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Introduction to Magnetic Particle Inspection

Introduction
Introduction
Basic Principles
History of MPI

Physics
Magnetism
Magnetic
Mat'ls
Magnetic Domains
Magnetic Fields
Electromag. Fields
Field From a Coil
Mag Properties
Hysteresis Loop
Permeability
Field Orientation
Magnetization of Mat'ls
Magnetizing Current
Longitudinal Mag Fields
Circular Mag Fields
Demagnetization
Measuring Mag Fields

Equipment & Materials
Portable Equipment
Stationary Equipment
Multidirectional Equipment
Lights
Field Strength Indicators
Magnetic Particles
Suspension Liquids

Testing Practices
Dry Particles
Wet Suspension
Magnetic Rubber
Continuous & Residual Mag
Field Direction & Intensity
L/D Ratio

Process Control
Particle Concentration
Suspension Contamination
Electrical System
Lighting
Eye Considerations

Example Indications
Visible Dry Powder
Fluorescent Wet

Quizzes

Examples of Visible Dry
Magnetic Particle Indications

One of the advantages that a magnetic particle inspection has over some of the other nondestructive evaluation methods is that flaw indications generally resemble the actual flaw. This is not the case with NDT methods such as ultrasonic and eddy current inspection, where an electronic signal must be interpreted. When magnetic particle inspection is used, cracks on the surface of the part appear as sharp lines that follow the path of the crack. Flaws that exist below the surface of the part are less defined and more difficult to detect. Below are some examples of magnetic particle indications produced using dry particles.


Indication of a crack in a saw blade


Indication of cracks in a weldment


Indication of cracks originating at a fastener hole

 
Before and after inspection pictures of cracks emanating from a hole


Indication of cracks running between attachment holes in a hinge