Magnetic Particle Inspection (MPI)

Magnetic Particle Testing is used for detecting surface and near-surface defects in ferromagnetic materials. A magnetic field is applied to the material, and magnetic particles are applied to the surface. The particles accumulate at areas of magnetic field distortion, highlighting defects such as cracks. MPI is used to detect surface breaking, or very near surface, defects on ferromagnetic materials only. MPI involves applying a magnetic field to a material and then applying magnetic particles to the surface. Discontinuities in the material cause the particles to accumulate, indicating the presence of a flaw.

Key advantages of Magnetic Particle Inspection

• Sensitivity to Surface Discontinuities: MPI is highly sensitive to surface and near-surface defects, making it effective for detecting cracks and other discontinuities that may affect the integrity of a component.

• Quick and Cost-Effective: The inspection process is relatively quick, and the equipment is often portable, making it a cost-effective method for routine inspections.
• Suitability for Field Inspections: MPI can be performed in the field, making it suitable for inspecting structures and components in their operational environment.
However, it’s important to note that MPI has limitations. It is primarily effective for ferromagnetic materials and is limited to detecting discontinuities near the surface. Additionally, it may not be suitable for components with complex geometries or irregular shapes.

Advantages

• Portable (on-site and in-house).
• Relatively simple method.
• Sensitive.
• Quick instant results.
• Sub-surface defects detection possible (approximately 1mm-2mm).

What defects/indications can it detect?

• Surface breaking defects.
• Toe cracks.
• Surface porosity.
• Crater cracks.

Commonly used to test

• Weldings.
• Castings.
• Shafts.

Limitations

• Uses a flammable liquid.
• Power may be needed.
• Temperature dependent.
• A clean surface is required before inspection.

Alternative inspection methods

• Dye Penetrant Inspection (DPI).
• Eddy Current Inspection (EC).

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