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Automated Ultrasonic Testing

Automated Ultrasonic Testing (AUT) is a fully automated technique that utilizes a multi-channel ultrasonic imaging system and encoded robotic scanners to perform a UT examination on a piece of equipment. AUT is used in a number of industries and can be an effective method for inspecting a number of different types of equipment.


AUT works similar to traditional ultrasonic testing (UT), although there are several important differences. Like traditional UT, the process works by emitting ultrasonic waves into a piece of equipment. These waves will then travel through the part until they reflect off either the opposite wall, or any defects they encounter. Once the wave returns to the near wall, the time it took them to return can be measured, which can be used to determine if there are any cracks or defects inside the material.

Unlike traditional UT, AUT is run automatically without the need for inspector control. An AUT device is attached to the part using magnetic wheels. It then moves along the part as it emits and receives ultrasonic pulses.


AUT can be used to inspect pressure vessels, piping, storage tanks, spheres, and other equipment while in service for potential damage. AUT offers a full volumetric inspection providing details on shell material degradation such as erosion, corrosion, hydrogen blisters, hydrogen induced cracking (HIC), and related interlinking cracking.

This system can also be utilized in weld inspection for detecting both service and fabrication related defects implementing the pulse-echo or Time of Flight Diffraction (TOFD) techniques.


AUT has a number of advantages when compared to other forms of nondestructive testing.

  • The major advantage of AUT is that it provides detailed inspection data at a high rate of speed with exceptional accuracy and repeatability.

  • It also allows for in-service examinations of equipment at elevated temperatures (Up to 300º F with direct scanner contact).

  • AUT allows for high-speed data acquisition; sometimes as fast as up to 20 inches per second. In some cases, AUT can be used to satisfy internal inspection intervals in lieu of confined space vessel entry.

  • This method can provide detailed information in a fitness for service evaluation.

  • AUT has exceptional accuracy and repeatability. It’s encoded scanning is accurate to .001 inches. This makes it excellent for tracking the growth of a defect over time and plan maintenance activities around it.

  • AUT provides multi-tasking capabilities which utilize a full array of transducers simultaneously.

  • AUT is cost efficient and allows facility owners to optimize their inspection dollar.

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Phased Array Ultrasonic Testing

Phased Array Ultrasonic Testing (PAUT) is an advanced NDT method that is often used for weld inspection and crack detection. It can also be used to effectively profile remaining wall thickness in corrosion survey applications.

PAUT works by activating several elements independently, each emitting an ultrasonic pulse. The pulses form a pattern of constructive interference, which causes the overall angle of the beam to be focused in a set direction. By pulsing the elements in different ways, the beam can be steered and swept electronically, without having to move the phased array probe.

           Phased array probes typically consist of a transducer assembly with anywhere from 16 to as many as 256 small individual elements, each pulsing separately. The frequency of these pulses can range anywhere from 2MHz to 10MHz. A PAUT consists of a computer-based instrument that is capable of driving the multi-element probe, receiving and digitizing the returning echoes, and plotting that echo information in various formats.

  • Pressure vessels: testing of nozzle, circumferential and longitudinal seam welds.

  • Piping: testing of in-service or newly fabricated piping in accordance with applicable codes.

  • Structural Steel: weld quality verification.

  • Wind turbine towers: weld quality verification during the fabrication process and inspection of erected towers.

  • Corrosion mapping: C-Scan examinations on areas where obstructions are present restricting most standard automated crawlers.

  • Crack sizing and detection: the detection of cracking on piping or components with the capability of continued monitoring for growth and propagation.

  • PAUT keeps a permanent record of the inspection as it is being performed so that the results can be stored and reviewed at a later date if need be. PAUT is code compliant and it has a better utilization of manpower compared to industrial radiography on shutdowns. Phased array testing is also highly repeatable.

  • Sentinel’s advanced technicians are equipped with the latest technology, minimizing downtime during execution. They provide and unparalleled experience and professionalism.

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Time of Flight Diffraction

Time of Flight Diffraction (TOFD) is an advanced method of ultrasonic testing. This technique is a sensitive and accurate method for the nondestructive testing of welds or defects.

TOFD is conducted from a system that is made up of two probes located on opposite sides of the weld. One of the probes is a transmitter which emits an ultrasonic pulse. The second opposing probe is the receiver, and it picks up the pulse. The probes are mounted on a movable cart, which uses a computer system to record data as it moves.

             In a weld without any flaws or damage, once the pulse is emitted from the transmitter, it will split into two waves. One of the waves is known as the lateral wave and it travels along the surface of the part. The second is called the back wall reflection, which reflects off the back wall of the part. Both are picked up by the receiver, which it uses as a baseline.

If a discontinuity is present, a diffraction of the emitted wave will appear from each tip of the crack. This means that the wave splits into two parts which are detected by the receiving probe. Once discovered using the measured time of flight, the pulse depth and location of the defect can be calculated by comparing the diffracted waves to the lateral wave and back wall reflection.

  • Utilized for rapid detection and sizing of cracking and weld flaws

  • Typically used on heavy wall reactors or vessels in lieu of industrial radiography

  • Can be combined with Phased Array to provide higher POD and more accurate classification of defects

  • The detection of cracking


TOFD is very sensitive to cracks and is able measure their dimensions and position accurately. It is also able to detect cracks regardless of their orientation.

In most cases, only one scan is required to find defects in a weld. This makes TOFD one of the fastest methods available for detecting defects in welds. This method also has a good degree of repeatability and gives consistent results. This means that if TOFD is used on the same weld over time, it is able to track the growth of flaws. It is also capable of precisely detecting and sizing many different types of defects within a weld.

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