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Why does use the ultrasound for non-destructive testing?
1. Why do we use the ultrasound for non-destructive testing?
The principle of the ultrasonic inspection method is based on the fact that the hard materials are good conductors of sound waves. Whereby, the waves are reflected not only from boundary surfaces, but also they are reflected from internal flaws (cracks, various inclusions, etc.). The effect of the interaction of sound waves with the material is enhanced with decreasing the length of the waves (and, consequently, increasing the frequency of oscillation).
λ = c / f , where
c – sound speed [km / s];
f – frequency [MHz];
λ – wave length [mm].
So that, many tasks of testing can be solved with more economical and more safety ultrasonic method, and in some specific problems as before, use the X-rays devices. In cases where there are the highest safety requirements (nuclear power stations, aerospace industry) are used both methods.There are two the most commonly used method of testing the internal structure of the materials: radiography and ultrasonic. These researches partially overlap and complement each other.This means that the ultrasonic waves can be used the most effectively in the frequency range from 0.5 MHz to 25 MHz. Using ultrasonic waves with the lower frequency, will reduce the effect of the interaction of waves with internal defects, and the detection of defects in metal structures becomes problematic (long waves encircle the defects).
2. Tasks of ultrasonic testing
If you restrict the using of the ultrasonic method only for detecting the internal flaws of the material, the classification of tasks of the operator will be the following:
1) Detection of reflectors;
2) Determination of their location;
3) Evaluation of the size of the reflectors
4) Determination of the properties of the reflectors (type, orientation, etc.).
Instead of using the word “reflector”, specialists often use the term “discontinuity”. This term is defined as “incorrectness” in the structure of a control object, which is presumably a defect”. In fact, only after the determination of position, analysis and evaluation, user can determine whether there is a lack, which It affects the suitability of the tested object for use object. Until there will be the confidence that the detected reflector is a “defect”, the term “discontinuity”is always used. For these tasks, we are supplying Ultrasonic Flaw Detector NOVOTEST UD2301 and Ultrasonic Flaw Detector NOVOTEST UD-1.