What is the purpose of couplant in Ultrasonic Testing?

The purpose of couplant in Ultrasonic Testing is to eliminate air gaps between the transducer and the test surface. In ultrasonic inspection, sound waves are transmitted from the transducer into the test material. For efficient transmission of these sound waves, a medium that can effectively transfer the energy from the transducer to the test material is required. Air acts as a barrier, greatly reducing the intensity of ultrasonic waves because sound propagates poorly through air due to its low density compared to solids and liquids.

Using couplant—such as oil, water, or gel—fills the gap between the transducer and the material being tested. This coupling medium has acoustic properties that allow sound waves to enter the test material efficiently, ensuring that the ultrasonic signals can travel without significant loss of energy. This enhances the quality of the testing and allows for accurate detection of flaws or defects within the material.

The other options, while relating to ultrasonic testing, do not accurately capture the primary function of couplant. Strengthening the signal or adjusting the velocity of sound are not the fundamental roles of couplant, as the purpose is solely to provide a continuous path for sound waves by removing any separation between the two media.