[charlie]

I cannot speak in the name of the standardisation organisation, but as a manufacturer we can certainly highlight some new variables that might have an impact over your inspection result.
First, as you probably have noticed, the FMC data, could be acquired using Phased-array equipment. Because of that similarity, a lot of variable having an influence for the PA technique would have an impact over your FMC/TFM inspection, such as velocity, phased-array system, probe parameter, wedge parameter, Encoding device, scan parameter …. Those PA parameters would probably be a mandatory variable as well for the FMC/TFM inspection.
The new parameter

-The TFM algorithm would calculated the TFM image based on the selected mode velocity. Hence the propagation mode selection is a major parameter for this new technique. Some modes are known to be more sensitive for specific flaw orientation. Hence, if you may be able to qualify one weld configuration using one mode only, you may need two or more mode to qualify complex weld geometry. Validated your inspection setup on mock up is the best practice here in case of doubt. Typically ; TT mode are more sensitive for direct flaw, TTT mode are better for vertical flaw, and the TT-TT mode are more sensitive for rebound flaw.

-Also, an insufficient image resolution, may induce a lost in amplitude fidelity. This is a similar phenomena as the conversion of an analogue signal into a digitalise signal (image resolution≈ acquisition frequency). If your inspection procedure is amplitude based, you must be carful with this parameter. To stay in within 2dB amplitude tolerance Sonatest would recommend a minimal resolution of λ/5. The amplitude tolerance would increase as this ratio decrease.

-The Zone of interest is the physical area inside your part where you want to calculate the TFM image, this parameter has a huge impact in case of mistake.
– The FMC signal characteristic requirement, shall be in RF rectification mode, the A scan shall have an sufficient acquisition frequency and the ADC resolution should be high enough (12 bit or higher). Any new filter or signal processing should be validated as well and would impact your TFM image.
-Any image smoothing, or enhancement might have an impact over your inspection and should be validated if changed.
I think those are the main parameter, but might not be exhaustive neither, don’t heisted to contact me if you have interogatation on a specific point
Also, If you want a learn more about the Sonatest solution I invite you on our YouTube channel were a a webinar on our FMC/TFM solution would be release soon.
https://www.youtube.com/user/TheSonatest
Hope I could helps