The Equipment track of our GWT training series opens with the topic I believe matters most: coupling.
The success or failure of a field inspection is decided by coupling condition. This isn't a minor detail — it's the foundation everything else in GWT depends on.
In ordinary UT, it would be nonsense to report a finding without showing the signal that confirms coupling quality. Yet in GWT, detailed coupling-quality images have essentially never appeared in field reports — across the industry, with the MsS system as the exception — for more than 20 years.
A GWT detailed data plot of a 3- to 5-ft section is similar to a UT A-scan. Instead, GWT has been reported with a one-page plot and DAC curves for 200 ft of coverage. That's not a GWT report — it's Guided Wave Showing (GWS), where a number is simply asserted, not proven.
The verbal proof of GWS is saying "the software did," when asked how the inspection range and attenuation were decided. Documentary evidence that a GWT inspection was not properly performed by a Level 2 inspector includes not reporting an indication or weld signal's % reflection value, and not including a detailed UT image for that section.
Who can believe a GWT report that does not include one detailed UT plot? Who can find any defect without looking at the detailed UT signal? GWT has real limitations, just like every other NDT method — geometric features, high-viscosity content, thick coatings, generalized corrosion, surface roughness. All of these affect coupling and signal quality. And yet, inspection after inspection gets reported as simply "successful," with none of that underlying detail shown.