A closer look at MPI

Magnetic Particle Inspection

Surface or near-surface flaws in metals, metal products, and welds can cause serious issues. Even a small crack is a weak spot that over time could result in failure. With this in mind, it is absolutely crucial to do testing to determine if there are any flaws. One of the methods you could use here is magnetic particle inspection (MPI).

What is it?

MPI is a form of non-destructive testing that can effectively determine the location, size, and shape of surface and near-surface flaws. It provides very fast results and will also show flaws in their exact location on the surface of the specimen.

How does it work?

The technique is a really interesting one. It relies on the use of fine ferromagnetic particles, generally iron ones because of their high magnetism. They are spread carefully over an area, generally as dry particles or suspended in ink. Then the item is magnetised. If the material is sound, the flux will remain within the metal. However, if there is a crack, no matter how fine, it will cause the magnetic field to distort and leak around the flaw. This in turn will disturb the particles on the surface, showing exactly where the flaw is.

Magnetic particle inspection is great for detecting flaws in metals that can be strongly magnetised. This includes iron, ferritic steels, and nickel. However, it is not suitable for any metal with low magnetism.


There are a number of noteworthy advantages with MPI.

  • Firstly, as we said above it can provide very fast and accurate results. This includes giving a good idea of the shape and size of any flaws.
  • On top of that, this type of testing is very easy and appropriate for inspecting parts with irregular shapes.
  • In addition, portable equipment means it is possible to do the testing in various locations.

Come to us for magnetic particle inspection

Format NDT Ltd has a lot of experience with MPI. We have qualified inspections and top of the line equipment. We can arrange to conduct the testing on your site or in-house within our laboratory. This gives our clients more options so they can choose the right service for them.

If you have any questions about magnetic particle inspection, please contact us. We are happy to offer advice and can also use other methods of non-destructive testing if the materials are non-ferromagnetic.