What is Phased Array Ultrasonic Testing?

How well do you know the working principles of phased array ultrasonic testing?

The answer to this question is well applicable to both newbies and veterans in the non-destructive testing industry. 

Phased array ultrasonic testing is a testing technique that utilizes distinctive multi-element array transducers, which uses these elements severally in a modeled progression referred to as phasing. This phasing progression permits wave focusing, steering, and scanning, and it is usually executed automatically.

To further expound on this phenomenon, join us on this fascinating journey into the world of non-destructive testing techniques. We are set if you are.

I. What is Phased Array Ultrasonic Testing?

As briefly explained above, Phased Array Ultrasonic Testing (PAUT) is a modern non-destructive inspection technique that uses a set of ultrasonic testing (UT) probes made of various tiny elements, with each component pulsed independently with automated programming referred to as phasing. 

When different downtimes stir these elements, the beams can be maneuvered at different points, focused at a different distance inward, or bi-directional above the length of a long array, which creates the electronic movement of the beam. 

Also, Phased array probes can be manually deployed in an independent working mode scrubbing the exterior of a component, tethered to an encoder to document position, or placed on a semi-automated or computerized scanner for excellent productivity.

➤ Related Article: Difference: PAUT v.s. TOFD

➤ Related Article: Comparison Guide: UT v.s. PAUT

II. Features of Phased Array

Now that we have a better understanding of the phased array ultrasonic testing, let’s consider some of the features of the non-destructive testing method.

• Firstly, as clearly stated, phased array ultrasonic testing is an advanced inspection technique that is deployed as a measure in quality control and assessment.
• The size of the focal spot is reliant on probe active wavelength, aperture, and focal length, and this could restrict focus on the near field of the phased array probe.
• Numerous probe elements generate a steady beam.
• And lastly, as compared to conventional testing, a phased array can be pretty intricate and costly. 

III. What is Phased Array Ultrasonic Testing Used for?

Phased array ultrasonic testing is an essential tool used in various inspection cases. However, the most popular uses of this testing method are highlighted below. 

• Weld Inspection – phased array ultrasonic testing is suitable for this type of flaw because it helps detect porosity, slag inclusions, and lack of fusion, especially in pressure vessels, tubing, and piping which as well could make any equipment hazardous and life-threatening.

• Crack Detection – phased array ultrasonic testing is utilized for the detection of cracks such as Inside Diameter and Outside Diameter cracks (I.D/O. D cracks), Stress Corrosion Cracks (SCC), Hydrogen Induced Cracking (HIC), and Stress Oriented Hydrogen Induced Cracking (SOHIC). 

• Thickness Measurement – phased array ultrasonic testing is applicable for testing diminished thickness that affects any manufacturing industry. When there is a defect irrespective of how minute, Phased array testing can help diminish any structural integrity to any component if deployed accurately.

• Corrosion Mapping – the introduction and infusion of phased array ultrasonic testing has helped detect corrosion damages such as pitting. With such a testing technique, there is a guarantee of a successful corrosion mapping inspection with certainty that all areas of interest have been entirely covered. These testing techniques boost the lateral ratio resolution against surface scanned speed.

• PAUT and TOFD Standard Calibration Blocks – calibration blocks help ascertain the thickness of required welding thickness which phased array ultrasonic testing helps to achieve.

IV. Flaws that Phased Array can Detect

Phased array ultrasonic testing (PAUT) is an extensively adopted modern testing method for non-destructive testing (NDT) in numerous industrial sectors, such as power generation, construction, and pipelines. 

This technique is widely deployed to detect discontinuities such as cracks and defects that ascertain component quality. And because of the ability to determine the specifications such as beam angle and focal distance. This method is highly productive regarding detecting defects and speed of testing.

Phased array ultrasonic testing is also appropriate for testing corrosion defects and wall thickness measurements as part of the flaws detectable by this non-destructive testing technique. Therefore, industrial flaws that can be detected by employing phased array ultrasonic testing method includes: 

• Corrosion inspection
• Inspection of welds such as porosity and slag inclusions (piping, tubing, and pressure vessels)
• Detection of cracks such as Stress Corrosion Cracks (SCC), Hydrogen Induced Cracking (HIC), and Stress Oriented Hydrogen Induced Cracking (SOHIC)
• Rolling stock inspection (axles and wheels)
• Thickness measurement

V. What is the Working Principle of Phased Array Ultrasonic Testing?

As mentioned above, phased array ultrasonic testing probes consist of several piezoelectric crystals that transmit/receive independently at different intervals. An ultrasonic beam is centered using time delays, which are employed to the elements to enkindle a constructive interference in the wavefronts. This interference permits the energy to remain focused at any depth and point in the test samples.

Each element emits a circular-shaped wave at a stipulated time, emitting waves that merge and split to generate an almost direct wavefront at the designated location. Alternating the progressive downtime allows the beam to be maneuvered electronically and permeates the test material like a beacon. A visual image is generated when numerous combined beams display a section through the test object.

VI. Advantages and Disadvantages of Phased Array Ultrasonic Testing 

Phased array ultrasonic testing is packed with many advantages over other forms of quality assessment tests. On the other hand, it has also been found to have some shortfalls, enumerated below. 

Advantages of Phased Array Ultrasonic Testing

• Speed: fast scope of bigger exteriors translates that Phased Array Ultrasonic Testing can routinely be performed a lot faster than regular Ultrasonic Testing.
• Repeatability:  Phased Array Ultrasonic Testing can conveniently be deployed for recurrent scans because of its high consistency and accuracy.
• Accuracy:  Accurate and comprehensive cross-section of a test object is achieved when phased array ultrasonic testing is deployed, which assists in detecting defects through the discharge of beams at different points consecutively.
• Coverage:  Another advantage of Phased Array Ultrasonic Testing is its coverage on a test object. Directing, channeling, and scanning a test object via phased array testing techniques allows the transducer beams to inspect a bigger or wider surface area faster and with a clearer or higher resolution. 
• Safety:  To reduce the risk of exposure to the inspection officers, a semi-automated or computerized Phased Array Ultrasonic Testing is an adequate replacement for radiographic testing and extinguishes any safety endangerment associated with radiography.
• Flexibility: PAUT is also very useful in an environment with little to no access to mechanical testing or scanning. This is possible because of its flexibility, as its beam can glide over a test material for accuracy and precise inspection.

Disadvantages of Phased Array Ultrasonic Testing

As advantageous as it is, it has a few drawbacks, and some of its drawbacks are highlighted below.

• Training: Phased Array Ultrasonic Testing usually needs extra training by inspection personnel to operate effectively and for accurate inspection findings.
• Cost: Phased Array Ultrasonic Testing may require a larger investment in tool acquisition and personnel training than traditional ultrasonic testing. But in the long run, all of its initial costs would be counterpoised considering its flexibility and time saved in inspecting test objects.

Conclusion

In conclusion, phased array ultrasonic testing is an ultrasonic testing technique that utilizes distinctive multi-element array transducers that permit wave focusing, directing, and scanning, usually executed automatically.

Furthermore, phased array ultrasonic testing is deployed as a measure of quality assessment and control, and the size of its focal spot is determinant on the wavelength, focal length, and aperture.

Consequently, its efficacy is evident in its capacity for corrosion inspection, thickness measurement, an inspection of welds such as porosity and slag inclusions, etc. 

Finally, phased array ultrasonic inspection is very advantageous compared to the other conventional testing techniques, and they include flexibility, safety, speed, accuracy, coverage, and repeatability. Although it also has a few disadvantages, these disadvantages could be made up for in the long run.