Setting Up PAUT Like a Pro: Probe, Wedge & Angle Choices

Setting Up PAUT Like a Pro: Getting Probe, Wedge & Angle Selection Right

PAUT is a wonderfully capable technique, but its performance depends entirely on how well you prepare the inspection. A phased array system can produce exceptional images—or a wall of noise—based solely on the decisions made before scanning starts. In practice, the most reliable inspections come from technicians who begin with the weld geometry and material behaviour, then build their setup around those constraints. The catalog comes later.

Choosing the Right Probe: Frequency, Aperture, and Element Behaviour

Probe selection sets the tone for the entire inspection. Frequency is usually the first question, because it governs the balance between penetration and resolution.
For carbon steel welds, the 2–5 MHz range is a comfortable starting point. When the material becomes thick, highly attenuative, or both, inspectors often shift toward 2–3.5 MHz to maintain a workable signal-to-noise ratio. Conversely, when the priority is sharper flaw definition—particularly near sidewalls—higher frequencies around 5–7.5 MHz can deliver noticeably cleaner edge resolution.

Aperture then shapes the acoustic field. A larger effective aperture tightens the beam and improves focusing, but only if the part geometry allows the probe to sit correctly. Curved surfaces and limited access can quickly reduce the theoretical advantages. Element pitch also plays an often-overlooked role: a tighter pitch refines focusing performance but increases the risk of spatial aliasing when pushing steering angles to their limits. This is why good focal-law design still matters, even with modern PAUT instruments.

The Wedge: Where Theory Meets Real-World Coupling

If the probe defines the beam, the wedge dictates how that beam actually enters the material. Most weld geometries respond well to shear wave wedges between 45° and 70°, but angle alone doesn’t tell the full story.
The delay line controls how cleanly you can separate interface echoes from the target region. Too little delay compresses everything into one cluster of signals; too much weakens near-surface sensitivity. Stability matters just as much: the wedge needs to sit firmly over caps, spatter, and small irregularities without rocking, or the beam path becomes inconsistent.

On small-diameter pipe, wedge curvature becomes essential. A poorly matched radius produces lift-off variations that are immediately visible in signal quality. Mini-wedges are increasingly used to manage tight access zones while maintaining stable coupling. In these environments, a “good enough” wedge rarely is.

Angle Strategy: Building a Scan That Matches the Weld

Once probe and wedge are matched to the application, angle selection becomes the backbone of the inspection. A sectorial scan covering roughly 40° to 75° in small increments offers broad visibility without generating an unwieldy file.
More refined angle groups then bring precision:

• Lower angles in the 40–55° range target the root, including cap/root land and potential lack of penetration.

• Higher angles around 60–70° illuminate sidewalls and the fusion line, where lack of fusion and embedded cracks often hide.

When geometry complicates the inspection—offset bevels, access restrictions, or asymmetric caps—adding skew angles of ±10° to ±20° often reveals indications invisible in a single scan plane. In many field situations, skew data is the difference between “suspected” and “confirmed.”

Why Setup Still Matters More Than Software

Modern PAUT systems offer powerful correction features, but none of them compensate for a poorly chosen frequency, an unstable wedge, or steering angles that don’t match the weld profile.
When the acoustic field is configured deliberately, PAUT behaves exactly as experts expect: high-resolution imaging, repeatable sizing, and datasets that stand up under review. When it isn’t, even the most advanced instrument feels inconsistent.

If you need guidance selecting the right probe and wedge for your next inspection, our team is always available to support you.
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