PAUT vs Radiography for Wind Blade Laminates

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

TL;DR Standard position: Radiography satisfies the volumetric requirement, Ultrasonic PAUT satisfies the volumetric requirement. Blade thickness limit: Radiography impractical beyond 60 mm of glass fibre, Ultrasonic PAUT works through 80 mm of unidirectional laminate. Production effect: Radiography safety exclusion zone stops the line, Ultrasonic PAUT runs inline at 500 mm/s. Output: Radiography a projected image of the volume, Ultrasonic PAUT a C-scan map of amplitude and depth.

IEC 61400-5 names ultrasonic testing and radiography as the methods that satisfy its volumetric requirement, so radiography is permitted rather than excluded. On a blade line it is rarely used, and the reason is a thickness rather than a rule.

The dimensions that decide

Dimension	Radiography	Ultrasonic PAUT
Standard position	satisfies the volumetric requirement	satisfies the volumetric requirement
Blade thickness limit	impractical beyond 60 mm of glass fibre	works through 80 mm of unidirectional laminate
Production effect	safety exclusion zone stops the line	runs inline at 500 mm/s
Output	a projected image of the volume	a C-scan map of amplitude and depth

Which way the call goes

The deciding number is 60 mm. Radiography is impractical on blades thicker than 60 mm of glass fibre, and a modern spar cap can reach 80 mm of unidirectional laminate, so the method drops out exactly where the load is highest. The safety exclusion zone is the second reason, because a radiography bay on a production line stops the line for the duration of the exposure. PAUT scans the same 80 mm at 500 mm/s inline and returns a C-scan map rather than a film, which is why a blade line reaches for the ultrasonic route even though the standard permits both.

How to choose between them

Run these checks in order. By Step 5 the choice follows from the geometry and the threshold rather than from habit.

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.
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.
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.
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.
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.

Values quoted here come from the same verified data the product pages carry, so this page and its sources agree line for line.

Frequently Asked Questions

Does IEC 61400-5 allow radiography on blades?

Yes, it names radiography as a method that satisfies the volumetric requirement. The practical limit is thickness, because radiography is impractical beyond 60 mm of glass fibre and a modern spar cap can exceed that.

Why is radiography impractical on thick laminates?

Because the required penetration rises with the glass-fibre thickness, and beyond 60 mm the method stops being practical for a production environment. A spar cap up to 80 mm of unidirectional laminate sits past that line.

What else rules radiography out on a line?

The safety exclusion zone. A radiography bay stops production flow for the exposure, which is hard to fit around takt time on a blade line that produces a shell per mould per day.

What does PAUT return instead?

A C-scan map of amplitude and depth rather than a projected film, and it runs inline at 500 mm/s through the 80 mm cap. That is why the ultrasonic route is the one a blade line actually uses.

Bottom line: The standard permits radiography, the thickness decides against it, and 60 mm of glass fibre is where that turns. Scan the 80 mm cap with PAUT inline at 500 mm/s, and keep radiography for the thin sections where it still fits.