CWI Nondestructive Examination Methods 5 — Questions and Answers
Question 1: What is the purpose of a couplant in contact ultrasonic testing?
- To lubricate the transducer for easy movement
- To exclude air between the transducer and test surface and improve sound transmission (Correct answer)
- To increase the velocity of sound in the material
- To magnetize the test surface
Correct answer: To exclude air between the transducer and test surface and improve sound transmission
Couplant fills the air gap between the transducer and test surface, allowing efficient transmission of ultrasonic energy into the material.
Question 2: A radiograph shows a dark circular spot with a lighter center. This indication is most consistent with:
- Slag inclusion
- Tungsten inclusion (Correct answer)
- Porosity
- Lack of fusion
Correct answer: Tungsten inclusion
A tungsten inclusion appears as a lighter (whiter) area due to its high density, while the surrounding area may be darker; a dark spot with a lighter center is characteristic of a tungsten inclusion.
Question 3: When performing PT on a part in direct sunlight, which type of penetrant is most appropriate?
- Fluorescent penetrant
- Visible dye (color contrast) penetrant (Correct answer)
- Solvent-removable fluorescent penetrant
- Water-washable fluorescent penetrant
Correct answer: Visible dye (color contrast) penetrant
Visible dye (color contrast) penetrant does not require UV light and can be used in ambient lighting conditions including sunlight.
Question 4: In magnetic particle testing, which magnetization technique is best for detecting discontinuities oriented parallel to the length of a cylindrical bar?
- Longitudinal magnetization (coil method)
- Circular magnetization (head shot) (Correct answer)
- Yoke method
- Prod method
Correct answer: Circular magnetization (head shot)
Circular magnetization creates a field perpendicular to the bar's axis, making it most sensitive to longitudinally oriented (lengthwise) discontinuities.
Question 5: Which of the following is a characteristic of the 'near field' (Fresnel zone) in ultrasonic testing?
- Sound pressure is uniform and predictable
- Sound pressure varies erratically, making near-field inspection unreliable (Correct answer)
- Sound beam diverges widely
- Sensitivity is at its lowest
Correct answer: Sound pressure varies erratically, making near-field inspection unreliable
The near field is characterized by complex, erratic sound pressure variations that can cause false indications or missed defects.
Question 6: For radiographic testing of a butt weld, which ASME code parameter defines the maximum allowed geometric unsharpness (Ug)?
- Material tensile strength
- Material thickness being radiographed (Correct answer)
- Weld joint geometry
- Source isotope type
Correct answer: Material thickness being radiographed
ASME Section V Table T-285 specifies maximum Ug values based on the material thickness being radiographed.
Question 7: An eddy current probe shows a 'lift-off' signal. What does this indicate?
- The probe has detected a crack
- The probe is not in consistent contact with the test surface (Correct answer)
- The material has high conductivity
- The test frequency is too high
Correct answer: The probe is not in consistent contact with the test surface
Lift-off signal occurs when the probe-to-surface distance varies, causing a change in the coil's impedance that can mask true discontinuity signals.
CWI Nondestructive Examination Methods 5
What is the purpose of a couplant in contact ultrasonic testing?