AWS Certified Welding Inspector — FundamentalsNondestructive Examination (NDE)Medium
A CWI is evaluating a Magnetic Particle Testing (MT) indication on a ferromagnetic weld. The indication appears as a broad, fuzzy, and indistinct line that does not follow any specific weld feature or heat-affected zone boundary. What is the MOST likely cause of this type of indication?
- AA surface breaking fatigue crack.
- BInsufficient magnetic field strength.
- CA subsurface crack.
- DMagnetic writing (non-relevant indication).
Show answer & explanationAnswer & explanation
Correct answer: D. Magnetic writing (non-relevant indication).
Broad, fuzzy, and indistinct indications that do not correlate with actual discontinuities are often 'magnetic writing' or other non-relevant indications. These can be caused by friction, grinding, or impacts during handling, which leave residual magnetism or localized magnetic fields that attract particles.
Why the other options are wrong
- A. Surface breaking fatigue cracks usually produce sharp, clear, and well-defined linear indications.
- B. Insufficient magnetic field strength would result in no indications or very weak indications from actual defects, not broad, fuzzy non-relevant ones.
- C. Subsurface cracks typically produce less defined, broader indications than surface cracks, but are still usually more distinct than 'magnetic writing'.
MT - Magnetic Writing
Magnetic writing is a non-relevant indication in Magnetic Particle Testing (MT) that appears as broad, fuzzy, or indistinct lines, often caused by localized magnetism from friction or impact, rather than a material discontinuity.
- Non-relevant indication.
- Caused by localized residual magnetism.
- Appears broad, fuzzy, indistinct.
- Does not represent a defect.
Memory trick: Sharp lines mean cracks, fuzzy lines often mean friction.