Magnetic particle inspection (MT) is a non-destructive testing method used to detect surface and slightly subsurface flaws in ferromagnetic materials (such as carbon steel).  It is used routinely to inspect welds, piping, pressure vessels and structural steel components. 


  • New fabrication welds for code compliance to:
  • ASME Section V for pressure vessels
  • ASME B31.1 and B31.3 for piping
  • API 1104 for pipelines
  • Castings and forgings, valves and their components, machined parts, pressure vessels, cranes and structural steel welds for cracks, non-fusion, cold laps
  • In-service welds



  • 1. Flaws are highly visible
    2. The equipment is:
  • Portable and can be battery powered
  • Light enough to take easily onto scaffolding
  • Non-hazardous to operations or other nearby personnel
  • Has no effect on equipment or materials in the vicinity
  • Very good sensitivity to fatigue cracking, tight fusion, HIC and SCC



  • Surface must be accessible and must be clean and free from oil, grease, scale, etc
  • Cannot detect deep subsurface flaws
  • Instrumentation and aircraft components require demagnetization after being inspected; residual magnetization may cause them to malfunction
  • May require a power supply that is not intrinsically safe


The area to be inspected is prepared and ferrous iron particles are applied to the part. The particles may be dry or in a wet suspension. The piece is then magnetized by direct or indirect magnetization, whereas the presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak.  If an area of flux leakage is present the ferrous particles will be attracted to this area, resulting in an indication. Test results are interpreted in accordance with the appropriate specifications, or customer requirements. A detailed report is issued clearly identifying the locations of any discontinuities.


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