Zinc thickness on galvanized steel conduit

Is there any measuring instrument that can measure zinc thickness on steel conduit as an in-line operation rather than manually one piece at a time?

My company PVC coats conduit and zinc thickness effects the adhesion. We need to be able to check each piece of pipe at the front of our operation and can only find measuring instruments for sheet not pipe steel.

I believe that portable XRF could do this job. However, it would probably need to be an "at-line" analysis involving a human being rather than "on-line" and totally automated. Also, you would want to make your initial thickness calibration on similar tubing styles of pieces.

Another alternative would be the eddy current gadgets. But again it would involve a human and I would want to try it out on curved pieces pretty thoroughly if I were you.