Magnetic Particle Testing
Non-Destructive Testing: Magnetic Particle Testing (MT, MPI)
Magnetic particle testing (MT) is a fast, simple, and cost effect non-destructive testing technique that is capable of finding discontinuities in ferromagnetic metals. Compared to other non-destructive testing techniques, magnetic particle testing is the most reliable at finding surface and near surface discontinuities. Magnetic particle testing can detect inherent discontinuities such as ingot pipe, cold shuts, and hot tears as well as processing discontinuities such as seams in rolled bar and laminations in rolled plate. Lastly, magnetic particle testing is capable of finding in service discontinuities as well such as fatigue cracks that are caused by cyclically applied stress. Magnetic particle testing has four application methods, wet fluorescent, dual light, wet visual, and dry visual. The particles used in each method are made of a combination of iron and iron oxide with high permeability and low retentivity. Dry application particles are larger than wet applications with their particles being between 0.002” and 0.006” while wet method particles range from 0.0002” to 0.0006”. Each method has its own advantages and disadvantages and which method you choose for inspection is determine by a variety of factors.
Wet fluorescent magnetic particle (WFMT) testing is a non-destructive testing technique that uses magnetic particles suspended in either water or light oil distillate that has a high flash point. The media that the magnetic particles are suspended in reduce friction between the particles and the test surface allowing for greater particle mobility along the test surface. Greater particle mobility, even particle application, and the ability to find smaller cracks are all advantages of WFMT. To ensure all these advantages, the technician must confirm that their particle concentration is w