Phased Array Ultrasonic Testing with TFM/FMC
The nondestructive testing (NDT) industry is experiencing an important technological advancement, as total focusing method (TFM) / Full Matrix Capture. The TFM approach represents a significant step forward for phased array ultrasonic testing (PAUT) technology. However, some PAUT practitioners may still be confused about TFM and its relation to full matrix capture (FMC), as well as the differences between conventional PAUT and TFM/FMC processing.
What is the Total Focusing Method Algorithm?
The total focusing method algorithm can provide greater clarity and precision compared to standard phased array ultrasonic testing. To understand how, it’s important to grasp what information is lost during standard phased array.
Standard phased array technology employs a “sector scan” method of inspection. First, the software decides on a focal law—the calculation used to interpret scan results. Then, the array pulses, receives a signal back, and digitizes the signal. It uses the delay law to sum the signals from each receiver together, discarding raw data.
Then, the instrument changes beam angles, calculates a new focal law, and pulses again to repeat this process. The results of each sector scan, are summarized to create a Sectorial, Linear, or Compound scan image.
In contrast, the total focusing method algorithm does not summarize. Data from each transmitter/receiver in the array is separately digitized and saved, a technique known as Full Matrix Capture (FMC). From this data, the software calculates a focal law for every pixel in the image. Analyzing FMC data using TFM focal laws provides a different view from conventional phased array.
TFM does not replace standard phased array. It is, however, a powerful tool to augment PAUT, improving image resolution and the ability to characterize smaller flaws.
1st Step: Data Collection with Full Matrix Capture (FMC)
2nd Step: Reconstruction: Total Focusing Method (TFM)
Main Advantages of TFM
Uses for TFM in Phased Array Ultrasonic Testing
Utilizing the total focusing method can help technicians identify small defects or flaws in challenging inspections. While standard PAUT remains the method of code and regulation, TFM can still help industries improve safety and maintenance results. Here are some examples of useful applications, based on case studies, for TFM:
|Hydrogen Induced Cracking||Wet H2S refinery environments||This type of cracking can occur at low temperatures. Standard PAUT may not show stepwise internal cracks between hydrogen blisters.|
|High Temperature Hydrogen Attack||Refineries, Petrochemical, Chemical||Voids in steel < 0.1mm in the early stages of HTHA are difficult to detect without the advanced capabilities of TFM.|
|Dissimilar Metal Welds||Nuclear, Oil and Gas||Complex geometries, multiple acoustic interfaces, and austenitic structure propagation issues create difficulty for standard PAUT.|
Identifying issues early on using TFM allows managers to plan repairs or replacements well in advance, ensuring the most efficient allocation of maintenance resources. Swapping unplanned downtime for scheduled maintenance keeps operations moving, and detecting failure points early protects workers as well as the bottom line.
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