Re: UT scanning Using a proper transducer and instrument setup, you should be able to measure the wall thickness of any stainless steel pipe that you're likely to encounter. Using a 20 MHz delay line transducer you could measure as thin as 0.25 mm, and using a 500 KHz contact transducer you could measure as high as 100 mm (and much thicker in carbon steel as opposed to stainless). For typical pipe wall thicknesses in the 10 mm to 20 mm range we would usually recommend working at 2.25 MHz.
Note that inexpensive ultrasonic gages designed for corrosion survey will sometimes have problems on stainless steel because of grain scatter noise. Better instruments typically permit gain and blanking adjustments that will allow you to work around that problem.