Ultrasonic Couplant
Ultrasonic couplants are liquids or gels that bridge the air gap between the probe and the component. They improve sound entry because they transmit ultrasound better than air.
Physical-Chemical Mechanism
Ultrasonic couplants are substances with high density and low elasticity. They minimize reflection of ultrasound at the surface by having a sound velocity nearly matching that of the metal. This leads to more effective transmission of sound from the probe to the part.
Metallurgical Relevance & Welding Risks
Without a suitable couplant, ultrasound is strongly reflected at the air-part interface, making detection of flaws or cracks difficult. Incorrect or missing couplants can lead to inaccurate results and compromise the test outcome.
Shop Practice & Instructions
Choose a couplant with high compatibility with the metal. For steel, water or a special ultrasonic coupling fluid is suitable. Apply the fluid smoothly to the part surface and ensure it contains no air bubbles. A thin layer is sufficient to bridge the air gap.