While PAUT is becoming a popular approach for nondestructive inspections, it is important that users understand this technology, its limitations and how it should be applied.
Phased array (PA), commonly referred to as ultrasound in the medical field, has been extended for industrial applications and is quickly replacing conventional angle beam ultrasonic testing (UT). While conventional ultrasonic testing utilizes single crystal probes with a fixed beam angle such as 0⁰, 45⁰, 60⁰ and 70⁰, phased array by applying time delays on multiple crystals sweeps the beam over a range of angles. This feature allows full coverage and inspection with a single phased array probe instead of multiple fixed angle probes. The time delays applied to the individual crystals are mathematically calculated to focus and sweep the beam. These are called focal laws. Using a single PA probe instead of multiple conventional probes allows simplification of manual as well as mechanical and automated UT scanners. Another advantage of phased array ultrasonic testing over conventional ultrasound is that while conventional UT displays a time based A-scan signal, phased array UT displays a sectorial image representing cross-section of the tested part. The sectorial image is much easier to understand and interpret instead of an A-scan signal that requires plotting on a component drawing. Figure 1 shows phased array probe placed on steel block with three side drilled holes and a notch. The corresponding image shows a 1:1 relationship showing the three holes making it easier for the technician to understand and interpret. Similar displays can be seen when inspecting welds and other complex geometries.