For many applications this requirement is easily met. The only exception I can think of is tube testing where a 100 mm diameter tube would exceed this speed on the outside at 700 rpm. Although this is fast some systems can go that fast. A similar procedure can be used at other frequencies and times of flight. If you are measuring the wall thickness then both of these effects also apply but the sampling issue is governed by the rate at which the part thickness can vary.
Examples abound of under thickness tubing parts escaping detection because of insufficient sampling.
This is more of a problem on wall thickness units because they often do not use one pulse to make a measurement or take a relatively long time to make a measurement. This means a 10 mm diameter tube spun at 3,000 rpm will only be sampled 4 times per revolution. It is unlikely that the 4 will reliably adequate define the wall thickness. Every time the transducer is pulsed the system takes a sample of the moving part. We want this interval either smaller than the smallest flaw or smaller than the beam diameter.