If the cleanliness requirements are high, use ultrasonic cleaning:
Ultrasonic cleaning principle: when ultrasonic wave propagates in liquid, the violent change of sound pressure leads to strong air phenomenon in liquid, producing millions of tiny cavitation bubbles per second. These bubbles are produced rapidly and in large quantities under the action of sound pressure, will not continue to explode violently, and produce strong impact force and negative pressure suction, which is enough to quickly peel off stubborn dirt.
If the seamless steel pipe is long and has its own water tank, you can buy an ultrasonic vibrating plate and put it into the water for ultrasonic cleaning. If the time is not long, the ultrasonic vibrating rod can be inserted into the pipe for cleaning, and then the dirt stripped by ultrasonic can be washed off with tap water.