Ultrasound testing is a non-destructive method in which beams of high-frequency sound waves are introduced into a test object to measure wall thickness or to detect flaws in the material. The audible frequency range for the human ear is between 20 Hz and 20 kHz: sound waves with frequencies above 20 kHz are called ultrasound.
In ultrasound wall thickness measurement (WM), an ultrasound transducer is used to generate an ultrasonic wave in a sensor probe that is then propagated through a liquid coupling medium and the surface of the coupled test piece. The couplant is required to ensure no air gap between the probe and the material to be tested, given’s air’s relatively poor sound conducting characteristics. The transducer records the reflections (echoes) caused by both the adjacent and the remote surfaces of the material to be tested – in case of pipes, their internal and external surfaces:
The differences in the arrival times of these reflections are directly related to the distance between the transducer and the surfaces of the test piece. Thus, on the basis of the reflections of the ultrasonic wave, the thickness of the material can be assessed. In Inline Inspection, a distinction can even be made between metal loss on the internal and external surfaces of a pipe.
This effective and reliable technology has a wide range of applications in many industrial sectors. A typical application is the inline inspection of pipelines, where ultrasound WM provides information about wall thickness and the presence/location of discontinuities or flaws (corrosion).