Phased Array Ultrasonic Testing (PAUT) is one of the most widespread methods used in Non-Destructive Testing. Phased arrays are used for various material inspections for cracks, voids, and pits caused by corrosion. Standard phased array testing uses focused ultrasonic beams using probes to measure the interiors of solid objects, including metals and composites. Although PAUT is faster and more effective than traditional NDT methods, it is not immune to shortcomings. PAUT summarises scans to form a single report. However, compiling data may lead to data loss from raw scans.
Neglecting scan data loss in standard PAUT can prove a costly mistake.
The Total Focusing Method algorithm, on the other hand, does not summarize. Information from each transmitter/receiver is digitized and stored independently, a process known as Full Matrix Capture (FMC). The software calculates a focal law for each pixel in the frame based on this information. This process is called ‘TFM acquisition.’ Using the TFM focal laws, each scan displays the image in high resolution.
The Total Focusing Method is not a replacement for your PAUT inspection but a healthy addition to the process. Standard PAUT does not work well with complex geometries, multiple acoustic interfaces, and material properties at different temperatures. PAUT imaging may not detect issues like hydrogen-induced cracking, high-temperature hydrogen attack, and dissimilar metal welds.
What TFM does for your Phased Array Ultrasonic Testing:
Using the Total Focusing Method means acquiring refined images with flaws more minor than 0.1mm. In some challenging applications, operators need to analyze raw A-scan data directly. Once scan data is assembled, the regular PAUT software erases raw data. When utilizing TFM for examination, however, each raw scan data is available in full resolution.
Using TFM acquisition to identify faults early on helps managers schedule repairs or replacements ahead of time, guaranteeing the most effective use of maintenance resources. Ultrasonic testing equipment that supports FMC and TFM is often more powerful. It goes beyond ordinary PAUT code compliance to provide thorough recordkeeping by preserving raw data for defect characterization.
The principal advantage of TFM is that the entire image is displayed with focused amplitude, compared to an image produced with PAUT, which is only highly resolved in the focal area of the beam.
The synthetic beam forming performed only on the receiving end in conventional PAUT is also done in the transmission phase in TFM to make the acquisition rate acceptable for NDT applications. The synthetic beam forming requires the application of specific delays on elementary A-scans acquired through FMC. Note that the FMC data set can provide basic data to any synthetic beam forming, including both PAUT and TFM.
Because of the large amount of FMC data that must be processed to produce a TFM image, the total focusing method may imply lower productivity than PAUT with the same aperture.
Although the TFM image is highly focused on the entire region of interest, it remains affected by the same acoustic limitations that hamper PAUT. Amplitude fluctuations and distortions are observed in both PAUT and the TFM, but the results for a set of identical scatterers in an inspected part are more consistent for the total focusing method.
A shorter inspection time will always be a priority in NDT. Whereas PAUT gives us real-time feedback, TFM acquisition is time-consuming. Most PAUT machines lack multiple channels for a faster TFM acquisition.
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