IEC 61400-5 Section 11: Blade Manufacturing NDT Requirements

What the standard covers

The clause covers the primary structure rather than the whole blade. The spar cap to shell bond, the shear web to shell bond and the spar cap laminates sit inside it, inspected volumetrically and recorded per blade. Anything with a bond line carrying primary load falls in scope, and the coverage is total, not sampled.

What it demands

• Volumetric inspection of the primary bond lines and spar cap laminates, at 100 % rather than by sample
• A method capable of detecting indications 6 mm and larger in the plane of the laminate
• Inspection before the blade leaves the factory, so the evidence exists at the gate
• A record per blade that an auditor can trace, not a campaign summary

How it lands on a blade scan

The clause rules methods in and out by that 6 mm floor. Visual inspection and tap testing are surface methods and cannot meet it, so the choice narrows to ultrasonic or radiographic. Radiography is impractical on blades thicker than 60 mm of glass fibre, which is most of a modern cap, so PAUT plus TOFD is the practical combination. A gantry scans at 500 mm/s and covers a 600 mm cap in one longitudinal pass, where a single-element probe needs 20 passes, so the clause is met at production speed rather than in spite of it.

How to apply it to a blade

Run these checks in order. By Step 5 the scan plan has the threshold, the geometry and the record it needs.

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.

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