phased array ultrasonic testing PAUT

Phased array ultrasonic testing (PAUT) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are discover flaws in manufactured materials. Single-element, monolithic probes emit a beam in a fixed direction. To test a large volume of material, a conventional probe must sweep the beam through the target. A phased array probe can be focused and swept electronically without moving the probe. The beam is controllable because a phased array probe is made up of multiple small elements, each of which can be pulsed individually. The term phased refers to the timing, and the term array refers to the multiple elements.

What is Phased Array Ultrasonic Testing (PAUT) and how does it work?

The phased array probe consists of multiple ultrasonic transducers, pulsed individually. By varying the timing, a pattern of constructive interference results in radiating a quasi-plane ultrasonic beam at a set angle. By varying the progressive time delay the beam can be steered electronically. It can be swept through the object and the data from multiple beams are combined to create a visual image, effectively a slice through the object.

 

How does an ultrasonic scanner work?

The principles of a scanner used in medical ultrasonic imaging, consists of a beamforming oscillator. This produces an electronic signal consisting of pulses of sine waves, oscillating at an ultrasonic frequency, which is applied to an array of ultrasonic transducers in contact with the skin surface. The transducers convert the electric signal into ultrasonic waves traveling through the tissue. The timing of the pulses emitted by each transducer is controlled by programmable delay units, in turn controlled by a control system.

Wavefronts are spherical, but they combine to form plane waves, creating a beam of sound traveling in a specific direction. Since the pulse from each transducer is progressively delayed going up the line, each transducer emits its pulse after the one below it. This results in a beam of sound waves emitted at an angle to the array. By changing the pulse delays, the computer can scan the beam of ultrasound in a raster pattern across the tissue. Echoes reflected by different density tissue, received by the transducers, build up an image of the underlying structures.

 

Advantages and benefits of phased array ultrasonic testing

  • The primary method for ultrasonography
  • Multiple probe elements produce a focused beam
  • Focal spot size depends on probe active aperture (A), wavelength (λ) and focal length (F)

 

 

 

  • Produces an image that shows a definitive slice through the object
  • Compared to conventional ultrasonic testing systems, PA equipment is more complex and expensive
  • Technicians require more experience and training

 

 

Phased array speed and accuracy

Phased array results are obtained very quickly. Advanced software incorporates full matrix capture (FMC) and total focusing method (TFM) techniques for data acquisition from as many as 64 channels. Data processing builds detailed images that give the detailed information on the size, characteristics and flaws or defects. Phased array can also be combined with the time-of-flight diffraction (TOFD) to enhance the definition and accuracy.

Inspection results are instantaneous, confirming detailed identification of defects very quickly. PAUT instruments produce digital records to meet compliance requirements. Additional advantages of phased array inspections techniques include a very high probability of detection (POD) across fatigue and stress corrosion cracks. The ability to assess through-wall depth to locate defects and instant calculation of defect height measurements as an indicator of flaw severity. Additionally, the technique can discriminate among defects throughout the material thickness in a proximate location.

Inspections can also be automated with a crawler for circumferential or axial weld scanning. In summary, phased array gives standardised, accurate detection of flaws and is ideal for weld inspections, wall thickness measurements, and corrosion detection.

 

Phased array ultrasonic testing applications and use in industry

Phased array is widely used for nondestructive testing (NDT) in several industrial sectors, such as construction, oil and gas and power generation. This method is an advanced NDT method that is used to detect discontinuities i.e. cracks or flaws and thereby determine component quality. Due to the possibility to control parameters such as beam angle and focal distance, this method is very efficient regarding the defect detection and speed of testing. Apart from detecting flaws in components, phased array can also be used for wall thickness measurements in conjunction with corrosion testing.

 

 

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References

  1.  Corrosion under pipe support inspection. Retrieved on July 13, 2012.
  2. ^ Phased Array (PA). Retrieved on July 13, 2012
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  4. ^ ASTM, E2700 (2012). Nondestructive Testing, vol 3.03, Contact Ultrasonic Testing of Welds using Phased Arrays. Conshohocken, PA: American Society for Testing of Materials. pp. 1536–44. ISBN 978-0-8031-8729-0.
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  6. ^ ASTM, E2491 (2012). Nondestructive Testing vol 3.03, Evaluating Phased Array Characteristics of Phased Array Ultrasonic Testing Instruments and Systems. Conshohocken, PA: American Society for Testing of Materials. pp. 1358–75. ISBN 978-0-8031-8729-0.
  7. https://en.wikipedia.org/wiki/Phased_array_ultrasonics
  8. ^ Birring, Anmol (September 2008). “Selection of Phased Array Parameters for Weld Testing”. Materials Evaluation.
  9. https://www.zetec.com/blog/phased-array-vs-radiography-examining-the-advantages-of-paut/