Non-Destructive Testing - Magnetic Particle Inspection (MPI)

Question 1

Advantages of MPI

Answer 1

• Fast, simple and inexpensive
• direct, visible indication on surface
• unaffected by possible deposits, e.g. oil, grease or other metals chips, in the cracks
• can be used on painted objects
• surface preparation not required

Question 2

Limitations of MPI

Answer 2

• Works with Ferromagnetic materials only
• sub-surface defects will not always be indicated
• relative direction between the magnetic field and the
defect line is important
• objects must be demagnetized before and after the
examination
• current magnetization may cause burn scars on the
item examined

Question 3

Why is MPI one of the most widely utilised testing methods

Answer 3

Fast and relatively easy to apply with little surface preparation

Question 4

What varies the effectiveness of the MPI output?

Answer 4

The effectiveness of MPI depends strongly on the orientation of the crack related to the flux lines

Question 5

How is longitudinal magnetization created?

Answer 5

Longitudinal magnetization is achieved by means of a permanent magnet or an electromagnet

Question 6

How is circumferential magnetization created?

Answer 6

Circumferential magnetization is achieved by sending an electric current through the object

Question 7

How is an object directly magnetized?

Answer 7

Direct magnetization: A current is passed directly through the component

Question 8

How is an object indirectly magnetized?

Answer 8

Indirect magnetization uses a strong external magnetic field to establish a magnetic field within the component