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.

A crack that nucleates at the center of a saw blade can be detected using dry magnetic particle testing.
Indication of a Crack in a Saw Blade
Cracks that develop along weldments can be detected using magnetic particle inspection.
Indication of Cracks in a Weldment
Stress concentrations at fastener hols can cause cracks that connect from one hole to another. Dry magnetic particle can detect these cracks.
Indication of cracks Originating at Fastener Hole

A crack eminating from a hole may be so thin that it is difficult to detect with the unaided eye.  Magnetic particle testing makes cracks more visible.

Before and After Inspection Pictures of Cracks Emanating From a Hole

Stress concentrations at fastener hols can cause cracks that connect from one hole to another. Dry magnetic particle can detect these cracks.
Indication of Cracks Running Between Attachment Holes in a Hinge