Non-Destructive Testing (NDT) Methods Flashcards

What is the primary principle behind eddy current testing?

Answer: Alternating magnetic fields induce eddy currents in conductive materials, and changes in those currents indicate defects

Eddy current testing works by inducing eddy currents in electrically conductive materials via alternating magnetic fields; discontinuities or material variations alter the eddy current flow, changing the coil impedance that is measured.

What is a couplant used for in contact ultrasonic testing?

Answer: To eliminate the air gap between the transducer and the test surface, enabling sound transmission

A couplant (such as water, oil, or gel) fills the air gap between the transducer and test surface because ultrasonic sound waves cannot effectively transmit through air.

On an A-scan ultrasonic display, what do the peaks (echoes) represent?

Answer: Reflections of sound energy from surfaces, boundaries, or discontinuities within the material

On an A-scan display, peaks represent reflected ultrasonic echoes from surfaces or internal discontinuities; the horizontal axis shows time (depth) and the vertical axis shows signal amplitude.

Which eddy current probe orientation is most effective for detecting cracks perpendicular to the surface on a flat plate?

Answer: Surface (pancake) probe

A surface (pancake) probe placed flat against the test surface is most effective for detecting surface cracks in flat materials because its coil orientation maximizes sensitivity to surface discontinuities.

What effect does increasing the frequency of an ultrasonic transducer have on inspection capability?

Answer: Increases sensitivity to small defects but reduces penetration depth

Higher ultrasonic frequencies produce shorter wavelengths, improving resolution and sensitivity to small defects, but are attenuated more rapidly, reducing penetration depth in the material.

What type of material condition can eddy current testing detect that magnetic particle inspection cannot?

Answer: Surface cracks in non-ferromagnetic alloys such as aluminum and titanium

Eddy current testing works on all electrically conductive materials, including non-ferromagnetic alloys like aluminum and titanium, whereas magnetic particle inspection is limited to ferromagnetic materials.

In ultrasonic testing, what is 'back-wall echo loss' an indication of?

Answer: A large internal discontinuity or severe attenuation blocking the return of the back-wall reflection

Loss of the back-wall echo indicates that a large internal flaw or severe attenuation is preventing the ultrasonic pulse from reaching and reflecting off the far wall of the test piece.