AWS Certified Welding Inspector — FundamentalsNondestructive Examination (NDE)Medium
A CWI is performing a Magnetic Particle Testing (MT) inspection on a large ferritic steel casting using the wet fluorescent method. The CWI notices that the magnetic particle indications appear fuzzy and spread out, making it difficult to clearly define the discontinuities. What is the most likely cause of this issue?
- AImproper lighting conditions for fluorescent inspection.
- BInsufficient magnetic field strength.
- CUsing a non-ferromagnetic prodding tip.
- DExcessive concentration of magnetic particles in the suspension.
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive concentration of magnetic particles in the suspension.
An excessive concentration of magnetic particles in the suspension can lead to particle agglomeration and a 'fuzzy' or smeared appearance of indications, as too many particles are attracted to even minor flux leakage fields, obscuring the true shape of the discontinuity.
Why the other options are wrong
- A. Improper lighting affects visibility of indications but doesn't inherently cause them to be fuzzy or spread out.
- B. Insufficient magnetic field strength would result in weak or no indications, not fuzzy, spread-out ones.
- C. Using a non-ferromagnetic prodding tip would prevent the introduction of unwanted magnetic fields, which is correct practice, not a cause of fuzzy indications.
Magnetic Particle Concentration
The amount of magnetic particles (by volume) suspended in the carrier fluid for wet MT.
- Crucial for clear, sharp indications.
- Too high: fuzzy, smeared indications, high background.
- Too low: weak or missed indications.
- Checked regularly using a centrifuge tube.
Memory trick: Fuzzy indications mean too many particles, like too many sprinkles on a donut.