Magnetic Particle Testing
Magnetic particle testing is used to detect minute cracks or other damage in metal structure. The most common use tends to be in checking forks on forklifts and load bearing members on cranes and aerial devices. The process involves coating a dyed magnetic dust over the suspect area and using a electro-magnetic field to influence the dust. Any defects will change the natural shape of the magnetic field and it will show up in the dyed dust.
In some cases magnetic particle testing is not the ideal test method, at which point a dye penetrant will be used. A chemical penetrant is sprayed over an area and let to work it's way into cracks. After some time a developer is mixed with the penetrant changing the colour of the test area, any crack will be visible by a non-uniform colour.