Introduction
In industries like oil & gas, manufacturing, energy, marine, and construction, safety and structural integrity are non-negotiable. One of the most efficient methods to detect surface and near-surface defects in metal components is Magnetic Particle Inspection (MPI)—a widely used technique in the field of Non-Destructive Testing (NDT).
What is Magnetic Particle Inspection (MPI)?
Magnetic Particle Inspection is a non-destructive testing method used to detect cracks, seams, inclusions, or other discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys.
The technique works by inducing a magnetic field into the component. If there are any defects, they interrupt the magnetic field, causing leakage fields. When iron particles (in dry powder or wet suspension form) are applied, they gather around the leakage, making the defect visible under proper lighting or UV light.
Key Benefits of MPI
- ✅ Non-Destructive: No damage to the part or material tested
- ✅ Fast and Efficient: Ideal for high-volume inspections
- ✅ Cost-Effective: Requires minimal equipment and consumables
- ✅ Highly Sensitive: Detects both surface and slightly subsurface flaws
- ✅ Field-Test Friendly: Can be performed on-site or in workshops
Common Applications of MPI
- Oil and Gas Pipelines
- Welded Structures
- Pressure Vessels and Tanks
- Offshore Platforms
- Shipbuilding Components
- Automotive and Aerospace Parts
- Heavy Machinery and Cranes
The MPI Process: Step-by-Step
- Surface Preparation
Remove oil, grease, paint, or rust to ensure accurate results. - Magnetization
Apply magnetic current through a coil, yoke, or prods. - Application of Magnetic Particles
Apply dry powder or wet suspension—either fluorescent or visible. - Inspection
Use visible light or UV light to identify particle indications. - Demagnetization and Cleaning
Remove residual magnetism and clean the part for future use.
MPI vs Others NDT Method
| Technique | Material Type | Surface/Depth | Portability | Cost |
|---|---|---|---|---|
| MPI | Ferromagnetic Only | Surface & Near Surface | High | Low |
| UT | All materials | Subsurface | Medium | Medium |
| PT | All non-porous materials | Surface only | High | Low |
| RT | All materials | Surface & Internal | Low | High |
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