PHASED ARRAY & TOFD TRAINING
ULTRASONIC PHASED ARRAY
Ultrasonic PAUT inspection offer greater probability of detection due to its capability of variable beam angle scanning capability and the beam steering feature enables superior detection ability of discontinuities in single sweep.
Ultrasonic phased arrays is an advanced techniques that use a multiple element probe whereby the output pulse from each element is time delayed in such a way so as produce constructive interference at a specific angle and a specific depth.
These time delays can be incremented over a range of angles to sweep the beam over the desired angular range.
For example, 40 to 75 degree beam sweep would be produced by calculating the time delays to produce constructive interference at 40, 41, 42 …75 degs.
This NDT technology is also referred as Swept Beam Ultrasonic testing.
ADVANTAGES OF ULTRASONIC PHASED ARRAYS:
- Phased arrays allow real-time control of three important ultrasonic probe parameters
- Focal distance: continuously and dynamically adjustable
- Beam angle: continuously and dynamically adjustable
- Focal spot size: dynamically adjustable
- Extra benefit
- Multiplexing allows fast displacement of ultrasonic beam within probe
- Main benefits of ultrasonic phased arrays
- High-speed inspection using single-axis scans instead of conventional raster scan
- Near-optimal focal length and focal spot for various areas of complex parts or thick components
- Small, simple probe assembly with multiple beams from a single probe
- Easy-to-install, one-axis scanning systems
TIME OF FLIGHT DIFFRACTION (TOFD)
TOFD (Time of Flight Diffraction) technique is a computerized and automated system for weld inspection which is able to scan, store, and evaluate indications in terms of height, length, and position with a grade of accuracy never achieved by other ultrasonic techniques.
TOFD has two blind zones where it is not sensitive to defects; hence TOFD needs to be supplemented by a conventional pulse-echo examination of the near and far walls.
Time-of-flight diffraction (TOFD) is a sensitive and accurate method for the nondestructive testing of welds for defects. TOFD originated from tip diffraction techniques.
In a TOFD system, a pair of ultrasonic probes sits on opposite sides of a weld. One of the probes, the transmitter, emits an ultrasonic pulse that is picked up by the probe on the other side, the receiver.
In undamaged pipes, the signals picked up by the receiver probe are from two waves: one that travels along the surface and one that reflects off the far wall. When a crack is present, there is a diffraction of the ultrasonic wave from the tip(s) of the crack.
Using the measured time of flight of the pulse, the depth of a crack tip can be calculated automatically by simple trigonometry.
- A computerised and automated system for weld inspection.
- Probes are mounted on a buggy that travels along a weld, recording data as it moves.
- Compared to conventional methods of ultrasonic testing, TOFD is sensitive to cracks and measures their dimensions accurately.
- TOFD has two blind zones where it is not sensitive to defects, hence TOFD ought always to be supplemented by a conventional pulse-echo examination of the near and far walls. The pulse echo probes are commonly mounted on the same buggy as the TOFD probes.
- Requires ultrasound technicians with advanced training.