before mobilisation.
Limits of an erosion inspection
An onshore LEE inspection documents condition within a defined method, date and coverage. It does not prove that hidden damage is absent, establish remaining life, certify fitness for service or determine a repair design without the required engineering basis. A modelled AEP percentage is not a guarantee of lost revenue, and a stable power curve does not rule out local structural deterioration. The Sandia uncertainty study identifies initiation time, growth rate, blade design, operating conditions and atmospheric conditions as variables that can change the result. State those limitations plainly so the next decision is proportionate to the evidence.