ultrasonic inspection

A nondestructive test method that employs high-frequency mechanical vibration energy to detect and locate structural discontinuities or differences and to measure the thickness of a variety of materials. Radiation frequency is of the order of 0.1 to 25 MHz. The beam travels unimpeded through large parts, may be angled for testing sheet stocks, and can impact materials immersed in liquids. Access is required to only one side of the material being tested. This NDT (nondestructive testing) method can detect microstructural alterations, such as microcracks, foreign particles, precipitates, grain boundaries, interphase boundaries, and dislocation defects. For corrosion detection, pulse-echo and resonance methods are used. The frequency of the vibration in this case is usually from about 0.5 to 25 MHz. The vibrations travel through the material and bounce back. There are three pips on the CRT (cathode-ray tube). One represents the front and the other the back of the material. If there is inter-granular corrosion, then it will appear as the third pip, as shown in the illustration.

Cathode ray tube indicator corrosion.

Some ultrosonic non-destructive testing methods.