Ultrasonic Testing

The velocity of ultrasound in any given material is a constant for that material and ultrasonic beams travel in straight lines in homogeneous materials. When ultrasonic waves pass from a given material with a given sound velocity to a second material with different velocity, refraction and a reflection of the sound beam will occur at the boundary between the two materials. The same laws of physics apply to ultrasonic waves as to light waves. Ultrasonic waves are refracted at a boundary between two materials having different acoustic properties so probes may be constructed which can beam sound into a material at (within certain limits) any given angle.

Because sound is reflected at a boundary between two materials having different acoustic properties ultrasound is a useful tool for the detection of weld defects.

Since velocity is a constant for any given material and sound travels in a straight line (with the right equipment) ultrasound can also be used to give accurate positional information about a given reflector.

Careful observation of the echo pattern of a given reflector and its behaviour as the ultrasonic probe is moved together with the positional information obtained above and knowledge of the component history enables the experienced ultrasonic operator to classify the reflector as slag, lack of fusion or a crack.