Leading Edge Erosion Failures

What causes leading edge erosion?

Leading edge erosion is caused by impacts from foreign objects, including:

• Rain
• Ice/snow
• Hailstone
• Air dust/particles
• Insects

As wind turbine blades rotate at high speeds, those apparently negligible sources listed above become abrasive on the blades leading edge surface, wearing away the protective coatings/tape protection and exposing the composite laminate structure underneath that can jeopardise the structural integrity and reducing the WTG performance and power production.

When a rain droplet impacts the leading edge blade surface, energy is released and propagated to the surface, undermining the surface progressively. Initially, there is no mass loss but at some point, coat protection wears away resulting in a roughness surface weaker than initially against new particles impact.

Appearance

Leading edge erosion can occur from the start of a wind turbine’s operation. Early on, this erosion may not be visible through standard visual inspections. However, as rain droplets, dust particles in the air, insects, and other debris continuously strike the surface, small pits begin to form. These pits serve as nucleation sites, leading to further damage over time.

Once the cracks appears and the protective layer wears away, the laminate underneath is visible as a different colour due to the lack of paint. The surface also becomes rough and aerodynamic efficiency and performance are greatly impacted.

A rougher blade profile causes an early transition from laminar to turbulent airflow, resulting in reduced AEP, as the blade is no longer capturing as much energy from the wind as it should. The appearance of the damage varies based on the extent of the erosion.

Leading edge erosion progress from 1 year

Year 1

Year 2

How leading edge erosion progresses

Leading edge damage develops throughout the blade’s lifespan. In the early stages, only minor tear marks and insect impacts are visible, with minimal effect on the coating or tape. As damage progresses, surface pits become noticeable, and eventually, the paint detaches, exposing the laminate and creating an uneven, rough surface.

The evolution of this damage can be tracked using solutions such as regular visual or drone inspections. With expert analysis and severity ratings, informed decisions can be made about when to take action. Proactively monitoring and addressing leading edge erosion can significantly reduce maintenance costs and enhance blade performance.

How to detect blade leading edge erosion

Discussion

Leading edge erosion is a well-known issue suffered across both onshore & offshore turbines, although in offshore wind farms it becomes more significant due to the site conditions and the cost of repairs.

To solve the loss of energy performance, it is important to find the right solution to each specific site condition and blade.

OEM’s usually provide a 5-year warranty period covering leading edge issues, after that the wind farm operator becomes responsible for the issue.

The most common leading edge protection solutions are:

• Protective coating: These can be applied in mould or post mould during the manufacturing process
  In mould (gelcoat) is typically an epoxy, polyester or polyurethane, similar to matrix material.
  Post-mould: know as flexible coating usually made of polyurethane are usually applied after blade demoulding in a different manufacturing task.
• Leading edge tapes: These are similar to flexible coating, it is a tape added during the manufacturing process when the blade is de-moulded.
• Erosion shields: rigid or semi-flexible shields designed to provide long-lasting protection. While some are made of metal, potential challenges include poor adhesion to the blade surface, excessive stiffness that increases stress on the blade, and issues with lightning strikes in metal-based solutions.

Severity rating

Rank 1 Mild erosion on leading edge blade from mid-span to tip. Common wear, droplet marks, and insects on the surface.

Detection:

Visual

Recommended action:

No action required, just monitor the evolution.

Rank 2 Pits and coating tape protection wear away. Leading edge erosion penetrates down the blade laminate.

Detection:

Visual

Recommended action:

Repair within 6 months. Monitor progression. Normal operation until repair.

Rank 3 Erosion breaks the first laminate layer. Clear uneven zone, no painting on the surface.

Detection:

Visual

Recommended action:

Repair within 3 months. Monitor evolution. De-rated power could be needed in certain weather and operation conditions.

Rank 4 Damage has progressed, impacting the whole laminate thickness, creating a laminate discontinuity/hole jeopardising the blade structural integrity.

Detection:

Visual

Recommended action:

Repair immediately. WTG should be shut down.