Wind Turbine Blade Defect Detection: Topic Overview

TL;DR Blade defect detection is the practice of finding the flaw classes a composite blade hides and judging each against the limit in IEC 61400-5 Table G.1, so the accept or repair decision rests on a measured number rather than on a surface impression.

Delamination limit

6 mm in any direction

Porosity cluster limit

3 mm diameter, under 3 % area

Wrinkle limit

3 degrees from nominal

Reference sensitivity

6 mm squared flat-bottom hole at 20 mm depth

Detection

99.2 % validated by ASNT Level III review

Bond line on a 100 m blade

over 1,200 linear metres

A blade hides its flaws because the material is thick and the surface stays smooth. A spar cap up to 80 mm of unidirectional laminate can carry a planar separation that a tap test rings true on. Porosity sits scattered through the thickness with no plane to point at. A kissing bond is an absence of signal, not a reflection, so a low-gain pass certifies it as sound.

That is why the limits are the useful part of the topic. Table G.1 caps delamination at 6 mm, a porosity cluster at 3 mm diameter, and a wrinkle at 3 degrees from nominal, while dry laminate and a foreign inclusion are not permitted at all. A 6 mm squared flat-bottom hole at 20 mm depth is the reference that proves a system reaches 99.2 % probability of detection, so the figure traces to a real artefact rather than a claim.

The practical consequence is that one pass carries several channels. A 64-element array steering through 40-70° images the planar defects, TOFD reads the volumetric ones, and the amplitude channel carries the dry-laminate signature. On a 256-channel system those arrive together, which is what lets a single scan apply four different limits on a blade that carries over 1,200 linear metres of bond line. A 256-channel system carries those four limits in one pass, where reading them by hand would take longer than a shift across four separate methods, so the machine replaces a routine rather than a person.

Every figure on this page traces to our own product and field documentation, so a claim here can be checked against the datasheet it came from.

Options at a glance

Defect class	Limit	Method that reads it
Delamination	6 mm any direction	PAUT sector scan
Porosity cluster	3 mm, under 3 % area	TOFD volumetric channel
Dry laminate	not permitted	PAUT amplitude drop
Wrinkle	3 degrees from nominal	PAUT ply-boundary reading
Foreign inclusion	not permitted	PAUT and TOFD together

How to work through this topic

01 Fix the acceptance threshold. Start from the threshold the zone carries, not from the method you happen to own. IEC 61400-5 Section 11 asks for volumetric detection of indications 6 mm and larger in the laminate plane, and DNV-ST-0126 tightens the leading edge to 3 mm, so the threshold is set before the probe is chosen.
02 Read the geometry off the drawing. Measure the thickness and the curvature the probe has to travel. A spar cap up to 80 mm of unidirectional laminate and a root transition of changing radius are two different scan problems, and the radius decides how the array is coupled.
03 Choose the modality pair. Pick modules by defect geometry, not by habit. PAUT images planar separations that lie parallel to the plies, TOFD catches volumetric clusters whatever their orientation, and running both on a 256-channel system puts the two mechanisms in one pass.
04 Automate the scan path. Put the probe on an encoder-driven carriage and let the path, not the technician, set coverage. A 600 mm spar cap falls to one longitudinal pass at 500 mm/s on a linear array, where a single-element probe needs 20 parallel passes and runs about five times longer.
05 Lock the evidence chain. Write the coverage map, the daily calibration and the indication log to the blade serial while the scan is running. It is the difference between a 3-day type-certification audit and a 3-hour document review, and it is what ISO 9712 qualification is there to sign.

Detailed pages in this topic

Frequently Asked Questions

What defects does a blade scan look for?

The classes IEC 61400-5 Table G.1 governs, delamination, porosity, dry laminate, wrinkle and foreign inclusion, plus the in-service modes such as leading edge erosion, lightning damage and crack growth. Each carries its own kind of limit rather than a single number.

Why can a surface method not find these defects?

Because most of them are internal. A planar separation inside 80 mm of laminate barely changes the surface, porosity sits scattered through the thickness and a kissing bond reflects almost nothing, so a visual or tap pass cannot reach any of them.

What is the reference that proves detection?

A 6 mm squared flat-bottom hole at 20 mm depth in a glass-fibre reference panel built to ASTM E2580. Reaching 99.2 % probability of detection on that artefact is what validates the system against a known defect rather than a claim.

How many limits does one scan apply?

Four or more. Delamination, porosity, wrinkle and the absolute exclusions each carry a different limit, and one pass on a 256-channel system collects the planar, volumetric and amplitude channels that apply them together.