Phased array ultrasonic testing (PAUT)

A conventional ultrasonic probe holds one piezoelectric element, fixed at one angle, producing one A-scan — a single trace of echo amplitude against depth — at one probe position. Covering a full weld cross-section means physically moving or swapping the probe through every angle and position the joint requires, one trace at a time, with the operator holding the geometry in their head between readings.

A PAUT probe replaces that single element with an array, typically 16 to 128 elements, each driven by its own pulser under a programmable time delay. Changing the delay law steers the beam angle electronically across a range and can sweep through that whole range in milliseconds rather than by moving the probe. The output of one sweep is a sector scan — an S-scan — that plots every angle in the swept range against depth as a single cross-sectional image, from one probe position. What used to be a series of separate A-scans, each requiring the operator to reposition the probe and reason about how they fit together, becomes one image the operator reads directly.

This is a resolution gain as well as a speed gain. Because focal depth is programmable rather than fixed by geometry, a PAUT focal law places a tight beam at a chosen depth, and a scan plan can stack laws to keep resolution where a conventional single-element beam has already spread past its near field, which is part of why PAUT is the default volumetric route for planar, tightly closed imperfections such as lack of fusion that radiography routinely misses. The sector scan does not replace the acceptance decision — that still comes from the governing standard’s quality level applied to what the scan finds — but it is the record an inspector and an auditor examine to see how that finding was reached, in a way a single conventional A-scan trace cannot show on its own.