Non-Destructive Testing (NDT) Practice Test

What type of current should be used to demagnetize a part after a magnetic particle inspection?

1. DC

2. AC

3. Pulsating current

4. Standard current

The correct answer is: AC

The correct type of current to use for demagnetizing a part after a magnetic particle inspection is alternating current (AC). This is primarily because AC can effectively reduce the residual magnetic field in the part. When alternating current is applied, the magnetic field it creates regularly switches direction, which helps in neutralizing any remaining magnetism in the material. The process involves passing the part through a coil energized with alternating current, which gradually reduces the strength of the magnetism until it is completely demagnetized. This is essential as leftover magnetism could interfere with further inspections or the proper functioning of the component in actual service conditions. In contrast, direct current (DC) tends to maintain the magnetic polarity rather than alternating it, which may leave some residual magnetism. Pulsating current may not provide the consistent effectiveness needed for thorough demagnetization, and standard current does not specify a type that falls into either category, making it less appropriate for the task at hand. Therefore, using alternating current is universally recognized as the most reliable method for demagnetizing components post-inspection.