Magnetic Particle Testing (MPT), also referred to as Magnetic Particle Inspection, is a non-destructive examination (NDE) technique used to detect surface and slightly subsurface flaws in most ferromagnetic materials such as iron, nickel, and cobalt, and some of their alloys. Because it does not necessitate the degree of surface preparation required by other nondestructive test methods, conducting MPT is relatively fast and easy. This has made it one of the more commonly utilized NDE techniques.
This involves magnetizing them in order to reveal flaws that would not normally be apparent. MPT is fast and easy to apply in part because surface preparation is not as critical as it is for some other NDE methods. Because of this, it is one of the most commonly used NDE techniques and can be utilized to inspect a variety of ferromagnetic product forms including castings, forgings, and weldments for fitness-for-use.
MPT has been in use for many decades now and in that time has seen a number of advancements and improvements, yet it has still remained one of the simplest and most effective methods for detecting surface flaws in ferromagnetic materials.
There are several benefits of MPT compared to other NDE methods. It is highly portable, generally inexpensive, and does not need a stringent pre-cleaning operation. MPT is also one of the best options for detecting fine, shallow surface cracks. It is fast, easy, and will work through thin coatings. There are a few limitations regarding the size/shape of test specimens.
Despite its strengths, the method is not without its limits. The material must be ferromagnetic. Likewise, the orientation and strength of the magnetic field is critical. The method only detects surface and near-to-surface defects. Those further down require alternative methods. Large currents are sometimes required to perform this method, thus “burning” of test parts is sometimes possible. In addition, once MPT has been completed, the component must be demagnetized, which can sometimes be difficult.