Principle: After ferromagnetic materials and workpieces are magnetized, due to the presence of discontinuities, the magnetic field lines on the surface and near the surface of the workpieces undergo local distortion, resulting in leakage magnetic fields. Magnetic particles applied to the surface of the workpieces are adsorbed, forming visible magnetic marks under appropriate lighting, thereby displaying the location, shape, and size of the discontinuities.
Applicability and limitations:
Magnetic particle inspection is suitable for detecting discontinuities on the surface and near surface of ferromagnetic materials that are very small and have extremely narrow gaps (such as cracks that can be detected in the length of 0.1mm and width of micrometers) that are difficult to detect visually; It can also inspect raw materials, semi-finished products, finished workpieces, and in-service components, as well as plates, profiles, pipes, bars, welded parts, cast steel parts, and forged steel parts. Defects such as cracks, inclusions, hairlines, white spots, folds, cold shuts, and looseness can be found.
However, magnetic particle testing cannot detect austenitic stainless steel materials and welds welded with austenitic stainless steel electrodes, nor can it detect non magnetic materials such as copper, aluminum, magnesium, titanium, etc. It is difficult to detect shallow scratches, deep buried holes, and delamination and folding with an angle less than 20 ° from the workpiece surface.
Penetrant Testing (PT)
Principle: After the surface of the part is coated with a penetrant containing fluorescent or coloring dyes, under the action of a capillary tube, after a period of time, the penetrant can penetrate into the surface opening defects; After removing the excess penetrant on the surface of the part, a developer is applied to the surface of the part. Similarly, under the action of a capillary, the developer will attract the retained penetrant in the defect, and the penetrant will seep back into the developer. Under a certain light source (ultraviolet or white light), the traces of the penetrant at the defect are realized (yellow green fluorescence or bright red), thereby detecting the morphology and distribution status of the defect.
Advantages and limitations:
Penetrant testing can detect various materials, including metallic and non-metallic materials; Magnetic and non magnetic materials; Welding, forging, rolling and other processing methods; Has high sensitivity (can be found to be 0.1 μ M wide defect, with intuitive display, convenient operation, and low detection cost.
But it can only detect defects with surface openings and is not suitable for inspecting workpieces made of porous and loose materials and workpieces with rough surfaces; Only the surface distribution of defects can be detected, making it difficult to determine the actual depth of defects, making it difficult to quantitatively evaluate defects. The detection results are also greatly influenced by the operator.
Email: oiltools14@welongpost.com
Grace Ma
Post time: Nov-14-2023
