Here is a recent video from Intero. I spoke to them at the RefComm Conference earlier this month. My understanding is that they can use sound waves to inspect your pipes in the refinery. Sound is emitted from the pig and it bounces off the pipe wall. Depending on the deformities in the pipe, the time it takes the sound to return to the pig varies.
I have spoken to companies in the past that use magnetic flux to find deformities in pipelines; but this is the first time I have investigated systems that use sound. Please enjoy the video.