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Can PAUT Replace RT?

Sep. 19, 2022

PAUT is making its debut in the field of medical imaging and falls under the category of ultrasonic testing (UT) for non-destructive testing. It is a more advanced technique that uses the same basic principle of emitting ultrasound waves onto a surface to collect data. "Phased" refers to the timing component of a PAUT, and "array" refers to the use of multiple ultrasonic emitters.


In contrast to the use of probes with a single element and a fixed angle in a conventional UT, a phased array UT uses probes consisting of multiple elements and a series of angles that are synthesized by pulse control. These piezoelectric elements are programmed to pulse individually at a calculated time, with the time delay between pulses depending on a number of factors including asset geometry and acoustic properties. Once the control sequence is defined and programmed, the ultrasonic pulses are emitted at different angles, allowing them to be resized, scanned, and steered to provide a 'sliced' image view, potentially revealing hard-to-detect cracks or other defects in the asset, or to obtain thickness measurements during corrosion testing.


As ultrasonic pulses are synthesized electronically from any element in the array, any combination of pulse and reception techniques can be constructed to suit this situation. This has given rise to more advanced techniques such as Full Matrix Capture (FMC) or Total Focus Method (TFM).

HS 1020 Ultrasonic Bolt Stress Detector

HS 1020 Ultrasonic Bolt Stress Detector


The many advanced advantages of PAUT over conventional UT include the following.

  • Extreme detail and large data collection. the PAUT transducer beam can be resized, angled, and steered to allow very detailed mapping or sector scanning. Large amounts of high-resolution data can be stored, therefore allowing the user to record better.


Higher probability of detection (POD) Thanks to its comprehensive data capture and more complete testing, POD is a significant improvement over classical methods.


  • Faster. The PAUT is often faster than conventional single probe UTs due to the ability to cover assets quickly. The beam angle is adjusted by software rather than manually.


  • Consistency. Repeat scanning is easy to perform due to its high accuracy.


  • Easy to use on small or complex surfaces. If there is insufficient space for mechanical scanning, the "scanning" nature of the PAUT (the probe does not move backwards and forwards) makes it particularly useful on difficult-to-scan surfaces that may have complex shapes or geometries.


  • Eliminate safety hazards. The use of a PAUT supporting a robot eliminates the need for scaffolding or rope access and prevents employees from being exposed to potentially harmful substances or high temperatures.

Multi-function Phased Array Ultrasonic Flaw Detector HS PA20-Aex

Multi-function Phased Array Ultrasonic Flaw Detector HS PA20-Alex


For safety reasons, PAUTs are increasingly being used as an alternative to radiographic inspection (RT) for a number of reasons, including the significant advantage of not being exposed to the risk of radiation.


PAUT vs radiography

Increasingly used for industrial inspection, PAUT offers many of the same benefits compared to RT; perhaps most importantly a safer alternative.


As can easily be seen from its title, RT inspection uses an X-ray or gamma ray generator to direct the beam to the asset. As the beam penetrates the surface, the image is captured on film and the subsequent development of the negative produces a 2-D image (or 3-D, following a computed tomography scan).


It is well known that in the medical field, improper exposure to radiation can cause harm to radiographers, other staff, and the public. Therefore, during radiographic testing, personnel must be evacuated from the testing site and all work in the surrounding area must be stopped until the testing is complete. In addition, radiography requires additional personnel to ensure the safety of the workplace. This means higher costs, not only because of the extra labor but also because of the loss of work being done around the test area.


TOFD Flaw Detector

TOFD Flaw Detector

With the PAUT, however, work around the test area can be carried out as usual. While PAUT equipment is easy to transport and the results are immediate, RT films must be developed and may take longer, depending on the valve and thicker material.  


Both PAUT and RT are capable of detecting discontinuities or defects with high POD, RT has limited ability to detect weld defects - for example, unfusion. While the PAUT is able to handle smaller volume defects, it is able to penetrate thicker materials.


Employees are becoming more familiar with the PAUT as these inspections can be complex and are an investment when considering training; therefore, radiography has a high percentage of qualified personnel. However, depending on the location where the tests are carried out, RT requires certification and/or licensing or special training.


In summary, both processes require experienced operators to ensure the accuracy of data reading and result interpretation. While RT may make more sense in some cases, PAUT (which is safer, faster and produces more complete, higher resolution data) is increasingly becoming the choice for asset inspections.

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