MAGNETIC PARTICLE INSPECTION

What Is Magnetic Particle Inspection?

Magnetic particle inspection (MPI), also called magnetic particle testing (MT), is a non-destructive testing method that reveals surface and shallow subsurface discontinuities in ferromagnetic materials. When a component is magnetised, any crack, lap, seam or lack of fusion that interrupts the magnetic field forces some of that field to leak out at the surface. Fine iron particles applied to the part are drawn to this flux leakage and gather along the flaw, producing a visible indication that closely resembles the shape and position of the defect itself. Because the indication mirrors the real flaw, MPI is one of the fastest and most cost-effective ways to confirm the surface integrity of welds, castings and forgings.

How Magnetic Particle Inspection Works

The component is first magnetised using a yoke, prods, a coil or a central conductor, establishing a magnetic field within the material. Ferrous particles — supplied as a dry powder or suspended in a wet carrier, in visible or fluorescent form — are then applied to the surface. Where the field is undisturbed the particles wash away, but at a discontinuity the leakage field holds them in place to form an indication. Fluorescent particles viewed under UV-A (black) light give the highest sensitivity for fine cracks. Because flaws are only revealed when they lie across the magnetic field, the part is magnetised in at least two perpendicular directions to catch discontinuities in any orientation, and is demagnetised and cleaned afterwards where required.

Magnetic Particle Inspection Applications

MPI is used wherever cracking in steel could threaten safety or integrity: weld inspection on structural steel, pressure equipment and pipework; castings and forgings; crane hooks, lifting gear and rigging; shafts, axles and gears; and in-service inspection of mining, rail and heavy-industry components. It is a core surface method within a complete integrity program and is frequently run alongside ultrasonic inspection for volumetric coverage, dye penetrant inspection on non-magnetic materials, and visual inspection as the first line of assessment.

Australian Standards & Compliance

APEC performs magnetic particle inspection to the relevant Australian and international standards, including AS 1171 (magnetic particle testing of ferromagnetic products, components and structures), ISO 17638 for the testing of welds, and acceptance criteria from ISO 23278 or the applicable construction code such as AS 1554 for structural steelwork and AS/NZS 3788 for pressure equipment. All testing is carried out by technicians certified to AS 3998 / ISO 9712, so the inspection report stands up to client, regulator and insurer scrutiny.

MPI vs Dye Penetrant and Other NDT Methods

Magnetic particle inspection and dye penetrant inspection are the two main surface methods. MPI is faster, tolerates light surface contamination and can reveal flaws slightly below the surface, but it works only on ferromagnetic materials. Dye penetrant detects only surface-breaking flaws yet works on virtually any non-porous material, including austenitic stainless steel and aluminium. For defects deeper inside a component, volumetric methods such as ultrasonic or radiographic testing are required. Choosing the right combination is part of the inspection planning APEC provides for every job.

Why Choose APEC Inspection for Magnetic Particle Inspection

APEC Inspection is a NATA-accredited inspection body, and our magnetic particle inspection is carried out by AINDT-certified technicians who deliver clear, defensible reporting. We mobilise across Newcastle, the Hunter and nationally, and integrate MPI with the wider NDT and pressure vessel inspection services your assets need. To learn more about our non-destructive testing services, request a quote or call our team directly.