I didn't see anything in the post about materials, codes, techniques, industry etc. To quote the OP:
"Ihave a customer that just had to do a ton of rework because they were failing UT examinations. If a defect was found that was planar and exceeded 1/64" in dimension (if it's planar, must be in 2 dimensions, right?). Then it was a fail. Can UT Reliably and repeatably find defects of this size?"
My response;
"1/64" is 0.015625.
Don't know what material is being examined, technique deployed, etc, but as a general rule, the smallest detectable flaw is 1/2 of the wavelength.
Wavelength = velocity/frequency.
Can UT reliably and repeatably find flaws that size? That answer is dependent upon many factors, but as a general rule, yes. Are the technicians always capable? no. "
c
Given the lack of pertinent information, the answer stands as a theoretical yes. BTW, a 1/64" flaw in 'any' direction is rounded.
Calculate the wavelength for various materials, then consider the .015625" flaw size. Now lets match up a theoretical:
Lets pick titanium and list the wavelengths for longitudinal @ a velocity of 6100m/s:
1mhz = .24015748"
5mhz = .04803149"
7.5mhz = .032020997"
10mhz = .024015748"
15mhz = .016010498"
It becomes clear that it is definitely detectable. For aerospace applications in thin walled materials, it's not that unusual. Mapping btw isn't that hard or complicated for an automated system such as an automated immersion bed. It can be done manually as well. Remember, the typical 6dB drop method isn't 'the only' method. There are ID OD rolls, Time of flight crack tip diffraction, immersion delta technique, etc etc. Then there is also the assumption of wave form being made. Lamb waves, Raleigh waves, Flexular waves (Antisemmetrical lamb waves), etc etc.
Bottom line, we were not given enough information. When it comes to theory, yes in fact it can be done.
Now if we are talking a typical structural or pipe scans, I'd have to raise the flag.