Performing MUT with same equipment on this sample gave me this result:

https://youtu.be/1HmtLeis-5c

As there was only 1mm remaining wall, HydroForm would not detect the same and it would look like a just signal loss due to poor surface.

To be sure that pitting would be detected and sized with Phased Array, I scanned with Dual Linear Array and this is what it looked like:

https://youtu.be/UIAjdCxB0UM

Final Result:

Has anybody else experienced something similar on the job? We do know limitations in UT / MUT but in many cases clients would ask for corrosion scanning on old pipe or vessel where scanning surface is not perfect and would expect perfect results every time.

Our working environment is not office lab and every now and then when you lose a signal on A scan display, would you think its pitting like this or just lack of couplant or bad surface?