Phased Array Ultrasonic Testing (PAUT)
Phased Array Ultrasonic Testing (PAUT) is based on the same physics as the Conventional Ultrasound inspection. The differences are mainly the probe technology and configuration as well as the acquisition instrument electronics. A Phased Array probe typically consists of 16 to 128 individual elements and can be customized to include more or fewer elements. The elements can also be arranged in linear, matrix and annular patterns.
Possible Phased Array configurations are dependent on what the probe and electronics are capable of. Each element is controlled individually, therefore allowing for the generation of a customized ultrasound beam using a defined delay.
Depending on the inspection requirements, it is possible to optimize each of the essential parameters, such as angular opening, beam orientation, focusing, sectorial scanning and linear scanning.
- Better coverage of the area of interest than with a single probe and wedge;
- Increased Probability of Detection (PoD) during weld inspection;
- Detection of both embedded flaws and surface connected ones;
- Increased production of resulting data;
- Encoding and data recording for future analysis/record-keeping;
- Real time imaging of the inspection area from multiple perspectives;
- Better flaw characterization and sizing with the availability of advanced software tools
- Better repeatability;
- Lightweight and safe;
- Compatible with other inspection methods such as 3D scanning and Eddy Current.
Automated Ultrasonic Testing (AUT)
Automated Ultrasonic Testing (AUT) consists of a motorized inspection system (the scanner), which manipulates the probes while tracking their position the entire time.
Thanks to recent innovations in both software and robotics, AUT systems equipped with multiple PAUT probes, cameras, and sensors are now available.
One of the first applications in which this technique achieved worldwide acceptance and deployment has been the inspection of pipeline circumferential welds in lieu of radiography. In this case, the scanner generally includes two PAUT probes, a pair of TOFD (Time-of-Flight Diffraction) probes, as well as two pairs of ‘transverse’ probes.
In addition to weld inspection, the AUT technique is ideal for corrosion detection on difficult to access structures. It can also provide 100% coverage with an increased production of resulting data in comparison to traditional methods.
- Increased production of recorded data with precise positioning;
- Simultaneous use of different probes (PAUT/TOFD/CUT) for an accurate evaluation of a discontinuity’s dimensions;
- Reduction in human error;
- Compatible with additional sensors (cameras, temperature probes, humidity sensors, etc.);
- Complete coverage of corroded areas with great consistency.
Conventional Ultrasonic Testing (CUT)
Conventional Ultrasonic Testing (CUT) uses a probe comprised of a piezoelectric element capable of deforming and generating high frequency acoustic waves that travel a specific velocity dependent on the material. The result is an A-scan on the UT instrument’s display. Analysis of this A-scan display allows for the evaluation and interpretation of the specimen under examination.
Conventional Ultrasonic inspection is primarily used for thickness measurement, weld inspection, and for lamination and corrosion detection. Multiple CUT modes exist: reflection (Pulse-Echo), Pulse-Receive (Dual) and Through Transmission (TT). Pulse-Echo is most common.
- Quick and cost efficient solution for thickness measurements;
- Live visualization of the measurement (A-Scan);
Time-Of-Flight Diffraction (TOFD)
Time-Of-Flight Diffraction (TOFD) is a technique based on an ultrasonic wave’s travelling time, or ‘time of flight’, and the diffraction produced by the extremities of the discontinuity. TOFD consists of a pair of CUT transducers on angled wedges defined to produce longitudinal waves. A pair of probes face each other: one pulses while the other receives, and are separated by a known distance that ensures coverage of the desired zone.
TOFD data analysis is performed with unrectified A-Scans and a B-Scan with a greyscale colour palette.
TOFD is recognized for its high level of accuracy and precision regarding sizing and is often used as a complement to the Phased Array method.
- High level of accuracy and precision;
- Live display of the results;
- Single scan required to cover weld’s complete volume;
- High level of sensitivity.
Guided Wave (GW)
Guided Wave (GW) inspection is an NDT method based on low frequency ultrasonic waves travelling along great distances with little loss of energy. Detection of corrosion or welds can be performed up to a range of 90m (300’) on either side of where the collar (containing the probes) is positioned.
In addition to being able to cover great distances, Guided Waves can be used to inspect pipes that are not accessible to other NDT methods; this method can be used to inspect buried, isolated or coated pipes.
- Can inspect extensive lengths from a single position;
- Can reach inaccessible areas;
- No production downtime;
- No need to remove pipe isolation or coating.
Full Matrix Capture (FMC)
Full Matrix Capture (FMC) is an advanced data acquisition and reconstruction method using PAUT probes. FMC is based on the synthetic focusing principle and is processed by algorithms resulting in a picture-like visualization of the area under examination.
The basic operation behind the method is that each element of the entire probe aperture emits an ultrasound in the material while all the elements record the returned signal. All this data is then processed and received signals are organized as a matrix.
The resulting matrix can be processed by algorithms to produce the image. This process is called the Total Focusing Method (TFM).
The data reconstruction happens on a defined zone where each point is constructed from the information recorded by each probe element while taking the various delays into consideration. TFM comes in multiple modes depending on the nature of the reflected ultrasonic wave, which is designated by a combination of the letters T (transverse) and L (longitudinal): TT, TTT, TTL, LLL, etc.
- Increased resolution of the indications with great definition and a picture-like image;
- Better characterization of the indications;
- Increased signal-to-noise ration compared to standard PAUT;
- Better representation of the profile of a corroded surface.