TL;DR Phased array ultrasonic testing is the method that satisfies IEC 61400-5 at production speed, because a 64-element array steers a 40-70° sector through the thickness and covers a 600 mm spar cap in one pass where a single-element probe would need 20.
Array
64 elements
Sector scan
40-70°
Channels
up to 256
Cap coverage
600 mm in one longitudinal pass
Single-element equivalent
20 parallel passes, about 5x longer
Bandwidth
0.5-10 MHz
The beam control is what changes the economics. A phased array steers and focuses electronically, so the mechanical raster scanning that makes single-element work slow disappears. A 600 mm spar cap falls to one longitudinal pass at 500 mm/s, and the 40-70° sector images separations inclined steeply to the surface that a fixed-angle probe would pass over. Multiply the pass count by five and the single-element route stops fitting a takt time.
The pairing is deliberate rather than incidental. PAUT images planar separations that lie parallel to the plies and it carries the amplitude signature of dry laminate, while TOFD reads volumetric clusters whatever their orientation. Table G.1 caps delamination at 6 mm and a porosity cluster at 3 mm, so a pass that reads only planes can miss a cluster near the tight limit, and a pass that reads only volumes can miss a flat separation. A 256-channel system runs both in one scan.
The number the method is measured against comes from a reference rather than a brochure. A 6 mm squared flat-bottom hole at 20 mm depth in a glass-fibre panel built to ASTM E2580 is the artefact behind the 99.2 % probability of detection, and a 0.5-10 MHz bandwidth on the array lets the same setup interrogate the panel and the blade. That is what makes the detection figure traceable and the amplitude channel comparable from one blade to the next.
Read the figures as sourced, not as marketing. Each one sits in the documentation we already publish on this site.
Options at a glance
| Method | Reads | Limit it serves |
|---|---|---|
| PAUT sector scan | planar separation parallel to plies | 6 mm delamination |
| TOFD | volumetric scatter, any orientation | 3 mm porosity cluster |
| PAUT amplitude | dry laminate and unbonded interfaces | not permitted |
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
Why is PAUT used on blade spar caps?
Because it steers a 40-70° sector through the thickness and covers a 600 mm cap in one longitudinal pass at 500 mm/s, where a single-element probe would need 20 parallel passes and about five times the time. That is what lets 100 % coverage fit a production cadence.
Why pair PAUT with TOFD?
Because they cover two defect classes with two different limits. PAUT images planar separations against the 6 mm delamination limit, and TOFD reads volumetric clusters against the tighter 3 mm porosity limit, so one pass answers both.
What proves the detection figure?
A 6 mm squared flat-bottom hole at 20 mm depth in a glass-fibre reference panel per ASTM E2580. Reaching 99.2 % probability of detection on that artefact is what ties the method to a known defect rather than a claim.
What sector does the array steer?
A 40-70° sector, which images separations inclined steeply to the surface that a fixed-angle probe would pass over. The sweep happens electronically in one pass rather than by moving the probe by hand.
Standards and sources
- IEC 61400-5:2020, Wind energy generation systems, Part 5: Wind turbine blades
- DNV-ST-0126, Support structures for wind turbines
- DNV-ST-0376, Rotor blades for wind turbines
- ISO 9712:2021, Non-destructive testing, qualification and certification of NDT personnel
- ASTM E2580, Standard practice for ultrasonic testing of flat panels of polymer matrix composites
- ASTM E426, Standard practice for electromagnetic examination of tubular products
- ASME BPVC Section V, Nondestructive Examination
- ASNT SNT-TC-1A, Personnel qualification and certification in nondestructive testing