Magnetic Particle Examination
An inspection method used to detect defects that are exposed to the surface — or hiding just below it. Where the material breaks its own magnetic path, the indication appears.
What it is and how it works.
Magnetic particle testing is an inspection method used to detect defects that are exposed to the surface or just below the surface of ferromagnetic materials. The underlying principle involves applying either magnetic flux — magnetic flow techniques — or current — current flow techniques — to the inspection surface.
When a discontinuity exists, the magnetic waves overflow by condensing on the material surface — leakage flux. Auxiliary equipment such as background paint and iron powder makes these discontinuities visible and detectable to the examiner.
The method at a glance.
Surface and near-surface defects — cracks, laps, seams and inclusions in ferromagnetic materials.
Magnetic flux or current is applied to the surface; leakage flux at a discontinuity gathers iron powder into a visible indication.
Welds, castings and forgings in steels where fine surface-breaking cracks must not be missed.
A method with a long record.
The techniques behind this examination were earned over more than a century of engineering.
British observer S.M. Saxby notes that magnetised gun barrels affect compasses — the first recorded observation of magnetic indication.
Saxby, and later American William Hoke, attempt to locate cracks in gun barrels using magnetic indications.
The first industrial application of the method by Victor de Forest and Foster Doane.
De Forest and Doane found the company known as Magnaflux — magnetic particle inspection enters industry for good.
Where this method earns its keep.
Typical components and industries we examine with this technique, across our country-wide network.