ULTRASONIC TESTING is a nondestructive testing method of examining materials by introducing ultrasonic waves into, or onto the surface of the part being examined and determining various attributes of the material.

Ultrasound waves are generated by piezo electrical transducers which convert electric oscillations into mechanical vibrations and vice-versa. These waves are made to impinge on the material to be tested. As the wave travels through the material, it may get reflected, refracted, scattered or transmitted depending upon the condition within the material. From a defective location, the waves get either reflected or attenuated. These signals are picked up by the transducer and recorded for display as time pulse-height-pattern on a screen of a cathode ray tube (CRT). Spacing between pulses and height of pulses are interpreted in terms of relative location and size of the flaw in the material.

Ultrasonic waves are classified on the basis of the mode of vibration of the particles of the medium with respect to the direction of propagation of the waves, namely longitudinal, transverse and surface waves

The instruments which display the ultrasonic test information are known as Ultrasonic Flaw Detectors. Three major components of an ultrasonic system, are the transducer that generates ultrasound, the pulser -receiver which acts as communicator between the transducer and display and a screen to display test signals

In industry, ultrasonic frequencies in the range of 0.5 - 25 MHz are common. Various types, sizes and shapes of transducers are available. Three important methods of ultrasonic testing are pulse-echo, transmission and resonance techniques.

APPLICATIONS OF ULTRASONIC TESTING -

The Pulse-echo technique is the most versatile ultrasonic method for non-destructive testing and is the most widely used. Weld testing is the largest application of ultrasonic testing. Pipes of virtually all sizes can be inspected ultrasonically for internal & surface defects. Another very important application of ultrasonic testing is the finding of dangerous incipient defects in components in service, e.g. fatigue cracks and effects of corrosion.

ADVANTAGES -

1. Testing can be carried out from only one accessible surface.

2. At a time, very large section thickness can be tested.

3. Results are immediate. Hence on the spot decision can be made.

4. Cost involved is cheaper as compared with other volumetric test methods.

5. P rovides quantitative information regarding thickness of the component, depth of an indicated discontinuity, size of the discontinuity etc.

LIMITATIONS -

1. Maximum penetration in fine-grained steel and aluminum is in the range of several meters. But in coarser structures, which scatter the ultrasound waves very strongly, like castings, especially cast iron and stainless steel, it is drastically less.