Which statement best describes a method to demagnetize after magnetic particle inspection?

Which statement best describes a method to demagnetize after magnetic particle inspection?

• A. Slowly moving the part out of an AC magnetic field
• B. Rapidly moving the part into a DC magnetic field
• C. Immersing the part in hot oil
• D. Cooling the part rapidly

Answer: (A)

Demagnetizing after magnetic particle inspection means removing residual magnetization so the part won’t attract ferrous particles or cause false indications. The best way to do this is to expose the part to an alternating-current (AC) magnetic field and move it away slowly as the field is reduced. The AC field continually reverses the magnetic domains, and as you gradually withdraw the part, the field strength falls to near zero, leaving the domains oriented randomly and the net magnetization vanishing. Moving the part quickly into a direct-current (DC) field would leave a strong, unidirectional magnetization, not demagnetization. Immersing in hot oil or cooling rapidly does not address the magnetic domains and won’t reliably remove residual magnetism.

Demagnetizing after magnetic particle inspection means removing residual magnetization so the part won’t attract ferrous particles or cause false indications. The best way to do this is to expose the part to an alternating-current (AC) magnetic field and move it away slowly as the field is reduced. The AC field continually reverses the magnetic domains, and as you gradually withdraw the part, the field strength falls to near zero, leaving the domains oriented randomly and the net magnetization vanishing. Moving the part quickly into a direct-current (DC) field would leave a strong, unidirectional magnetization, not demagnetization. Immersing in hot oil or cooling rapidly does not address the magnetic domains and won’t reliably remove residual magnetism.