Ultrasonic nondestructive testing, also known as ultrasonic NDT or simply UT, is a method of characterizing the thickness or internal structure of a test piece through the use of high frequency sound waves.The frequencies, or pitch, used for ultrasonic testing are many times higher than the limit of human hearing, most commonly in the range from 500 KHz to 20 MHz.
Ultrasonic testing is completely nondestructive. The test piece does not have to be cut, sectioned, or exposed to damaging chemicals. Access to only one side is required, unlike measurement with mechanical thickness tools like calipers and micrometers. There are no potential health hazards associated with ultrasonic testing, unlike radiography. When a test has been properly set up, results are highly repeatable and reliable.