Magnetic Particle Inspection

Non-destructive testing for ferromagnetic components. MPI detects surface and near-surface defects — cracks, seams, inclusions, and stress fractures — using magnetic field leakage and particle indication, with real-time visual results.

AC & DC

Magnetization Methods

Surface+

Near-Surface Detection

NDT

Non-Destructive Testing

Technology Overview

Non-Destructive Defect Detection

Magnetic Particle Inspection (MPI) is an established non-destructive testing (NDT) method used to detect discontinuities in ferromagnetic materials. Unlike destructive testing, MPI reveals surface cracks, seams, inclusions, laps, and stress fractures without altering the component — allowing 100% inspection of safety-critical parts prior to coating, assembly, or deployment.

Calico offers both AC (alternating current) and DC (direct current) magnetization methods. AC is preferred for surface crack detection and is effective even through thin non-ferrous plating. DC penetrates deeper into the material and is used for near-surface defect detection. Inspection is performed under standard white light or UV (black light) for fluorescent wet particle methods, enabling detection of extremely fine discontinuities.

Surface Detection Method

Near-Surface Method

Fluorescent Inspection

100%

Inspection Coverage

Process Overview

Precision at Every Step

Step 01

Magnetization

The component is magnetized using AC or DC current, selected based on defect type, depth, and geometry. Circular and longitudinal fields are applied sequentially to detect defects in all orientations.

Step 02

Particle Application

Ferromagnetic particles are applied to the magnetized surface — either as dry powder or as fluorescent particles suspended in carrier fluid — while the magnetic field is active to maximize particle mobility.

Step 03

Defect Indication

Magnetic field leakage at surface and near-surface discontinuities attracts and holds ferromagnetic particles. Accumulated particle clusters form visible indications that reveal defect location, shape, and orientation.

Step 04

Visual Inspection

Trained inspectors evaluate particle indications under standard white light or UV illumination. Results are documented and parts are disposition — accept, reject, or further evaluation — with full traceability.

Why MPI

Advantages of Magnetic Particle Inspection

Fast & High Sensitivity

MPI detects extremely fine surface discontinuities — down to fractions of a millimeter — and processes results in real time. Large batches of components can be inspected rapidly without per-part setup complexity.

Non-Destructive Testing

100% of safety-critical components can be tested without alteration, damage, or removal from service. Parts that pass inspection proceed directly to coating or assembly with full quality confidence.

Surface & Sub-Surface Detection

Both AC (surface) and DC (near-surface) magnetization methods are employed, ensuring detection of defects from the outermost surface layer through to sub-surface discontinuities in a single inspection cycle.

Real-Time Results

Particle indications are visible immediately during inspection — no film development, no scanning, no post-process analysis required. Inspectors evaluate and disposition parts on the spot with full traceability documentation.

Inspection Methods

MPI Process Options

Method	Current Type	Particle Type	Detection Depth
Wet Fluorescent (AC)	Alternating Current	Fluorescent Liquid Suspension	Surface discontinuities
Wet Fluorescent (DC)	Direct Current	Fluorescent Liquid Suspension	Surface + near-surface
Dry Powder (AC)	Alternating Current	Dry Ferromagnetic Powder	Surface discontinuities
Dry Powder (DC)	Direct Current	Dry Ferromagnetic Powder	Surface + near-surface

* MPI is applicable to ferromagnetic materials only (steel, iron, nickel alloys). For non-ferromagnetic materials, contact our applications team for alternative NDT methods including liquid penetrant inspection.

Ready to Engineer Your Advantage?

Talk to our applications team about integrating MPI into your quality process — before coating, before assembly, or as a standalone inspection service.

Tech Line: 704.483.2202

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