Magnetic Particle Testing 101: What You Need to Know

Magnetic particle testing provides one of the most reliable ways to test any metal structure.


Whenever you build or repair a product or structure, you do everything you can to deliver quality work. You don’t want that product to fail, and you certainly don’t want your work injuring anyone. This would weigh heavily on your conscience, not to mention spell disaster for your business. So, to ensure you provide quality work, you turn to non-destructive testing.

In previous blogs, we’ve addressed a few different non-destructive testing techniques. We’ve done this help you decide which techniques and teach you about how each technique works. However, we have yet to cover magnetic particle testing, which represents one of the most reliable ways to test any metal structure.

To learn more about this NDT technique, explore the information below.

How Does Magnetic Particle Testing Work?

The Basics

Magnets produce a field around them, with that field entering or exiting the magnet’s surface at two opposing poles. The poles have opposing charges, which create the flow of energy that generates the magnetic field.

If you break a magnet in half, the two halves become functioning magnets with opposing poles of their own. But magnetic particle testing takes advantage of another phenomenon – namely the phenomenon that occurs when you crack, but do not break the magnet.

When this happens, a north and south pole form at each edge of the crack, and since they have such a small gap between them, the air can’t handle it, so the magnetic field spreads out and becomes a flux leakage field.

So, when you magnetize a target surface, our experienced technicians at 20/20 NDT can simply detect the flux leakage fields to find flaws in your material.

The Process

Now that you know the science behind magnetic particle testing, you’d better understand what happens during the testing process. Our technicians at 20/20 NDT use a number of different processes when they use this technique, the most common being dry particle and wet suspension.

During dry particle magnetic inspections, professionals take the following steps:

  • They prepare the target surface. It shouldn’t have any contaminants on it, though this doesn’t matter as much as it would with other kinds of NDT. However, the target surface should always lack any water, oil, grease, or other liquid contaminants. However, you can keep a thin layer of paint on the surface.
  • They apply a magnetizing force. This many involve using permanent magnets or other electromagnetic devices, like coils, prods, or yokes. These materials make the target surface magnetic, at which point any flaws start producing flux leakage fields.
  • They apply or dust a layer of magnetic particles. These dry particles should move into the flux leakage fields.
  • They remove excess particles. This usually involves nothing more than simply blowing them off. This way, professionals can easily see where the particles cluster.
  • They inspect the area. If the professionals used an electromagnetic device, then they turn them off at this point. However, they may leave permanent magnets in place. Then they find all the areas where the particles gathered.

Wet suspension magnetic inspections involve similar steps:

  • They prepare the target surface. The same principles apply.
  • They apply the suspension. This usually means that they spray or pour it on.
  • They apply a magnetizing force. Immediately after applying the suspension, they apply force. This should make the suspension move.
  • They inspect the area. Again, the professionals will simply look for the places where the suspension gathered.

No matter what, don’t try this technique on your own unless you have years of experience with NDT. You want to get the most accurate reading possible, so you should leave the testing to the professionals.

What Advantages and Disadvantages Does This Technique Have?

Now that you know how magnetic particle testing works, you may wonder what makes it better than other NDT methods. This NDT technique has a number of advantages:

  • It helps you quickly inspect large surface areas and complex parts.
  • It can detect both surface and subsurface flaws.
  • It doesn’t require nearly as much preparation or cleanup as some methods.
  • It gives you an easily understood reproduction of the surface’s flaws rather than an abstract electronic signal.
  • The requisite equipment doesn’t cost as much as equipment for other NDT methods.

However, this doesn’t mean that magnetic particle testing doesn’t have flaws. You can only use to test ferromagnetic materials, which means mostly metals. You also have to get the magnetic field just right – which gives you another reason to leave this to the professionals. You also have to text relatively smooth surfaces with a limited amount of contaminants on them.

Still, this NDT technique can give you accurate and useful data when you need to test a product’s or structure’s integrity. To learn more about how magnetic particle testing can help your project, contact our helpful staff at 20/20 NDT. You can also read the rest of our blog for more information.