In ultrasonic testing, a transducer sends a pulsed sound wave at ultrasonic frequency into the material being tested. The reflected sound wave is detected by another transducer and the diagnostic equipment, to which the transducers is attached, is able to indicate the presence of defects in the piece being tested.

Ultrasonic waves are known to have excellent penetration into most materials, and so are capable of detecting deep flaws. Also, the high sensitivity associated with the technique allows extremely small flaws to be detected. Further benefits of ultrasonic inspection include:

• Only one surface need to be accessible
• Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces
• Some capability of estimating the size, orientation, shape and nature of defects
• Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity
• Capable of portable or highly automated operation