What is the primary purpose of using a couplant in ultrasonic testing?

The primary purpose of using a couplant in ultrasonic testing is to improve sound transmission. In ultrasonics, sound waves are generated by a transducer and need to travel through different materials to detect flaws or measure thickness. However, sound waves cannot travel efficiently through air, as there is a significant impedance mismatch between air and solid materials.

The couplant, typically a gel or liquid, is applied to the surface of the test material to eliminate air gaps between the transducer and the material. By doing so, the couplant allows for better transmission of the ultrasonic waves into the material being tested, ensuring that the waves can pass through more effectively. This improved sound transmission is crucial for obtaining accurate and reliable test results, as it allows for adequate propagation of sound waves, leading to clearer signals and enhanced detection of any flaws.