page_title: Magnetic particle inspection
section_title: Magnetic particle powder
hierarchical_section_title: Magnetic particle inspection / Magnetic particle powder
caption_attribution_description: English: PACIFIC OCEAN (Dec. 20, 2010) Aviation Structural Mechanic 1st Class Charles Martens, a non-destructive inspection (NDI) technician, uses ultraviolet light to inspect a bolt during a magnetic particle inspection in the NDI shop aboard the aircraft carrier USS Carl Vinson (CVN 70). Carl Vinson and Carrier Air Wing (CVW) 17 are on a three-week composite training unit exercise to be followed by a deployment to the U.S. 7th and U.S. 5th Fleet areas of responsibility. (U.S. Navy photo by Mass Communication Specialist 2nd Class James R. Evans/Released)
context_page_description: Magnetic particle Inspection is a non-destructive testing process for detecting surface and shallow subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines of force are perpendicular to the direction of the electric current, which may be either alternating current or some form of direct current.
  The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak, since air cannot support as much magnetic field per unit volume as metals.
  To identify a leak, ferrous particles, either dry or in a wet suspension, are applied to a part.
context_section_description: A common particle used to detect cracks is iron oxide, for both dry and wet systems.
  Wet system particle range in size from less than 0.5 micrometres to 10 micrometres for use with water or oil carriers. Particles used in wet systems have pigments applied that fluoresce at 365 nm (ultraviolet A) requiring 1000 μW/cm² (10 W/m²) at the surface of the part for proper inspection. If the particles do not have the correct light applied in a darkroom the particles cannot be detected/seen. It is industry practice to use UV goggles/glasses to filter the UV light and amplify the visible light spectrum (normally green and yellow) created by the fluorescing particles. Green and yellow fluorescence was chosen, because the human eye reacts best to these colors.
  Dry particle powders range in size from 5 to 170 micrometres, designed to be seen in white light conditions. The particles are not designed to be used in wet environments. Dry powders are normally applied using hand-operated air powder applicators.
  Aerosol applied particles are similar to wet systems, sold in premixed aerosol cans similar to hair spray.
caption: After applying wet magnetic particles, a U.S. navy technician examines a bolt for cracks under ultraviolet light.
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