NDT Magnetic Particle Testing Methods 3 — Questions and Answers
Question 1: What is the key distinguishing characteristic of fluorescent magnetic particles compared to visible (dry) particles?
- They are larger and heavier for better adhesion
- They fluoresce under ultraviolet light, providing higher contrast (Correct answer)
- They work only with DC current
- They require oil-based carriers exclusively
Correct answer: They fluoresce under ultraviolet light, providing higher contrast
Fluorescent particles contain fluorescent dyes that glow brightly under UV-A (black) light, producing high contrast against the dark background and improving sensitivity.
Question 2: What is the typical UV-A wavelength range required for fluorescent magnetic particle inspection?
- 200–280 nm
- 315–400 nm (Correct answer)
- 400–500 nm
- 500–600 nm
Correct answer: 315–400 nm
UV-A light in the 315–400 nm range (with peak effectiveness near 365 nm) excites the fluorescent dyes in magnetic particles to produce visible indications.
Question 3: Which carrier liquid is preferred for fluorescent wet magnetic particle testing because it provides better particle mobility?
- Water-based conditioner (Correct answer)
- Light petroleum distillate (oil)
- Isopropyl alcohol
- Acetone
Correct answer: Water-based conditioner
Water-based conditioners (containing rust inhibitors and wetting agents) are often preferred for fluorescent wet MT because they provide excellent particle mobility and are environmentally friendlier than oil.
Question 4: What minimum ambient visible light level is required at the inspection surface when using fluorescent magnetic particles?
- Less than 20 foot-candles (200 lux)
- Less than 2 foot-candles (20 lux) (Correct answer)
- Less than 50 foot-candles (500 lux)
- Ambient light level does not matter
Correct answer: Less than 2 foot-candles (20 lux)
ASTM E1444 requires the ambient white light at the inspection surface to be no greater than 2 foot-candles (20 lux) so fluorescent indications are clearly visible under UV-A light.
Question 5: When should the concentration of fluorescent magnetic particle bath be checked?
- Only at the start of each work week
- Before each inspection shift and after replenishment (Correct answer)
- Once per month during scheduled maintenance
- Only when indications seem unclear
Correct answer: Before each inspection shift and after replenishment
Bath concentration should be verified before each inspection shift and after replenishing the bath to ensure consistent sensitivity throughout the inspection process.
Question 6: What is the ASTM E1444 acceptable fluorescent particle bath concentration range when measured using a centrifuge tube (pear-shaped)?
- 0.1–0.4 mL per 100 mL
- 0.2–2.4 mL per 100 mL (petroleum vehicle) or 0.1–0.4 mL (water) (Correct answer)
- 1.0–4.0 mL per 100 mL
- 2.0–6.0 mL per 100 mL
Correct answer: 0.2–2.4 mL per 100 mL (petroleum vehicle) or 0.1–0.4 mL (water)
ASTM E1444 specifies 0.1–0.4 mL per 100 mL for water-conditioned bath and 0.2–2.4 mL per 100 mL for petroleum-based bath as acceptable concentration ranges.
Question 7: Dry magnetic particles are most commonly used in which application?
- Underwater inspection of submerged structures
- Field inspection of welds and castings at elevated temperatures (Correct answer)
- High-volume automated production line inspection
- Detection of very fine subsurface cracks
Correct answer: Field inspection of welds and castings at elevated temperatures
Dry particles are preferred for field inspection of rough-surface welds and castings, especially at elevated temperatures where wet bath methods are impractical.
NDT Magnetic Particle Testing Methods 3
What is the key distinguishing characteristic of fluorescent magnetic particles compared to visible (dry) particles?