Published on 08-Nov-2023

Phased Array Ultrasonic Testing: A Ultimate Guide

Phased Array Ultrasonic Testing: A Ultimate Guide

Table of Contents

  • Introduction
  • Evolution of Non-destructive Testing and PAUT
  • What is Phased Array Ultrasonic Testing (PAUT)?

  • How does PAUT Work?
  • Basic Principles of PAUT
  • The procedure of Phased Array Work
  • Parameters of Phased Array Work
  • Advantages  of Phased Array Work
  • Disadvantages of Phased Array Work
  • Applications of Phased Array Work
  • Phased Array Ultrasonic Testing Standards
  • Advantages of Phased Array Ultrasonic Testing (PAUT)
  • Applications of Phased Array Ultrasonic Testing (PAUT)
  • Future Trends in Phased Array Ultrasonic Testing
  • What is an Ultrasonic B Scan?
  • Conclusion
  • Key Takeaways
  • FAQs


When it comes to Non-destructive Testing (NDT) methods, Phased Array Ultrasonic Testing (PAUT) has emerged as a powerful and efficient technique.

Phased Array Ultrasonic Testing, as the name suggests, uses multiple transducers in an array inside the testing probe to manipulate the input ultrasonic beam by exciting them in various sequences that can be controlled digitally.

These Ultrasonic Transducers are made of piezoelectric materials that convert one form of energy to another to fulfill the probe's purpose.

Evolution of Non-destructive Testing and PAUT

Non-destructive Testing is an essential practice used to assess the integrity of materials and structures without causing any damage.

As industries advanced, the need for more sophisticated PAUT NDT Methods became evident.

This is where phased array ultrasonic testing came into play. 

What is Phased Array Ultrasonic Testing (PAUT)?

Phased Array Ultrasonic Testing is a modern NDT Technique that utilizes multiple ultrasonic elements to inspect materials.

Unlike conventional Ultrasonic Testing Methods, which use a single transducer to send and receive waves, PAUT test employs an array of elements.

Phased Array Ultrasonic Testing, as the name suggests, uses multiple transducers in an array inside the testing probe to manipulate the input ultrasonic beam by exciting them in various sequences that can be controlled digitally.

These Ultrasonic Transducers are piezoelectric materials that convert one form of energy to another to fulfill the probes’ purpose.

The sequenced actuation of the transducers facilitates sectorial, depth, and linear scanning.

It can also be used in situations where conventional Ultrasonic Testing methods are used.

It can be used for checking wall thickness profiles and Weld Inspection, as well as inspections of Heat Affected Zones (HAZ), which makes it versatile and viable across industries like manufacturing, construction, petrochemicals, and aerospace.

The input Ultrasonic Testing Procedure of the phased array ultrasonic testing apparatus is made to sweep across the testing subject and hence pick up on deformities that would have been missed by a conventional single-beam PAUT ultrasonic testing device that produces a singular directed beam.

How does PAUT Work?

In PAUT Inspection, each element in the array can be controlled individually.

By altering the timing and amplitude of the signals sent to each element, the ultrasonic waves can be focused, steered, and scanned electronically.

This allows for greater flexibility in inspecting complex geometries and varying materials.

Basic Principles of PAUT

Understanding the basic principles of PAUT is crucial to grasping its significance in the realm of Non-destructive Testing. Here are the basic principles of PAUT. 

1. Wave Interference

PAUT ultrasonic testing takes advantage of wave interference.

By controlling the phase array UT relationship between the elements in the array, constructive interference can be achieved, enhancing the amplitude of the ultrasonic waves at a specific focal point.

This results in better defect detection and accurate measurements.

2. Beam Steering

The ability to steer the ultrasonic beam electronically is a standout feature of PAUT testing.

Traditional Ultrasonic Testing requires physically moving the transducer to change the beam direction.

In PAUT testing, the basic principles of PAUT are crucial to grasp its significance in the realm of Non-destructive Testing. Here are the basic principles of PAUT. 

3. Multiple Angles and Frequencies

PAUT testing allows for the use of multiple angles and frequencies in a single scan.

This versatility enables inspectors to assess various aspects of the material's integrity in one go, reducing inspection time and increasing efficiency.

4. Sensitivity and Signal-to-Noise Ratio

With PAUT NDT Testing, the sensitivity and signal-to-noise ratio can be optimized.

This means that even small defects can be detected clearly amidst the noise, ensuring accurate assessment and minimizing the chances of false negatives.

5. Real-time Imaging

One of the most significant advantages of phased array testing is its ability to provide real-time imaging.

The dynamic visualization of the inspected area helps inspectors make immediate decisions, leading to quicker assessments and faster decision-making processes.

Procedure Of Phased Array Work

One of the most prevalent uses of phased array ultrasonic testing is to inspect welded regions for potential defects and discontinuities.

The procedure for a Weld Inspection would generally go as follows:

  • A skilled operator should thoroughly inspect the welded area and choose a frequency based on the thickness of the area. 
  • Positioning should be carried out with careful consideration of the heat-affected zone (HAZ) and the start of the weld with the start angle of impedance at the former and end angle at the latter region.
  • In cases where the end angle at the weld zone exceeds 60°, further scanning should be conducted (preferably line scanning).
  • The probe is affixed on an angular wedge, generating a shear wave in the testing material for analysis.
    The distance between the center of the weld zone and this wedge should be calculated mathematically or ray traced.
  • The testing zone should be covered by the angles covered by the probe.
  • To make a time-corrected gain graph with defects that were made artificially at known distances from the surface, you should use a test sample that is the same size and made of the same material.
  • A steady line guide for probe movement should be drawn on the surface to ensure steady movement along the test zone.
  • The probe can hence be moved along the line drawn, and testing can be carried out.

Parameters of Phased Array Work

With complex apparatus like that of the phased array Ultrasonic Testing Technology machine, a number of variables are present within the mechanisms of the testing unit.

These parameters affect the manner of analysis to be conducted on the test subjects, and a standard operating procedure can be created so every inspection performed can be conducted under similar test conditions and/or device settings.

The parameters that can be adjusted are as follows:

  • Probe adjustments can be made where the element width, number of elements, kerf, element length, pitch, and nominal frequency can be adjusted.
  • Wedge material, wedge material velocity, incident angle, and height of reference element can be inputted.
  • The type of scan, the number of focal elements in the incident beam, and the number of steps can be varied as per testing needs.
  • The scan pattern, test environment (immersed or physical contact), and test mechanics can also be inputted to adjust test results accordingly.
  • The couplant material, test material geometry, and velocities, along with the blocks used for calibration, are also important parameters that need to be considered before planning the test design.

Advantages Of Phased Array Work

Conventional single probe Ultrasonic Testing devices can be delicate and complex to use.

It also has many limitations when it comes to the size, geometry, and accessibility of test material.

For more complex inspections like welding, it can often prove to be detrimental and inaccurate.

The probability of false readings is reduced in a phased array probe as it can detect multiple signals simultaneously.

Phased array ultrasonic inspection also provides the following advantages:

  • It uncomplicates testing procedures by automating beam adjustments and digitizing the results.
  • It also eliminated the need for multiple calibrations of the individual probes as it uses a phased array of signals.
  •  Small, complex, and irregularly shaped test surfaces can often provide incorrect readings due to irregular reflection of the result beams.
  • Due to the controlled, adjustable input of multiple ultrasonic waves, these issues are 
  • The Phased Array Ultrasonic Testing machine's electronic scanning feature also gets rid of the need to re-configure it over and over again by hand, which greatly lowers the chance of mistakes.
  • This increases testing speed and saves labor hours.
  • Phased array ultrasound testing avoids the loss of coupling or potential changes to it by avoiding probe movement.
    The results thus obtained are reliable and consistent.

Disadvantages of Phased Array Work

Phased array ultrasonic testing provides numerous benefits as an Advanced Non-destructive Testing Methodology.

However, it also poses disadvantages, such as:

  • Phased Array Ultrasonic Testing cannot be used for a variety of materials and operations, such as surface defects, defects caused by cyclic tensile loadings like bolts and tubes, etc.
  • Sectorial scanning also poses the risk of providing an unsatisfactory angle of incidence for the beam.
  • Skilled labor is required to operate this apparatus, as it comprises a complex array of transducers and multiple data management and manipulation features that need skill and experience to utilize the PAUT efficiently.
  • Being an advanced device, the phased array ultrasonic testing apparatus is expensive to purchase compared to conventional Ultrasonic Testing Methods.
  • As per the American Welding Society's bridge-welding cost (AWS D1.5), phased array Ultrasonic Testing Applications are not recognized as an official inspection technique.
    Hence, ultrasonic testing for welds and steel is not used frequently in the bridge fabrication industry. 

Applications of Phased Array Work

Phased Array Ultrasonic Testing is used in the offshore Oil and Gas Industry, offshore wind power generation industry, shipping, shipbuilding and repair, mega yachts and luxury boating industry, civil engineering, steel construction and machine building industries, process building, and many more such fields.

This makes it incredibly flexible across industries and modern-day technology.

The PAUT can also be used for:

  • Time of flight diffraction (TOFD) calibration blocks to rectify and confirm the required test setup.
  • Phased Array Ultrasonic Testing calibration blocks to characterize input beams
  • To assess the structural integrity of Pressed vessels to ensure safety during operation.
  • PAUT can also be used to measure the thickness of test subjects.
  • It can be used to assess composite materials.
  • To inspect for corrosion on a sub-surface.
  • The phased array ultrasonic apparatus is also used in railways to inspect the rolling stock wheelset.

Phased Array Ultrasonic Testing Standards

Industries that use Non-destructive Testing Techniques, such as phased array ultrasonic testing, require uniformity to gauge the status of structures and materials tested correctly.

Some standards used for PAUT studies include:

  • American Society for Testing and Materials-“Standard Practice for Contact Ultrasonic Testing  of Welds Using Phased Arrays”- E2700-09
  • American Society for Testing and Materials-“Standard guide for evaluating characteristics of phased array ultrasonic examination and  Systems”-E2491-06
  • American Society of Mechanical Engineers - “Use of Ultrasonic Examination in Lieu of Radiography”-2235-9
  • American Society of Mechanical Engineers- “Case of ASME Boiler Pressure Vessel Code. Use of Manual Phased Array Escan Ultrasonic Examination per Article 4 Section V”- 2558

Advantages of Phased Array Ultrasonic Testing (PAUT)

PAUT offers a plethora of advantages that make it a preferred choice in the realm of non-destructive testing, with many Applications for Underwater Ultrasonic Testing.  

Let's delve into these advantages and understand why PAUT stands out in the Flaw Detection and Inspection Processes.

1. Enhanced Imaging

One of the standout advantages of PAUT is its capability to provide enhanced imaging.

By precisely controlling the timing and amplitude of ultrasonic signals sent to each element in the array, PAUT can focus and steer the ultrasonic beam.

This results in high-resolution images that accurately depict the internal structure of the materials being inspected.

These detailed images facilitate better visualization of defects, allowing inspectors to identify even the smallest irregularities.

2. Improved Flaw Detection

PAUT's ability to manipulate ultrasonic waves through phase control contributes to improved Flaw Detection.

By optimizing wave interference, PAUT enhances the amplitude of ultrasonic waves at specific focal points.

This sensitivity amplification aids in detecting even minor flaws and defects that might go unnoticed using conventional testing methods.

3. Accurate Sizing and Depth Determination

Accurate sizing and depth determination of defects are paramount in Non-destructive Testing (NDT).

PAUT excels in this aspect by providing precise measurements of defect dimensions and depths.

The ability to control the beam's angle and focus allows inspectors to accurately assess the size and extent of flaws within the material.

This information is crucial for evaluating the severity of defects and making informed decisions about repair or replacement.

4. Data Acquisition Speed

In the fast-paced industries of today, efficiency is a key factor.

PAUT shines in this regard with its rapid data acquisition speed.

Traditional Ultrasonic Testing Methods often involve manual transducer movement and adjustments, which can be time-consuming.

PAUT's electronic manipulation of the ultrasonic beam eliminates the need for physical movement, enabling quicker and more efficient inspections.

This increased speed not only saves time but also allows for more comprehensive testing coverage.

Applications of Phased Array Ultrasonic Testing (PAUT)

Phased Array Ultrasonic Testing (PAUT) has found its way into a wide array of industries, each benefiting from its advanced capabilities in flaw detection and material inspection.

Here are some of the prominent applications where PAUT plays a key role.

1. Weld Inspection

Weld Inspection is a critical process in industries such as manufacturing, construction, and aerospace.

PAUT excels in this application by providing accurate and detailed assessments of weld integrity.

Its ability to manipulate ultrasonic waves and focus the beam ensures thorough coverage of welds, including those in complex geometries.

Especially during Ultrasonic Testing on tanks/pipelines.

PAUT detects defects such as cracks, porosity, and lack of fusion, helping maintain the structural integrity of welded components.

2. Corrosion Mapping

Corrosion is a common challenge in industries like oil and gas, marine, and infrastructure.

PAUT's proficiency in Corrosion Mapping is invaluable for assessing the extent and severity of corrosion in various materials.

By scanning the surface and subsurface layers, PAUT identifies corrosion-related anomalies and provides real-time imaging of affected areas.

This information aids in preventive maintenance and decision-making, minimizing the risks associated with corrosion-related failures.

3. Composite Materials

The use of composite materials is on the rise in industries like Aerospace Industry, automotive, and sports equipment.

However, inspecting these materials for defects can be challenging due to their complex nature.

PAUT addresses this challenge by offering precise inspections of composite structures, ensuring their integrity and performance.

Its ability to tailor the ultrasonic beam to different angles and frequencies makes it suitable for detecting defects like delaminations, voids, and fiber misalignments.

4.  Aerospace and Turbine Blades

The Aerospace Industry demands the highest level of safety and reliability.

PAUT meets these requirements by inspecting aerospace components, including turbine blades.

The intricate geometry of turbine blades makes conventional inspections challenging.

PAUT's electronic beam steering allows inspectors to assess these components without disassembly.

By detecting internal flaws, cracks, and defects, PAUT contributes to the overall safety and efficiency of aerospace operations.

Future Trends in Phased Array Ultrasonic Testing 

As technology continues to advance, the field of Non-destructive Testing is evolving rapidly.

Phased array ultrasonic testing is poised to play a significant role in shaping the future of inspections and flaw detection.

Here are some of the anticipated trends that will influence the landscape of PAUT in the years to come.

1. Miniaturisation of Equipment

One of the trends in PAUT is the miniaturization of equipment.

As technology becomes more compact and portable, PAUT devices are expected to follow suit.

Smaller and lighter equipment will enhance the mobility of inspectors, allowing them to perform inspections in challenging and confined spaces more efficiently.

This trend will particularly benefit industries like aerospace, where accessibility to intricate components is crucial.

2. Integration of Artificial Intelligence (AI)

The Integration of Artificial Intelligence is set to revolutionize PAUT.

AI algorithms can analyze complex data patterns and provide insights that might not be easily discernible to human inspectors. 

By incorporating AI-driven analysis, PAUT can improve defect detection accuracy and reduce false positives. 

This advancement will streamline the decision-making process and enhance the overall efficiency of inspections.

3. Automated Robotic Inspections

Automation is gaining prominence in various industries, and PAUT is no exception.

Robotic systems equipped with PAUT capabilities can autonomously navigate and inspect structures, reducing the need for human intervention.

These systems can be employed in hazardous environments, underwater inspections, and other scenarios where human access is limited.

Automated inspections will save time, enhance safety, and provide consistent results.

4. Advanced Materials and Complex Geometries

The future of PAUT will involve adapting to the increasing use of advanced materials and complex geometries.

As industries explore innovative materials and intricate designs, PAUT techniques must evolve to accommodate these changes.

5. Real-Time Data Sharing and Collaboration

In a digitally connected world, real-time data sharing and collaboration will become integral to PAUT practises.

Inspectors can remotely share inspection data and findings with experts and colleagues for immediate analysis and decision-making.

This trend will enhance the speed of problem resolution and enable real-time adjustments to inspection strategies.

6. Enhanced Visualisation Technologies

Advancements in visualization technologies, such as augmented reality (AR) and virtual reality (VR), will transform the way inspectors interact with PAUT data.

AR and VR interfaces can provide immersive visualizations of inspection results, allowing inspectors to navigate through internal structures and defects in a more intuitive manner.

This trend will enhance the understanding and interpretation of inspection data.

What is an Ultrasonic B Scan?

Ultrasonic B Scan is a powerful imaging technique that uses high-frequency sound waves to visualize and inspect objects beneath surfaces.

It's like creating an ultrasound image for machines and structures, similar to those used in medical settings. 

Ultrasonic B Scan uses multiple ultrasonic elements to sweep and focus sound waves, enhancing the accuracy and efficiency of flaw detection in materials.

It has evolved significantly since its inception in the early 20th century, revolutionizing the way we inspect and assess the integrity of structures.

It is used in industrial inspections for inspecting welds, pipelines, and critical components, and in medical diagnostics for early detection of medical conditions. 

Ultrasonic B Scan offers faster results, increased accuracy, and the ability to inspect complex geometries with ease.

As technology advances, it holds exciting possibilities, including improved imaging resolution and more portable and user-friendly devices.


Phased array ultrasonic testing is a Non-destructive Testing Technique that offers accurate and efficient inspection solutions across various industries.

Its advanced capabilities include wave interference, beam steering, multiple angles, sensitivity optimization, and real-time imaging.

PAUT's advantages extend beyond inspection, including enhanced imaging, improved flaw detection, accurate sizing, and rapid data acquisition speed.

As technology evolves, PAUT's applications will expand further, solidifying its position as a cornerstone of modern Non-destructive Testing practices.

As technology continues to evolve, PAUT will continue to contribute to safety, quality, and reliability across various sectors. Visit OnestopNDT for more insights on NDT. 

Key Takeaways

  • Phased Array Ultrasonic Testing is a powerful and efficient Non-Destructive Testing Method used for assessing material integrity without causing damage.
  • PAUT uses multiple transducers in an array to manipulate the input ultrasonic beam digitally, allowing for versatile inspections in various industries.
  • The technique facilitates sectorial, depth, and linear scanning, making it applicable in situations where Ultrasonic Testing Methods fall short.
  • PAUT's basic principles include wave interference, beam steering, the use of multiple angles and frequencies, sensitivity optimization, and real-time imaging.
  • The procedure for PAUT involves careful inspection of the material, selection of frequencies, positioning, and systematic scanning using an angular wedge.
  • PAUT parameters like probe adjustments, wedge details, scan patterns, and test environments can be tailored for specific testing needs.
  • Advantages of PAUT include enhanced imaging, improved flaw detection, accurate sizing, and automation, leading to increased efficiency.
  • Disadvantages include limitations in material applications, the need for skilled operators, and the higher cost compared to conventional methods.
  • PAUT finds applications in various industries, such as oil, and aerospace,  and is particularly useful for weld inspection and composite material assessment.
  • Future trends in PAUT include the miniaturization of equipment, adaptation to advanced materials, and enhanced visualization technologies.


Q. What is the PAUT inspection technique?

A: Phased Array Ultrasonic Testing is a non-destructive testing (NDT) technique that uses multiple ultrasonic elements and electronic time delays to create beams of ultrasound that can be steered, scanned, and focused electronically.

This allows for the inspection of materials in a more versatile and efficient manner compared to traditional ultrasonic testing methods.

Q. What are the two types of UT?

A: There are two main types of Ultrasonic Testing (UT):

1. Contact Testing:

Involves direct contact between the transducer and the material being tested. This is suitable for solid materials.

2. Immersion Testing:

Involves immersing the transducer and the material in a liquid couplant. This is often used for testing irregularly shaped objects or materials with complex geometries.

Q. Why use a phased array transducer?

A: Phased array transducers offer several advantages in ultrasonic testing, including:

  • Beam Steering: The ability to electronically steer and focus the ultrasound beam, allowing for better coverage and adaptability during inspections.
  • Multiple Angles: The capability to inspect a range of angles simultaneously increases the efficiency of the testing process.
  • Versatility: Suitable for inspecting complex geometries and varying materials with different acoustic properties.

Q. What is the main disadvantage of a phased array transducer?

A: One potential disadvantage of phased array transducers is their higher initial cost compared to traditional ultrasonic testing equipment.
     The technology and electronics involved in phased array systems can be more complex and sophisticated, leading to a higher upfront investment.

Q. What are the four types of transducer arrays?

A: There are various types of transducer arrays used in ultrasonic testing, including:

  • Linear Array: Elements are arranged linearly, allowing for inspection along a straight path.
  • Convex Array: Elements are arranged in a curved pattern, suitable for inspecting curved surfaces or materials with a radius.
  • Phased Array: Utilises multiple elements with controlled phase shifts for beam steering and focusing.
  • Annular Array: Elements are arranged in a circular pattern, providing the capability to focus and steer the beam in multiple directions from a central point.



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Application Notes