PAUT
Ultrasonic phased array testing is a powerful NDT technology and one whose use is growing rapidly, however it can seem complex to a person who has not worked with it. This self-guided tutorial is a basic introduction to ultrasonic phased array testing, both for newcomers and for more experienced users who want a review of basic principles. It begins with what phased array testing is and how it works, then outlines some considerations for selecting probes and instruments, and ends with links to phased array application notes and a phased array glossary. In addition to text and illustrations it includes a series of interactive Flash files as learning tools.
PAUT is an advanced method of ultrasonic testing that has applications in medical imaging and industrial testing. When applied to metals the PAUT image shows a slice view that may reveal defects hidden inside a structure or weld. Phased array uses an array of elements, all individually wired, pulsed and time shifted. A typical user friendly computerized setup calculates the time delays from operator input, or uses a predefined file: test angle, focal distance, scan pattern and so forth. The technique also provides a combination of various scans in the same equipment set-up. B-Scan is a side view, CScan is a top view and the S-Scan is a cross-sectional view. These views can be better understood in the Figure. From a practical viewpoint, ultrasonic phased arrays are merely a technique for generating and receiving ultrasound; once the ultrasound is in the material, it is independent of the generating technique. Consequently, many of the details of ultrasonic testing remain unchanged; for example; if 5 MHz is the optimum testing frequency with conventional ultrasonic, then phased arrays would typically Use the same frequency, aperture size, focal length and incident angle. As such, phased arrays offer significant technical advantages over conventional single-probe ultrasonic; the phased array beams can be steered, scanned, swept and focused electronically.
- Electronic scanning permits very rapid coverage of the components, typically an Order of magnitude faster than a single probe mechanical system.
- Beam forming permits the selected beam angles to be optimized ultrasonically by Orienting them perpendicular to the predicted defects, for example Lack of Fusion in welds.
- Beam steering (usually called sectorial scanning) can be used for mapping Components at appropriate angles to optimize Probability of Detection. Sectorial Scanning is also useful for inspections where only a minimal scanning length is possible.
- Electronic focusing permits optimizing the beam shape and size at the expected Defect location, as well as optimizing Probability of Detection. Focusing improves Signal-to-noise ratio significantly, which also permits operating at lower pulser voltages.
Overall, the use of phased arrays permits optimizing defect detection while minimizing inspection time. Phased arrays offer significant advantages over traditional radiography of welds as well:
- No safety hazards
- Inspection as soon as weld is cool
- Better defect detection and sizing
