What is the principle behind Magnetic Particle Testing?
Magnetic Particle Testing is based on the principle of magnetic flux leakage.
When a ferromagnetic material is magnetized, magnetic field lines flow through it.
If there is a discontinuity such as a crack, the magnetic field is disturbed, causing leakage at that point.
Magnetic particles applied to the surface are attracted to these leakage fields, forming visible indications.
The direction of magnetisation is important and should be perpendicular to the defect orientation for best results.
How does Magnetic Particle Testing work?
The test object is magnetised using a yoke, coil, or prods. Magnetic particles (dry powder or wet suspension) are applied to the surface. If defects are present, particles accumulate at those locations, forming visible patterns. Fluorescent particles are viewed under UV light for enhanced visibility.
What equipment is used in Magnetic Particle Testing?
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Magnetic yoke (AC/DC)
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Prods and coils
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Bench-type MT machines
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Dry magnetic powder or wet fluorescent particles
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UV lamp (365 nm) for fluorescent testing
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White contrast paint
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Gauss meter and field indicators (pie gauge)
How do you prepare for Magnetic Particle Testing?
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Clean the surface (remove oil, grease, paint, rust)
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Apply contrast paint if required
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Select appropriate magnetization technique
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Ensure proper lighting conditions (white light or UV light)
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Magnetize the component
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Apply magnetic particles
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Demagnetise the component after inspection inspection
How are Magnetic Particle Testing results interpreted?
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Indications are directly visible on the surface
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Linear indications → cracks (generally rejectable)
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Rounded indications → porosity or non-relevant
Standards used:
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ASME Section V Article 7
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ASTM E709
Results are:
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Photographed and documented
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Recorded in inspection reports or Excel
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Stored digitally for traceability
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What is Magnetic Particle Testing (MT)?
Magnetic Particle Testing (MT) is a non-destructive testing method used to detect surface and near-surface defects in ferromagnetic materials. It works by magnetising the component and applying magnetic particles that gather at defect locations, making them visible. MT is widely used for weld inspection and structural components.
What is Magnetic Particle Testing used for?
Magnetic Particle Testing is used to detect surface and near-surface cracks quickly and effectively. It is especially useful for weld inspection and fatigue crack detection. It is more sensitive than penetrant testing for ferromagnetic materials. Common applications of MT are in Weld Inspection, Crane Hooks & Lifting Equipment and Pipeline Girth Welds.
Which industries use Magnetic Particle Testing?
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Oil & Gas
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Aerospace
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Automotive
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Structural Steel
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Railways
When should you use Magnetic Particle Testing?
Use Magnetic Particle Testing when:
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Material is ferromagnetic (carbon steel, low alloy steel)
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Surface or near-surface defects need detection
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Fast inspection is required
When should you not use Magnetic Particle Testing?
Avoid MT when:
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Non-ferrous materials (aluminium, stainless steel, copper)
What are the advantages and limitations of Magnetic Particle Testing?
Magnetic Particle Testing is fast, cost-effective, and highly sensitive for surface cracks. However, it is limited only to ferromagnetic materials and requires proper surface preparation. Post-inspection cleaning and demagnetisation are also necessary.
Avantages:
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Safety
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No radiation hazard
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Safe for on-site inspections
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Speed
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Very fast inspection
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Immediate visible results
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Minimal setup time
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Access
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Portable equipment (yoke, prods)
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Suitable for field use
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Works on complex shapes
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Storage
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Easy photo documentation
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Can be digitised for reporting
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Limitations:
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Safety
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Requires handling of magnetic fields
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UV light precautions needed (for fluorescent testing)
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Speed
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Demagnetisation required after inspection
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Access
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Only works on ferromagnetic materials
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Defect orientation affects detectability
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Storage
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No inherent permanent record
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Depends on proper documentation
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