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Eddy Current Testing Theory Flashcards

7 cards from real NDT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Eddy Current Testing Theory flashcards as text

  1. Which of the following materials has the HIGHEST electrical conductivity, making eddy current testing most effective at low frequencies?

    Answer: Copper

    Copper has electrical conductivity of approximately 58 MS/m, far higher than titanium, stainless steel, or carbon steel, allowing eddy currents to flow very freely.

  2. What is 'phase analysis' used for in eddy current testing?

    Answer: Distinguishing between different types of discontinuities and their depth

    Phase analysis uses the phase angle of the eddy current signal to discriminate between defect types (surface vs. subsurface) and estimate their depth.

  3. An eddy current technician notices the signal drifts continuously during scanning of a large aluminum plate. The MOST likely cause is:

    Answer: Thermal drift changing probe impedance as temperature varies

    Thermal drift occurs when probe or material temperature changes during scanning, causing a gradual impedance shift unrelated to defects.

  4. In the context of eddy current testing, what does 'fill factor' describe for encircling coil probes?

    Answer: The ratio of the test piece cross-sectional area to the coil's inside area

    Fill factor (η) is the ratio of the test piece's cross-sectional area to the coil's inner cross-sectional area, and a higher fill factor improves coupling and sensitivity.

  5. When testing nonconductive coatings over a conductive substrate, the eddy current technique can measure coating thickness because:

    Answer: Coating thickness changes the effective lift-off distance from the conductor

    A nonconductive coating acts as a spacer, increasing the effective lift-off between the probe and the conductive base material, which is directly related to coating thickness.

  6. What is the characteristic impedance plane trace for a surface-breaking crack as probe scan speed increases?

    Answer: The signal may become distorted due to filtering effects at high speeds

    At high scan speeds, the instrument's filter bandwidth may not keep up with rapid signal changes, causing waveform distortion and potentially missing narrow cracks.

  7. Which eddy current testing application most commonly uses a 'horseshoe' or 'U-shaped' probe?

    Answer: Fastener site inspection through multiple layers

    U-shaped (transmission) probes are used for multi-layer fastener site inspection, where the driver coil is on one side and the pickup coil on the other side of the structure.