What Is Magnetic Particle Testing?
Magnetic Particle Testing (MT) — also referred to as Magnetic Particle Inspection (MPI) — is an
NDT method that detects surface and near-surface discontinuities in ferromagnetic materials by
applying a magnetic field and ferromagnetic particles (wet or dry) to the inspection surface.
Discontinuities that interrupt the magnetic flux lines cause flux leakage at the material surface —
and the magnetic particles collect at these flux leakage points, forming a visible indication that
reveals the location and orientation of the underlying defect.
Magnetisation Methods:
- Yoke magnetisation — portable electromagnetic yokes for field inspection of welds and
localised areas
- Prod magnetisation — contact prods for direct current magnetisation of plate and
structural sections
- Coil and cable wrap — longitudinal magnetisation for bar, shaft, and pipe sections
- Bench equipment — workshop MPI machines with head and coil shots for component
inspection in controlled environments
Particle Types:
- Wet fluorescent — highest sensitivity; particles applied in liquid suspension, examined
under UV-A illumination; required for many aerospace, energy, and critical fabrication
applications
- Wet visible (non-fluorescent) — black or red particles in liquid suspension; examined
under white light; suitable for general fabrication and structural inspection
- Dry powder — for elevated-temperature inspection and applications where wet methods
are not practicable