Inspection Concepts & Techniques
What is the purpose of the couplant used during ultrasonic inspection?
Answer
It excludes air between transducer and part so sound can enter the material
Ultrasonic energy does not transmit efficiently across an air gap, so a couplant (such as oil, gel, or water) is applied to exclude air between the transducer and the test surface, allowing sound to pass into the part. Inducing eddy currents describes eddy current inspection, and cooling the transducer is not the couplant's function.
Source: FAA-H-8083-30B, Ch. 10 (Inspection Concepts and Techniques), 'Ultrasonic Inspection'.
Not the answer
- It cools the transducer to keep it from overheating during the course of the test
- It induces electrical eddy currents in the surface layer of the part being tested
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