Ultrasonic Testing (UT) uses high frequency sound energy to conduct inspections and take measurements. UT inspection can be used in various ways, some of them are: flaw detection/evaluation, dimensional measurements, finding out characteristics of certain materials, thickness gauging and many more. Below is a basic diagram to illustrate how UT inspection works.
Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of ultrasonic inspection are:
- Able to detect both surface and sub-surface discontinuities.
- The depth of penetration for flaw detection & measurement is far greater than that of any other NDT methods.
- Usually only access to one side of the test piece is required.
- UT is highly accurate in determining the flaw / reflector position and able determine size and shape.
- Minimal preparation is required for test piece.
- Specialized electronic equipment provides instant results.
- Highly detailed images can be produced with automated UT systems, i.e. Phased Array & C-Scan.
- Other uses, commonly used in refineries and plants include Thickness Gauging (see picture below).
As with other NDT methods, Ultrasonic inspection has its limitations, these include:
- Surface must be accessible in order to conduct UT inspection.
- High operator skill & extensive training is required.
- It usually requires a coupling medium (i.e. Water, Ultrasonic Gel, Heat Gel).
- Materials are hard to inspect when they; have a rough surface, are irregular in shape, are very small and exceptionally thin.
- Certain materials i.e. Iron & coarse grained materials, are difficult to inspect due to high noise, sound scatter and low penetration.
- Defects parallel to the sound beam may go undetected.
- Reference standards are required for both calibration of equipment and characteristics of flaws.