The typical use of magnetic particle inspection methods (a.k.a., MPI and MT) are to detect cracks, inclusions, seams, laps, and other discontinuities at or near the surface of ferromagnetic materials. Typical materials that fall into this category include "plain carbon steels" (i.e., ferrite matrix phase - those containing < .8% carbon), low grade stainless steel, cast iron, etc. [Note that a quick and easy test to determine the suitability of MPI is to place a magnet on the part. If the part is not magnetic, MPI is not an applicable test method.]

In general, MPI can be applied at any point during the manufacture and/or in-service use of a ferromagnetic part. MPI cannot be used on non-ferromagnetic materials or on parts with interfering coatings. Surface defects as small as .015" (.38mm) can be reliably detected with MPI. 
  

MPI applied to a ring shaped part (simulated, not under actual 
UV lighting)

We offer wet fluorescent, continuous and residual, as well as red oxide and black oxide visible dry powder methods of MPI. The most commonly used MPI method at our facility is wet fluorescent using an oil carrier. Please see our MPI literature for additional details of this technology.