Magnetic Particle Testing (MT)

1. What is Magnetic Particle Testing (MT)?

Magnetic Particle Testing is a non-destructive testing method used to detect discontinuities on the surface and in very close-to-surface substrates in ferromagnetic materials (such as iron, nickel, cobalt, and their alloys).
🔧 Basic Principle:
• The part to be inspected is magnetized (with direct current, alternating current, or half-wave AC).
• If a discontinuity (e.g., a crack) is present within the material, this discontinuity disrupts the flow of the magnetic field and creates flux leakage.
• When freely moving magnetic particles (dry powder or wet suspension) are applied to the area where the leakage flux occurs, these particles collect around the leakage area, creating a visual indicator.
💡 Application Methods:
• Dry powder method for surface defects (usually using AC current)
• Wet suspension method for near-surface defects (using DC or half-wave AC)
• Detection can be done with visible particles or fluorescent particles under UV light.
📏 Compatibility Requirements:
Applicable only to ferromagnetic materials.
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✅ 2. What are the advantages compared to other NDT methods?

It is very sensitive for surface and near-surface defects. It provides high sensitivity, especially for surface cracks.
It is a fast and practical application. Results can be obtained in the field in a very short time.
The results are visual. The defect location is directly visible thanks to the particles.
It is cost-effective. The equipment and consumables are relatively inexpensive.
It is compatible with complex geometries. It is suitable for welded joints, gear surfaces, cast parts, etc.
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🛠️ 3. What Defects Can This Method Detect?
Only discontinuities at the surface and 1–3 mm deep within the surface can be detected.

Surface cracks: This is the most sensitive type of defect (especially fatigue cracks).
Cold welding (lack of fusion): Weld defects on the surface are visible.
Solidification cracks: Superficial cracks that occur in cast parts.
Grinding cracks: Superficial microcracks caused by thermal stress.
Surface voids (porosity, inclusions): However, only those open to the surface are visible.
Surface-open mill cracks: Especially visible in rolled products.
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🏭 4. What is its Importance in Industry?
Magnetic particle testing is critical, especially in parts and joints containing ferromagnetic materials.
Sector and Areas of Use
Welded manufacturing sector: Post-weld surface crack inspection (e.g., cranes, bridges, pressure vessels).
Railway and automotive: Axles, wheels, suspension parts.
Aerospace and defense: Rotor shafts, gear systems.
Energy and nuclear: Turbine components, flanges, and welds on pipelines.
Casting and metalworking: Surface crack and mold defect inspection in steel castings.