Ultrasonic Testing

Ultrasonic non-destructive testing (UT) is commonly used for flaw detection in materials.

Ultrasound uses the transmission of high-frequency sound waves to detect a discontinuity or to locate changes in material properties. A common example is ultrasonic thickness measurement; for example, to monitor pipe corrosion. Considerable information may be gathered during ultrasonic testing such as the presence of discontinuities, material or coating thickness.

In general, ultrasonic testing is based on the capture and quantification of either reflected waves (pulse-echo) or transmitted waves (through-transmission). Each of the two types is used in certain applications, but generally, pulse echo systems are more useful since they require one-sided access to the object being inspected. Normal/Angle Beam and Contact techniques are used.

Some of the most common Ultrasonic applications are:
  • Flaw detection (cracks, inclusions, porosity, delaminations, etc.)
  • Erosion/Corrosion thickness gauging
  • Assessment of bond integrity.
Advantages of ultrasonic testing:
  • High penetrating power, which allows the detection of flaws deep in the part.
  • High sensitivity, permitting the detection of extremely small flaws.
  • Only one surface need be accessible.
  • Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.
  • Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.
  • Manual operation requires careful attention by experienced technicians.
  • Extensive technical knowledge is required for the development of inspection procedures.
  • Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
  • Surface must be prepared by cleaning and removing loose scale, paint, etc., although paint that is properly bonded to a surface need not be removed.