Erosion Depth Measurement on Blade Leading Edges

Author: RAS Thermal Co., Ltd. · Updated 2026-10-07

TL;DR Measurement: remaining wall thickness at plus or minus 0.1 mm with a 5 MHz dual-element transducer. Loss rates: coating 0.5-1.0 mm per storm season, bare glass 2-5 mm per year. Consequence: AEP loss 2-5 % per affected blade. Money: EUR 30,000-75,000 a year on a 5 MW offshore machine earning about EUR 1.5M.

A drone image confirms erosion along the leading edge, and the question is how much laminate is actually left. Erosion removes material, so the measurement that matters is remaining thickness, not the presence of a scar. Raindrops land at 80-90 m/s and strip 0.5-1.0 mm of coating in a single storm season. Once the coating is gone, the bare glass erodes at 2-5 mm a year. A drone image cannot tell 0.5 mm from 3 mm of loss, and that gap is exactly the one between a cosmetic touch-up and a structural grind and fill.

Common root causes

Root cause	What you see	Where it bites
Coating loss from rain and hail	a smooth recession along the leading edge with the coating gone	tip and outboard leading edge at speed
Bare glass erosion after coating loss	a rough scar deepening into the laminate season on season	the leading edge once coating is stripped
Impact damage at the tip	localised pits and gouges where speed is highest	outboard leading edge and tip
Recurring erosion after a cosmetic fix	the same zone back within a season because depth was never measured	repairs made from images alone

What the numbers allow

A 5 MHz dual-element transducer on a crawler maps remaining wall thickness to plus or minus 0.1 mm and overlays it on the blade model. That is the number the repair decision needs. The economics back it up, because AEP loss from erosion roughness runs 2-5 % per affected blade, and on a 5 MW offshore machine generating around EUR 1.5M a year that is EUR 30,000-75,000 gone annually. A ground-and-fill on the wrong blade costs far more than the scan that would have sized it.

Measurement: remaining wall thickness at plus or minus 0.1 mm with a 5 MHz dual-element transducer
Loss rates: coating 0.5-1.0 mm per storm season, bare glass 2-5 mm per year
Consequence: AEP loss 2-5 % per affected blade
Money: EUR 30,000-75,000 a year on a 5 MW offshore machine earning about EUR 1.5M

How to confirm it

Work down this list in order. The first check that changes the result has found the cause.

Screen with the drone first. Use the drone pass to locate the eroded zones cheaply, then treat its images as a map of where to scan rather than as the measurement itself.
Deploy the gauge to the marked zones. Run the crawler along the marked leading edge and let the dual-element transducer map thickness across each zone rather than at a single point.
Set the threshold before scanning. Agree the remaining-thickness threshold for a structural repair in advance, so the scan result maps straight onto a disposition.
Overlay the result on the model. Map the thickness C-scan onto the blade geometry so every point below threshold is located, and by how much, rather than left as a rough region.
Decide from the number. Split the zones into cosmetic and structural from the measured thickness, because that single split is what the drone image could not make.

Prevention

Re-profile or re-coat on measured thickness rather than on a photographic impression, and inspect on a schedule matched to the site erosion rate. One North Sea contractor found 30 % of blades slated for structural repair from drone images alone still had enough laminate when the thickness was measured, and across a 50-turbine farm the unnecessary structural jobs ran to about EUR 180,000. Measure before you grind.

The numbers below are drawn from the equipment records and field campaigns this site already publishes, not from a generic catalogue.

Frequently Asked Questions

Can a drone measure leading edge erosion depth?

No. A drone image shows that erosion exists and where, but it cannot separate 0.5 mm from 3 mm of loss. On a 5 MHz dual-element gauge the remaining thickness is mapped to plus or minus 0.1 mm, and that is the number a structural decision needs.

How fast does leading edge erosion progress?

Raindrops arrive at 80-90 m/s, which strips 0.5-1.0 mm of coating across a storm season. Once the coating is gone the bare glass erodes at 2-5 mm a year, so the loss is a rate, and the scan measures where on that rate a blade sits.

What does erosion cost in lost production?

AEP loss from leading-edge roughness runs 2-5 % per affected blade. On a 5 MW offshore turbine earning about EUR 1.5M a year that is EUR 30,000-75,000 gone annually, per machine.

Why not repair every erosion scar structurally?

Because most do not need it. One North Sea contractor found 30 % of blades slated for structural repair from images alone still had enough laminate, and the unnecessary jobs across a 50-turbine farm ran to about EUR 180,000. The thickness number avoids that.

Bottom line: Erosion calls for a thickness number, not a photograph, because the whole repair decision sits between 0.5 mm and 3 mm of loss. Screen with the drone, measure the marked zones to plus or minus 0.1 mm, and split cosmetic from structural on the number that comes back.