Magnetic Particle Testing (MPI) is an effective non-destructive testing method used to detect surface and slightly subsurface cracks in ferromagnetic materials.
Surface and near-surface cracks in ferromagnetic castings — stress cracks, hot tears, grinding cracks, and fatigue cracks — are among the most dangerous defects because they act as stress concentrators under cyclic loading. Magnetic Particle Testing (MPI/MT) is the most sensitive and practical method for detecting these discontinuities in iron and steel components.
We apply MPI using both continuous and residual magnetisation techniques depending on material coercivity and part geometry. Magnetisation methods include yoke (AC and DC), prod, coil, and head-shot, selected based on the orientation of the suspected discontinuity relative to the component surface.
Wet fluorescent MPI (FMPI) using UV-A (black light) illumination provides maximum sensitivity for fine, tight cracks and is our standard method for critical components. Visible wet and dry methods are used for general production inspection where fluorescent processing is impractical.
All inspections conform to ASTM E1444, ASME Section V Article 7, EN ISO 17638 (weld inspection), and IS 3703. System performance checks (field indicator, pie gauge) are performed at the start of each inspection shift. Inspectors hold ASNT Level II or PCN Level II certification in MT.
Applicable to grey iron, ductile iron, cast steel, and forged steel components in automotive (crankshafts, brake drums, axle housings), heavy engineering, oil & gas, and defence applications where surface integrity certification is mandatory.
MPI is effective for surface-breaking and near-surface discontinuities up to approximately 3–4 mm depth below the surface. For deeper subsurface flaws, Ultrasonic Testing (UT) is required. The combination of MPI (surface) and UT (subsurface) provides comprehensive coverage for critical components.
No. MPI works only on ferromagnetic materials (iron, carbon steel, low-alloy steel, ductile iron, grey iron). Austenitic stainless steels, aluminium, copper alloys, and titanium are non-ferromagnetic and require Dye Penetrant Testing (DPT) for surface crack detection.
A single magnetisation direction detects cracks oriented perpendicular to the magnetic field. To ensure 100% coverage, we magnetise components in at least two perpendicular directions (biaxial inspection). For complex geometries, we map all critical zones and specify the magnetisation direction for each to guarantee complete surface coverage.
