NDT Magnetic Particle Testing Methods 2 — Questions and Answers
Question 1: Which magnetization technique is most effective for detecting longitudinal discontinuities in a cylindrical bar?
- Circular magnetization using a central conductor (Correct answer)
- Longitudinal magnetization using a coil
- Yoke magnetization along the bar axis
- Prod magnetization perpendicular to the bar
Correct answer: Circular magnetization using a central conductor
Circular magnetization creates a magnetic field circumferentially around the part, which is perpendicular to longitudinal discontinuities and maximizes their detection.
Question 2: What is the purpose of the 'residual method' in magnetic particle testing?
- Magnetizing the part while applying particles
- Applying particles after the magnetizing current is turned off (Correct answer)
- Demagnetizing residual fields before inspection
- Checking residual particle adhesion after testing
Correct answer: Applying particles after the magnetizing current is turned off
The residual method applies particles to a part after magnetization is complete, relying on the retained residual magnetic field to hold particles at discontinuity locations.
Question 3: When using the continuous method of magnetic particle testing, particles are applied:
- Before magnetization begins
- While the magnetizing current is flowing (Correct answer)
- After the magnetizing current is turned off
- After demagnetization
Correct answer: While the magnetizing current is flowing
In the continuous method, magnetic particles are applied while the magnetizing current is actively flowing, taking advantage of the stronger applied field rather than only residual magnetism.
Question 4: A head shot (contact shot) in magnetic particle testing produces which type of magnetization?
- Longitudinal
- Circular (Correct answer)
- Multidirectional
- Residual only
Correct answer: Circular
Passing current directly through the part between head contacts creates circular (circumferential) magnetization around the part's cross-section.
Question 5: What is the primary advantage of multidirectional magnetization in magnetic particle testing?
- Stronger magnetic field than single-direction methods
- Detection of discontinuities in multiple orientations in one operation (Correct answer)
- Elimination of the need for demagnetization
- Better particle adhesion on rough surfaces
Correct answer: Detection of discontinuities in multiple orientations in one operation
Multidirectional magnetization sequences through different field directions rapidly, allowing detection of variously oriented discontinuities without repositioning the part.
Question 6: When using prod magnetization, what is the recommended current range per inch of prod spacing according to ASTM E1444?
- 50–100 amperes per inch
- 100–125 amperes per inch (Correct answer)
- 150–200 amperes per inch
- 200–300 amperes per inch
Correct answer: 100–125 amperes per inch
ASTM E1444 specifies 100–125 amperes per inch of prod spacing as the standard current range for prod magnetization of most materials.
Question 7: Which of the following best describes 'swinging field' magnetization?
- Alternating the polarity of a yoke during inspection
- Rapidly switching between two or more directional fields to detect all orientations (Correct answer)
- Using a hand-held yoke moved in an arc pattern
- Applying AC then DC current in sequence
Correct answer: Rapidly switching between two or more directional fields to detect all orientations
Swinging field (multidirectional) magnetization rapidly cycles the field through multiple directions so that all discontinuity orientations are detectable in a single inspection step.
NDT Magnetic Particle Testing Methods 2
Which magnetization technique is most effective for detecting longitudinal discontinuities in a cylindrical bar?