A review of the purpose and benefits of ultrasonic testing.

Ultrasonic method or testing is a non-destructive test that sends soundwaves through a material. Most Ultrasonic applications use short pulse waves ranging from 0.1 to 15 MHz frequency, but in rare cases frequencies of up to 50MHz can be used.

Ultrasonic inspection can occur in two different methods; contact or immersion ultrasonic testing.

  • Contact inspection is often used where radiographic testing is not possible because the test specimen can only be accessed from one side, or it can’t be moved. It allows for the inspection of objects that are large, irregular shaped and immobile because you only need to access one side.
  • Immersion inspection, on the other hand, is a laboratory-type of testing used to detect smaller defects like cracks and porosity. Submerging an object in water allows for better sound travel from the transducer hence providing a more accurate report of sub-surface flaws. Immersion ultrasonic method is more superior because it applies to a broad range of materials and thickness.

What is the Purpose of Ultrasonic Testing?

The most common application for ultrasonic testing is to detect cracks, fractures, moving components and defects in objects. It is also used to characterize a material or determine its thickness, for instance, measuring the thickness of a pipe or assessing its corrosion. In other words, UT is used to test the integrity of a component, including testing for welds to see if there are any discontinuities.

The method is ideally used to inspect dense, crystalline structures such as metal and alloys. However, plastics, ceramic, concrete and composites can also be examined using UT, though with reduced resolution.

Regular ultrasonic inspection can pick up small defects and corrosion thus preventing a failure of a particular part or the entire asset. It is used in many industries including automotive, construction, aerospace, medical and manufacturing.

Unlike other non-destructive methods, ultrasonic testing produces images that are more clearly defined and indicate characteristics that are deeper than the surface level. Other advantages of Ultrasonic testing include;

  • Higher penetration power for deeper flaw detection
  • Heightened sensitivity to pick up tiny flaws
  • It can test an object where only one side is accessible
  • Greater accuracy when testing internal flaws and object thickness compared to other NDT methods
  • No-hazardous to nearby personnel
  • Highly automated and portable
  • It’s able to estimate the size, shape and nature of defects in a test object

How do you use Ultrasonic Testing?

A typical UT inspection involves a transducer, pulser/receiver, and a display device. An ultrasound transducer connected to the diagnostic machine is passed over the test object. You have to separate the item and the transducer with a couplant which can be oil or water.

The high-frequency sound waves penetrate through the object until they hit a boundary with another medium, even if its air. At this point, the sound waves will reflect back to the source. You can therefore measure the thickness of the test object or find evidence of flaws and cracks by analysing that reflection.

Because of the scientific knowledge required in ultrasonic testing, it must be done by trained and experienced technicians who will do and interpret the data. They will also calibrate the testing equipment using common standards like IIW block   or other calibration blocks to ensure its taking data correctly and consistently.