Magnetic Particle Testing (MPI) in India: Principles, Practices & Applications

 


Contents

  1. What is Magnetic Particle Testing

  2. How MPI Works – Key Principles

  3. Equipment & Types of MPI Methods

  4. Indian Standards & Certification

  5. Applications in Indian Industries

  6. Advantages & Limitations

  7. Best Practices for India-based Users

  8. Conclusion

1. What is Magnetic Particle Testing

Magnetic Particle Testing (also called Magnetic Particle Inspection, MPI or MPT) is a Non-Destructive Testing (NDT) technique used to detect surface and near-surface discontinuities (defects) in ferromagnetic materials (iron, steel, some alloys). The test reveals cracks, laps, seams, voids, inclusions etc., by magnetising the part and then using fine magnetic particles that accumulate at leakage points in the magnetic field, making defects visually detectable. 

2. How MPI Works – Key Principles

Here’s the general process and the science behind MPI:

  • A ferromagnetic component is magnetised. When there is a crack or defect open or close to the surface, the magnetic flux will be disturbed or leak out at those points (flux leakage). 

  • Magnetic particles (either dry powder or suspended in liquid) are applied to the surface. These particles are attracted to the leakage field, forming visible indications. 

  • Visual inspection – under suitable lighting, sometimes UV light if fluorescent particles are used – is carried out to locate, size, and evaluate the defects. 

Kinds of Magnetisation:

  • Longitudinal / Continuous fields

  • Circular / Induced fields (using coils / central conductors / ring coils etc.)

  • Use of different magnetisation directions (often more than one, e.g. at right angles), to ensure defects in different orientations are revealed. 

Types of Particles:

  • Dry particles – coarser, easier to use in field conditions, visible particles. 

  • Wet particles – more sensitive, smaller size, especially fluorescent wet particles under UV light for greater contrast.

3. Equipment & Types of MPI Methods

Equipment

Some commonly used tools and setups include:

  • Yokes (portable) – for local magnetisation of parts or small areas. 

  • Coil magnetisers / central conductors – for parts that can be placed inside or wrapped around. 

  • Bench or tank magnetisation – for smaller parts or batch work.

  • Light sources – white light for visible, UV lamps for fluorescent particle inspections.

  • Dry powders & wet suspensions of magnetic particles.

Methods / Types

  • Visible / color contrast particles (dry or wet)

  • Fluorescent particles (wet) – require UV lighting and darker viewing environment

  • Application modes: particles applied during or after magnetisation

4. Indian Standards & Certification

To ensure consistency, reliability, safety, and technical compliance, Indian users of MPI adhere to various national and international standards.

Standard / CertificationWhat it Covers / Significance
IS 3703-2023 – Recommended practice for magnetic particle flaw detectionThe updated Indian standard giving guidelines for procedures, equipment, defect evaluation etc. 
ISO standards relevant (e.g. ISO 9934 series)Global standards for MPI, covering principles, detection media, equipment etc. (often used in Indian labs as reference) 
ISO 4986:2020 – for steel & iron castingsStandard for magnetic particle testing of ferro-magnetic castings, giving acceptance criteria for discontinuities. 
Certification of personnel / labsLevel I / Level II / Level III certification; many NDT training institutes in India (e.g. ANDT) offer MPI/MT courses. 
NABL / other accreditationFor labs offering inspection services, to confirm test results are accepted and trusted by clients.

5. Applications in Indian Industries

MPI is used extensively across Indian industries. Some sector-specific examples:

IndustryTypical Uses / Example Components
AutomotiveEngine blocks, crankshafts, camshafts, transmission components, welds in suspension systems. Detect cracks, laps, inclusions etc. 
Power Generation / Thermal Power PlantsTurbine shafts, boiler tubes, valves, generator components, weld joints in high stress zones.
Oil & Gas / PetrochemicalPipelines, storage tanks, welded joints, process equipment. MPI helps detect stress corrosion cracks, fatigue cracks, surface laps etc. 
Railways & InfrastructureAxles, wheels, structural steel, welds in bridges. Ensuring safety against crack propagation, fatigue.
Aerospace & DefenseCritical components (landing gear, engine parts) where failure has high risk. Need high sensitivity fluorescent MPI.
Fabrication / Welding WorkshopsInspecting weld beads, pre-service checks, qualification of welded parts. Portable MPI tools used often for in-situ checks.
Inspection ServicesMany service providers in Delhi NCR, Mumbai, Chennai etc providing field MPI/MPT services. Some labs offer both dry and wet fluorescent MPI. 

6. Advantages & Limitations

Advantages

  • Speed & immediacy – MPI gives relatively quick results. Useful for field or workshop inspection. 

  • Good sensitivity to surface and near-surface flaws; better than many methods for cracks just under the surface.

  • Equipment is often portable – yokes, dry powder, fluorescent wet suspensions etc. 

  • Can be less affected by certain surface conditions compared to, say, radiography; surface finish must be clean but not ultra-smooth.

Limitations

  • Only works on ferromagnetic materials. Non-ferrous or non-magnetic metals (like many stainless steels in austenitic phase) cannot be inspected by MPI.

  • Only surface and very near-surface defects; deeper internal flaws are not detected.

  • Surface preparation is important: paint, coatings, scale, grease etc. can hide defects.

  • After test, parts often need demagnetisation to remove residual magnetism.

  • Visibility & lighting constraints: fluorescent methods require UV light & environment control.

  • Safety and environmental concerns: handling of particles & suspensions, disposal, UV exposure etc.

7. Best Practices for India-based Users

To get reliable, repeatable results in the Indian industrial & environmental context:

  • Ensure your facility / inspection site has adequate lighting, especially if using fluorescent MPI.

  • Maintain surface cleanliness: remove rust, scale, coatings, oil, etc. If surface temperature or humidity is high (common in many Indian locations), manage those factors carefully.

  • Choose the appropriate magnetisation method & direction: multiple direction magnetisation may be needed to cover defects oriented in different ways.

  • Use correct type of particles (dry / wet, visible / fluorescent) based on component material, defect type, sensitivity required.

  • Ensure inspectors are trained & certified (Level I / II / III) as per IS / ISO / accepted bodies.

  • Maintain and calibrate equipment (yokes/coils etc.), check that magnetic field strength is adequate, workable.

  • Demagnetise after inspection if residual magnetisation could affect function or cause issues (e.g. in rotating parts).

  • Document procedures, results, defect characteristics, etc. Following IS 3703 or other standards helps in maintaining quality & acceptance by stakeholders.

8. Conclusion

Magnetic Particle Testing is a mature, reliable NDT method widely used in India. Its ability to quickly detect surface and near-surface defects in ferromagnetic materials makes it indispensable for safety, quality control, and maintenance across automotive, power, oil & gas, railways, aerospace, and many other sectors.

When used with the right standards (like IS 3703-2023), trained personnel, proper equipment, and good working conditions, MPI helps prevent failures, save cost, and assure integrity of critical components.

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