Ultrasonic Testing (UT)
Ultrasonic inspection uses sound waves of short wavelength and high frequency to detect flaws or measure material thickness. It is used on aircraft, the power stations generating plant, or welds e.g. in pressure vessels, ships hulls, paper mills.
Sophisticated instruments emitting pulsed beams of high frequency ultrasound are used. The ultrasound is usually transmitted via a hand-held transducer which is placed on the specimen. Any sound from that pulse that returns to the transducer (like an echo) is shown on a screen which gives the amplitude of the pulse and the time taken to return to the transducer.
The test instrument analyzes the ultrasonic signals received using either a pulse-echo or through-transmission method. In the pulse-echo mode, the transmitting transducer also serves as the UT receiver and analyzes the reflected signal with respect to amplitude and time. In the through-transmission mode, the UT signal is received by a separate transducer which analyzes the amplitude loss of signal. In general, defects anywhere through the specimen thickness reflect the sound back to the transducer. Flaw size, distance and reflectivity are measured and can be interpreted to indicate material defects e.g. cracks or inclusions, as well as dimensional changes e.g. thickness.
Because of its complexity, considerable UT user training and skill is required.