Magnetic Particle Inspection

Question 1

What defects can magnetic particle examination detect?

Answer 1

Surface and near surface discontinuities

Question 2

What materials can magnetic particle inspection be applied to?

Answer 2

Ferromagnetic; materials such as Nickel, Iron, Cobalt or alloys of the elements listed above

Question 3

Why can’t MPI be used on austenite?

Answer 3

Austenite is non-magnetic therefore needs to be inspected with liquid penetrant

Question 4

What are the 2 classes of magnetization fields and what are their characteristics?

Answer 4

1) Circular: an electric current passes through a specimen and a circular magnetic field is produced

2) Longitudinal: an electric current is passed through a solenoid or coil to establish a longitudinal magnetic field in the material.

Question 5

What types of devices produce circular magnetic fields?

Answer 5

1) Prods
2) Head shot
3) Central conductor

Question 6

What types of devices produce a longitudinal magnetic field?

Answer 6

1) Permanent magnet
2) Yoke
3) Coil

Question 7

What are the 2 types of testing mediums used in MPI?

Answer 7

1) Dry, magnetic powder: most commonly used on hot, rough surfaces and welds and castings to prevent quenching

2) Liquid medium: uses a fluorescent dye that glows under a blacklight. The most sensitive method due to liquid getting into defects very well

Question 8

What is the procedure for conducting MPI?

Answer 8

1) Clean and degrease the working surface
2) Apply the magnetizing force to the specimen
3) Introduce magnetic particles to the surface
4) Conduct inspection
5) After the inspection the part is demagnetized

Question 9

To ensure detectability the magnetic field has to be oriented _______________ to the defect.

Answer 9

Perpendicular

Question 10

What are some advantages of MPI?

Answer 10

1) Can detect surface and subsurface defects
2) Can inspect irregular shapes
3) Fast
4) Can be portable
5) Defects are seen on the specimen
6) Considered low cost compared to other methods

Question 11

What are some disadvantages of using MPI?

Answer 11

1) Can not inspect non-ferrous metals like Aluminum, SS, and Magnesium
2) Surface preparation is required
3) Surface cleaning and demagnetization is required after the test
4) Alignment between magnetic flux and the defect is crucial

Question 12

What is the difference between residual ad continuous methods and which one is more common?

Answer 12

Residual method: the medium is applied after the magnetizing force has been removed

Continuous method: the application of a medium and the magnetizing force are conducted simultaneously. This is the most common method.