AUT works by using a scanner which is held on to the equipment with magnetic wheels, emitting ultrasonic waves that propagate through the vessel. These waves then travel through the material until they encounter a surface; this causes some of the energy to be reflected. Once acquired, the amount of reflected energy can then be measured and, from this, the thickness of the component and the size of any flaws can be detected. Compared to other inspection techniques, AUT has a high degree of repeatability and multiple scans can be taken over time to track the progress of corrosion. On the other hand, it has similar limitations as well. The preparations that are required to use this method are extensive and the process requires a great deal of interaction between the operating personnel and AUT inspectors, especially in high temperature examination environments, which can make it more difficult in some situations.