Super admin
. 17th Jun, 2025 5:27 PM
🧲 Magnetic Particle Inspection (MPI): How It Works and Where It Excels in NDT & QA/QC
What is Magnetic Particle Inspection
(MPI)?
Magnetic Particle Inspection (MPI) is a
non-destructive testing (NDT) method used to detect surface and near-surface
discontinuities in ferromagnetic materials (like iron, nickel, and cobalt).
It's widely used in Quality Assurance (QA) and Quality Control (QC) processes
in industries such as aerospace, automotive, oil & gas, and manufacturing.
⚙️ How MPI Works:
Step-by-Step
- Surface Preparation
The test surface must be clean and dry. Any grease, dirt, or scale is
removed to allow proper magnetization and particle flow.
- Magnetization
-
The part is magnetized using:
- Direct current (DC) or alternating current (AC)
- Methods include yokes, coils, central
conductors, or prods
This creates magnetic lines of flux in the
material.
- Application of Magnetic Particles
- Fine ferromagnetic particles, either dry or
suspended in liquid, are applied to the surface.
- Particles can be fluorescent (for UV light
inspection) or visible (for white light).
- Formation of Indications
- If a discontinuity (like a crack) is present, it
will interrupt the magnetic field, causing leakage fields.
- Magnetic particles are attracted to these
leakage fields, forming visible indications of the flaw.
- Inspection & Evaluation
- Inspectors examine the test area under
appropriate lighting (visible or UV).
- Indications are evaluated for size, shape, and
orientation to determine defect severity.
- Demagnetization and Cleaning
After inspection, the part is often demagnetized and cleaned, especially
if it's going back into service.
✅ Where MPI Excels
(Applications & Strengths)
🏭 Common Applications
- Weld inspection (structural steel, pressure vessels,
pipelines)
- Automotive: crankshafts, gears, axles
- Aerospace: landing gear, engine components
- Railway: axles, wheels
- Forgings and castings: surface defect checks
💪 Advantages
- Highly sensitive to small surface-breaking cracks
- Fast and relatively low-cost
- Works well on complex shapes and geometries
- Immediate results, often interpreted in real-time
- Can be used for in-service inspection
⚠️ Limitations of MPI
- Only works on ferromagnetic materials
- Detects mainly surface and near-surface flaws
- Surface prep is critical—contamination can mask
defects
- Requires skilled personnel for accurate
interpretation
- May require demagnetization after testing
🔧 MPI in QA/QC
Programs
In quality assurance and control, MPI is used:
- To verify weld integrity
- As part of incoming inspection on raw materials
or components
- For periodic maintenance checks in high-stress
components
- In final inspection before product delivery
MPI helps ensure components are defect-free, meet
industry standards, and prevent in-service failures—contributing to
safety, reliability, and compliance.
📞 Contact Details
For more information, inspections, or training services:
Make World Institute of Petroleum Bhopal
Email: info@makeworld.in
Phone: 9424347045, 0755-493-3347, 9424480384
Website: www.makeworld.in
