Couplant Layer
Couplant is a liquid or pasty medium between the probe and the material surface that bridges the acoustic impedance and transmits sound energy with low loss.
Physicochemical mechanism of action
The couplant forms a thin layer between the probe and the material surface. It reduces acoustic impedance by minimizing the direct contact area between these two elements, allowing sound energy to be transmitted more efficiently.
Metallurgical relevance & welding risks
Proper couplant is critical for accurate ultrasonic testing (UT). A couplant that is too thin or missing can impair sound transmission, leading to inaccurate results. A too-thick couplant can absorb sound energy and distort the signal, also causing false diagnoses.
Workshop practice & action instructions
For successful UT, the couplant layer must be thin and uniform. The recommended thickness is usually between 0.1 mm and 0.3 mm. Always use a high-quality couplant and make sure it is fully applied to the material surface. If signal issues occur, first check the couplant's thickness and material.