Which type of couplant is most commonly used in Ultrasonic Testing?

In Ultrasonic Testing (UT), the most commonly used couplant is gel. Gel serves as an effective medium to facilitate the transmission of ultrasonic waves between the transducer and the test material. It helps to eliminate air gaps that can interfere with sound wave propagation, ensuring that the ultrasonic signals accurately penetrate into the material being examined.

Gels are specifically formulated to provide a proper viscosity and adherence, allowing them to remain in place during the testing process. This property is crucial since a stable layer of couplant ensures consistent and reliable readings which are vital in evaluating material integrity. Additionally, gel couplants typically have lower evaporation rates compared to other liquids, which helps maintain performance during prolonged testing sessions.

While grease and water can also be used as couplants in certain applications, they do not provide the same level of performance or convenience that gel does in most ultrasonic testing situations. Air is not practical as a couplant since it acts as a barrier that prevents effective transmission of ultrasonic waves, leading to poor or no signal return.