CWI Nondestructive Examination Methods 4 — Questions and Answers
Question 1: Which NDE method is most effective for detecting subsurface discontinuities in a thick steel weld?
- Liquid penetrant testing
- Magnetic particle testing
- Ultrasonic testing (Correct answer)
- Visual testing
Correct answer: Ultrasonic testing
Ultrasonic testing can detect both surface and subsurface discontinuities at significant depths in steel welds.
Question 2: In ultrasonic testing, what does the term 'dead zone' refer to?
- Area beyond the maximum range of the transducer
- Region near the transducer face where near-surface defects cannot be detected (Correct answer)
- Area where the beam diverges past the near field
- Zone where couplant is not applied
Correct answer: Region near the transducer face where near-surface defects cannot be detected
The dead zone is the region immediately beneath the transducer face where the ringing of the crystal prevents detection of echoes from near-surface reflectors.
Question 3: What is the main advantage of using fluorescent penetrant over visible dye penetrant?
- Shorter dwell time required
- Greater sensitivity due to high contrast under UV light (Correct answer)
- No developer needed
- Can detect subsurface defects
Correct answer: Greater sensitivity due to high contrast under UV light
Fluorescent penetrant produces a bright glow under UV (black) light, providing significantly higher contrast and sensitivity compared to visible dye penetrant.
Question 4: A magnetic particle test is being performed on an austenitic stainless steel weld. Which statement is correct?
- MT can be performed as normal
- MT is not applicable because austenitic stainless steel is non-ferromagnetic (Correct answer)
- MT requires AC current only for this material
- MT requires wet particles only for this material
Correct answer: MT is not applicable because austenitic stainless steel is non-ferromagnetic
Austenitic stainless steels are non-ferromagnetic and cannot be magnetized, making MT inapplicable.
Question 5: In radiographic testing, which IQI type shows a series of wires of decreasing diameter?
- Hole-type IQI (plaque)
- Step-wedge IQI
- Wire-type IQI (Correct answer)
- Penetrameter strip
Correct answer: Wire-type IQI
Wire-type IQIs (also called wire penetrameters) consist of a set of wires of different diameters to indicate radiographic sensitivity.
Question 6: When conducting an eddy current test on a ferromagnetic material, what is often done to improve sensitivity?
- Increase test frequency
- Saturate the material with a DC magnetic field (Correct answer)
- Use a reflection probe
- Reduce the lift-off distance to zero
Correct answer: Saturate the material with a DC magnetic field
DC magnetic saturation suppresses the high magnetic permeability of ferromagnetic materials, reducing permeability noise and improving eddy current sensitivity.
Question 7: Which type of weld discontinuity would be LEAST likely to be detected by magnetic particle testing?
- Surface crack
- Subsurface crack at 6 mm depth (Correct answer)
- Near-surface porosity
- Toe crack
Correct answer: Subsurface crack at 6 mm depth
MT sensitivity decreases rapidly with depth; a subsurface crack at 6 mm is typically beyond the effective detection depth of MT.
CWI Nondestructive Examination Methods 4
Which NDE method is most effective for detecting subsurface discontinuities in a thick steel weld?