instrument, creating A-scan information in real time and
generating images that are essentially stacked A-scans,
as opposed to FMC/TFM, which is non-beam-forming.
F-451.1 Typical Workflow Process. Figures
F-451.1-1 through F-451.1-4 illustrate the typical workflow
processes mentioned in F-450 and illustrate that
for PAUT the following is true:
a The delay law calculation is determined by the type
of image reconstruction sector scan, linear scan, etc. and
other parameters such as travel time to the focus point.
b The data acquisition method can be determined by
the type of focusing [typically the case of dynamic depth
focusing DDF, zone focusing, linear scan, or sectorial
c The active focusing necessitates that the focal laws
be generated prior to acquisition.
F-451.2 Advantages of TFM Synthetic Focusing.
The following are some of the advantages of TFM:
a Only one FMC data acquisition is enough to generate
the various images, even when the equipment processed
a different mode during acquisition or the FMC
data was stored such that the TFM processing software
could reconstruct several modes. Instead of only for that
mode, it is possible to apply various TFM processes to
stored FMC as well.
b An accurate model of the component can be generated
with FMC data, which improves the resolution, and is
a function of the array and wedge definition and of the position
of the grid. In addition, the ability to resolve component
and weld geometry in the reconstructed image has
advantages e.g., verification of equipment setup and less
c The settings e.g., focal law calculations can be
completely disassociated from the acquisition. In the case
of elementary FMC/TFM, the only relations are the array
pitch, velocities, and, when the TFM process is not adaptive,
the relative geometry of the search unit with the part.
d Complex or high-performance TFM methods offer
greater flexibility to correct for the lack of knowledge of
the inspected part and its characteristics, enhance the resolution,
improve profiling of the indication, reduce material
structural noise, etc.
TFM is the result of the computation from data that was
acquired independently. It brings possibilities such as
using different processing, with the same FMC data, at
the same time or in post processing, using different algorithm
s. This may be advantageous for a particular examination
F-462 GENERAL CALIBRATION REQUIREMENTS
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F-462.1 Amplitude Fidelity. In simple terms, amplitude
fidelity is the digital preservation of the signal amplitude
information. The difference is a variation in
sensitivity. The issue can either be that the amplitude varies
too much because of the range of the grid size or by
having too coarse a grid resolution regarding the lateral
resolution of the system. There are several factors that influence
the outcome, and an inadequate setup for a given
component can lead to poor examination results.
Some of the parameters that can affect amplitude fidelity
are physical properties, such as component material,
search unit characteristics, wedge definition, and the position
of the grid relative to them. Other parameters that
may affect amplitude fidelity are FMC instrument settings
e.g., the sampling frequency, range, and dynamic setting
and settings and particularities of the TFM processes used
by the equipment. The definition of the grid is essential
for this check and therefore for the examination.
There are many ways to check or calculate amplitude
fidelity for a given setup. The following is one example
using a side-drilled hole SDH in proximity to the surface,
yet past the dead zone, with an additional SDH placed
0.2 in. 5 mm from the back wall, by observing the amplitude
response while moving the search unit to cover the
whole grid from each extremity of the search unit across
the SDHs. Scanning across the SDHs should be done with
an encoder employing a micro-adjustment, such as
0.004 in. 0.1 mm. If the SDHs are separated by 0.2 in.
5 mm or less, due to thickness, then one hole is adequate.
When using two holes, it is necessary to space them
enough laterally to avoid the response from one influencing
This example consists of moving the search unit along
the test piece laterally such that the grid to be used during
the examinations scans the SDHs and displays each
along the lateral axis. The amplitude of the signal can be
observed and measured for each position of the grid relative
to the SDHs.
FMC/TFM Generic Workflow
ARTICLE 4 ASME BPVC.V-2023