How Does Ultrasonic Non-Destructive Testing Work?

Ultrasonic testing is a pretty common staple of the non-destructive testing sector of the engineering industry. Ultrasonic testing uses high-frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used to detect and evaluate flaws, measure dimensions, characterise materials and more. This testing method is ideal for detecting flaws and defects without damaging the object undergoing testing. Periodic testing can be used to check for corrosion or growth of known flaws and therefore enables components to be switched out before they become too damaged to operate.

Ultrasonic testing works based on the principle of oscillation – an object moving backwards and forwards very fast. This principle is extrapolated by the fact that waves move at different speeds through different objects. As a sound wave is projected through a test object, it is reflected by echo signals at an interface: for instance, the back of the object or an imperfection. Results of an ultrasonic test are displayed as a line graph, with the y-axis representative of the reflection’s intensity and the x-axis representative of distance or time. The gradient therefore gives the depth of the signal through the material. Essentially, imperfections in a material reduce the amount of sound which is received, allowing the location of flaws to become evident.

Ultrasonic non-destructive testing uses a piezoelectric transducer connected to a flaw detector, which, in its most elementary form is a pulser-receiver and oscilloscope display. The transducer passes over the test object during inspection. The test object is usually covered in gel, oil or water to conduct waves more effectively. In pulse echo testing, the same transducer emits and receives the sound wave. Through-transmission testing uses an emitter to send the waves through one surface and a separate receiver to receive the sound waves which reach the opposite side of the test object.

There are two types of ultrasonic NDT. Contact ultrasonic testing is generally used for on-site inspections where portability is key. Contact testing can be used in instances where only one side of a test specimen is reachable or if the test object is too large to transport to a laboratory.

In contrast, immersion ultrasonic testing is laboratory-based technique most-suited to curved components and complex geometries. In this method, the test object is fully submerged in water which acts as a couplant in place of the gels used in contact ultrasound.

Ultrasonic testing is an appropriate inspection method in many industries. It’s typically used to evaluate dense, crystalline structures such as metals. Ceramics, plastics, composites and concrete, however, can also be effectively inspected, but with reduced resolution. Ultrasonic testing is also used in the medical sector.

Ultrasonic testing has several advantages:

  • High penetration power.
  • High sensitivity.
  • High accessibility (can be used when only one side of an object is accessible).
  • Greater accuracy when determining depth of flaws and thickness of parts.
  • Non-hazardous to nearby personnel, equipment or test objects.
  • Highly automated and portable.

Ultrasonic testing also has several limitations:

  • Requires experienced technicians to operate.
  • False positive results sometimes occur.
  • Rough, irregularly-shaped, very small or thin objects are difficult to inspect.
  • Loose scale or paint needs to be removed before testing proceeds.
  • Couplants are required for conventional ultrasonic tests.

Contact NDT Australia

If you are looking for ultrasonic non-destructive testing equipment, check out NDT Australia’s online store. We supply a range of NDT technology, including magnetic particle testing, radiographic and ultrasonic non-destructive testing equipment. We are open for business Monday to Friday, 7:30am to 4:00pm. Contact our friendly sales team on (02) 9524 0558 to ask any questions or to place an order for any of the products listed on our online store.