NDT Nondestructive Testing Methods & Techniques 2 — Questions and Answers
Question 1: Which NDT method is most effective for detecting surface-breaking cracks in ferromagnetic boiler components?
- Liquid penetrant testing
- Magnetic particle testing (Correct answer)
- Radiographic testing
- Ultrasonic testing
Correct answer: Magnetic particle testing
Magnetic particle testing (MT) is ideal for detecting surface and near-surface discontinuities specifically in ferromagnetic materials like carbon steel boiler parts.
Question 2: In radiographic testing, what does a darker area on the developed film typically indicate?
- A denser region with fewer voids
- A thicker section of base metal
- A less dense region such as a void or porosity (Correct answer)
- A area with higher alloy content
Correct answer: A less dense region such as a void or porosity
Darker areas on radiographic film indicate less material density, meaning more radiation passed through — characteristic of voids, porosity, or cracks.
Question 3: What is the primary purpose of a calibration block in ultrasonic testing?
- To measure the thickness of the couplant layer
- To establish reference amplitude levels and distance measurements (Correct answer)
- To determine the chemical composition of the material
- To verify the power supply voltage of the UT instrument
Correct answer: To establish reference amplitude levels and distance measurements
Calibration blocks provide known reflectors (e.g., flat-bottom holes or notches) used to set reference gain levels and distance-amplitude correction curves for accurate flaw evaluation.
Question 4: A boilermaker performing liquid penetrant testing discovers bleed-out that appears as a broad, fuzzy indication. This most likely suggests:
- A tight, surface-breaking crack
- A subsurface lamination
- A wide, shallow surface discontinuity or porosity cluster (Correct answer)
- Correct penetrant dwell time was not achieved
Correct answer: A wide, shallow surface discontinuity or porosity cluster
Broad, fuzzy bleed-out typically indicates a wide-open surface discontinuity or cluster of porosity rather than a tight linear crack, which would produce a sharp line.
Question 5: When performing magnetic particle testing using the wet fluorescent method, inspection must be conducted under:
- Normal white light conditions above 100 foot-candles
- Ultraviolet (black) light with ambient white light below 2 foot-candles (Correct answer)
- Infrared light at wavelengths above 700 nm
- Daylight only to avoid UV exposure hazards
Correct answer: Ultraviolet (black) light with ambient white light below 2 foot-candles
Wet fluorescent MT requires UV-A (black) light to excite the fluorescent particles, and ambient white light must be below 2 foot-candles to maximize contrast of indications.
Question 6: In ultrasonic shear wave (angle beam) testing of a weld, the probe is typically positioned on the:
- Weld crown directly
- Base metal adjacent to the weld (Correct answer)
- Back surface of the plate
- Weld root only
Correct answer: Base metal adjacent to the weld
Angle beam probes are placed on the base metal beside the weld so the refracted shear wave can sweep through the weld volume at an angle to detect planar defects.
Question 7: Which of the following is a limitation of visual testing (VT) as an NDT method?
- It cannot detect surface conditions on the material
- It requires expensive and complex equipment
- It can only detect discontinuities open to the surface that are visible to the eye (Correct answer)
- It is only applicable to non-metallic materials
Correct answer: It can only detect discontinuities open to the surface that are visible to the eye
Visual testing is limited to surface-open discontinuities that are large enough to be seen by the naked eye or with optical aids; subsurface defects are not detectable.
NDT Nondestructive Testing Methods & Techniques 2
Which NDT method is most effective for detecting surface-breaking cracks in ferromagnetic boiler components?