Magnetic Particle

Surface Inspection of Ferromagnetic Materials

Magnetic Particle Inspection (MPI), also known as Magnetic Particle Testing (MT), is an efficient, cost effective and reliable non-destructive test method for detecting critical flaws in ferromagnetic[i] materials.

Generally applied as a surface inspection[ii] on carbon steels and other alloys that can be magnetized, magnetic particle inspection can accurately reveal flaws that normal visual inspection cannot detect including:

  • cracks
  • seams
  • laps
  • fusion discontinuities

Higher stress loads and most severe flaws are generally concentrated on the outer surfaces of components than in their interior volume. Therefore, enhanced surface inspection processes such as magnetic particle and liquid penetrant testing are crucial to flaw detection and failure prevention.

Quality Control Applications

Applications for magnetic particle inspection include testing welds, castings, tools, bar-stock, and other components for quality control, surface integrity, code conformance and pre-machine screening.

Magnetic Particle Inspection Process

When materials are magnetized by direct electric current or induction from magnetizing coils and hand held yoke-type solenoids, lines of magnetic force (or flux) - similar to the magnetic fields of permanent magnets and the Earth itself – are interrupted by material flaws and material changes.

Flaws on (or slightly below) metal surfaces cause a leakage in the applied magnetic field that draws very fine, sensitive, colored or fluorescent particles to the discontinuity.

Indications formed by particles attracted to these flaws can be evaluated by our trained and certified technicians for code acceptance or failure, surface integrity, and to ensure reliable service of components subjected to stress and wear.

Magnetic particle testing is often used in conjunction with, or in support of, other non-destructive test methods at Baker Testing Services labs and in on-site applications.

Multiple magnetizing devices, methods, particle types, sensitivities and application methods can be tailored to product requirements and code conformance in support of power generation, welding, foundry, engineering, construction, manufacturing and failure prevention applications.

Qualified Inspection Technicians

  • Large and small parts or components can be inspected in accordance with ASME, AWS, MIL-STD, AMS, ASTM codes or specifications as well as customer specific requirements.
  • Baker Testing Services has technicians with over 35 years of diversified experience in Magnetic Particle Testing and other NDT methods to provide expert inspection for most any application.
  • Our experienced Level II and Level III personnel are trained and certified to ASNT-TC-1A, CP-189 and MIL-STD-410/NAS 410 requirements.
  • BTS qualifications and procedures conform to ASTM and Military specifications, and are accepted by customers in many diverse fields and applications.
  • Veriforce Operator Qualified (OQ)

[i] Ferromagnetic materials such as iron, nickel, cobalt and other alloys with relatively high iron (Fe) content allow them to be magnetized. Magnetic permeability is the term used for the ability of a material to be magnetized; it varies with different alloys.

[ii] While MT is a highly sensitive surface inspection method, especially when using AC current, some shallow material flaws can be detected using DC current depending on flaw type, size, and material permeability.

  • Not visible to the eye, weld cracks become exposed when florescent is applied to the surface; magnetic particles accumulate in the crack.
  • Inspection of an I-Beam weld involves use of a contour probe, known as a yoke, that magnetizes the weld.
  • In the test laboratory, wet florescent causes forging laps and cracks to become visible in a dark environment.