NDT Magnetic Particle Testing Methods 4 — Questions and Answers
Question 1: Which type of indication in magnetic particle testing is caused by abrupt changes in cross-section or material permeability rather than a crack?
- Relevant indication
- Non-relevant indication (Correct answer)
- False indication
- Linear indication
Correct answer: Non-relevant indication
Non-relevant indications result from geometric features (threads, keyways, changes in cross-section) or permeability variations rather than actual discontinuities requiring rejection.
Question 2: A linear indication in magnetic particle testing is defined as one whose length is:
- Equal to its width
- Three times or more its width (Correct answer)
- At least 1/16 inch long
- Visible to the naked eye without magnification
Correct answer: Three times or more its width
A linear indication has a length-to-width ratio of 3:1 or greater, distinguishing it from rounded indications which have a ratio less than 3:1.
Question 3: What type of discontinuity is most likely indicated by a broad, fuzzy magnetic particle indication?
- A tight surface crack
- A subsurface discontinuity (Correct answer)
- A lap or fold on the surface
- A cold shut in a casting
Correct answer: A subsurface discontinuity
Subsurface discontinuities produce broader, less sharply defined (fuzzy) indications because the leakage field spreads as it reaches the surface above the defect.
Question 4: When evaluating magnetic particle indications, which factor most influences the decision to accept or reject a part?
- The color of the particles used
- The applicable code, standard, or acceptance criteria (Correct answer)
- The type of magnetization equipment used
- The experience of the inspector alone
Correct answer: The applicable code, standard, or acceptance criteria
Acceptance or rejection must be based on the applicable code, standard, or engineering specification that defines allowable indication sizes and types for the specific application.
Question 5: A 'hot crack' or 'crater crack' found in a weld during magnetic particle testing is best described as:
- A subsurface lamination in the base metal
- A solidification crack occurring in the weld metal during cooling (Correct answer)
- A hydrogen-induced crack forming days after welding
- A fatigue crack forming during service
Correct answer: A solidification crack occurring in the weld metal during cooling
Hot cracks (crater cracks) are solidification cracks that form in weld metal as it cools through the solidification temperature range, often found at weld terminations.
Question 6: What is the term for the condition where magnetic particle indications form at grain boundaries due to permeability differences, not actual defects?
- Magnetic writing
- Banding
- Non-relevant grain boundary indication (Correct answer)
- Seam indication
Correct answer: Non-relevant grain boundary indication
Non-relevant grain boundary indications occur when magnetic particles accumulate along grain boundaries due to permeability differences, not because of actual material discontinuities.
Question 7: Which discontinuity type is inherent to the raw material and typically aligned parallel to the material's working direction?
- Porosity
- Seams and laps (Correct answer)
- Undercut
- Lack of fusion
Correct answer: Seams and laps
Seams and laps are inherent material discontinuities originating during manufacturing (rolling, forging) that align parallel to the direction of metal working.
NDT Magnetic Particle Testing Methods 4
Which type of indication in magnetic particle testing is caused by abrupt changes in cross-section or material permeability rather than a crack?