What type of ultrasonic examination uses wheel-type search units that eliminate the use of a tank?

Immersion testing typically requires the use of a tank filled with a coupling medium, such as water, to facilitate the transmission of ultrasonic waves. However, certain advancements in ultrasonic examination techniques allow for the use of wheel-type search units that can operate without the need for a full immersion tank.

This method is often associated with methods like contact testing where the transducer is placed directly on the surface of the material, utilizing a coupling medium, but the inclusion of wheel-type search units indicates a specialized approach that can eliminate the tank typically required in immersion testing. These wheel-type units allow for scanning of surfaces in a more mobile and flexible manner, thus simplifying the examination process.

Through-transmission testing and surface wave testing refer to different methodologies involving sound waves traveling through or along a medium, which do not involve wheel-type search units as defined in this context. Consequently, the answer highlights an innovative technique within ultrasonic testing that enhances practicality and efficiency in inspections.