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After the ferromagnetic material and the workpiece are magnetized, due to the discontinuity, the magnetic field lines on the surface of the workpiece and the near surface are locally distorted to generate a floor magnetic field, and the magnetic powder applied on the surface of the workpiece is adsorbed to form a magnetic field visible under suitable illumination. Traces, showing the location, shape and size of the discontinuities. as the picture shows:

Applicability of magnetic particle testing Magnetic particle testing is suitable for detecting ferromagnetism when the surface and near surface are small in size and the gap is extremely narrow (for example, cracks with a length of 0.1 mm and a width of micron can be detected), and visual discontinuities are difficult to see.

Martensitic stainless steel and precipitation hardened stainless steel are magnetic and can be used for magnetic particle testing. Commonly used in weld quality inspection to detect weld surface and near surface defects.

Magnetic particle testing program
(1) Pretreatment
(2) Magnetization
(3) Applying magnetic powder or magnetic suspension
(4) Observation and recording of magnetic marks
(5) Defect rating
(6) Demagnetization
(7) Post-processing

Characteristics of magnetic particle testing
(1) Suitable for testing of ferromagnetic materials, not for being able to be used for non-ferromagnetic materials
(2) defects on the surface and near surface can be detected, and internal defects cannot be detected
(3) High sensitivity, fine cracks can be found
(4) The detection cost is very low and fast
(5) The shape and size of the workpiece sometimes affect the flaw detection, and it is difficult to magnetize and cannot be inspected.

Common portable magnetic particle flaw detector