Magnetic particle testing

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Material type: Suitable for detecting ferromagnetic materials based on iron and nickel, such as martensitic stainless steels and precipitation-hardening stainless steels. It is effective for detecting surface and near-surface defects in ferromagnetic materials; for example, it can detect cracks and minor defects caused by casting, quenching, machining, fatigue, and other factors. It is not suitable for detecting non-magnetic materials, such as austenitic stainless steel, copper, aluminum, and other non-ferrous metal materials. Workpiece status: Suitable for detecting raw materials that have not been processed (such as steel billets), as well as processed semi-finished products, finished parts, and workpieces that are in use or have already been used. It can be used to inspect various components, such as crankshafts, camshafts, spline shafts, and other small to medium-sized parts. It is suitable for detecting workpieces of various shapes, including pipes, bars, sheets, profiles, forged steel parts, cast steel parts, and welded parts. Defect orientation: It is suitable for detecting defects on the surface of workpieces or near their surface whose extension direction is as perpendicular as possible to the direction of the magnetic field lines; however, it is less effective for detecting defects whose extension direction forms an angle of less than 20 degrees with the direction of the magnetic field lines. Advantages of magnetic particle testing: High detection sensitivity: It can accurately detect cracks at the micron level, as well as very small surface and near-surface defects; it exhibits high sensitivity in detecting such defects on the surface and near the surface of ferromagnetic materials. The results are intuitive and accurate: it can clearly and precisely display the location, shape, and size of defects, and to a certain extent determine the nature of those defects, facilitating judgment and analysis by inspectors. Easy to operate: The operation is relatively simple; no complex equipment or skills are required, making it convenient for flaw detection on large equipment and workpieces on-site. Lower cost: Compared to some other non-destructive testing methods, the equipment and materials required for magnetic particle testing are relatively inexpensive, resulting in lower testing costs as well. Environmental protection: To a certain extent, it can reduce damage to the ecological environment, as well as save energy and materials. High versatility: It is hardly affected by the size and geometry of the workpiece, allowing for the inspection of workpieces of various shapes and sizes. Disadvantages of magnetic particle testing: Limited detection range – it can only detect surface and near-surface defects in ferromagnetic materials; it is unable to detect deeper internal defects or issues such as layering within the material, and it is difficult to determine the depth of defects. High surface requirements: High smoothness is required of the surface of the part being inspected; otherwise, it will affect the adhesion of magnetic powder and the accuracy of the inspection results. If the workpiece surface contains impurities such as rust, oil, dust, etc., pre-treatment is required. High technical requirements: The test results are greatly influenced by the skills and experience of the testers; professional testers are needed to carry out the tests and make judgments in order to ensure the reliability of the results. Magnetic flaw analysis is complex: sometimes unrelated magnetic flaws appear, requiring inspectors to conduct accurate analysis and judgment in order to distinguish between real defects and false ones, which increases the difficulty and complexity of the inspection. There is some level of contamination: the magnetic powder and magnetic suspension used may cause certain contamination on the surface of the workpiece, requiring subsequent cleaning. Not applicable to some workpieces: For components with high surface quality requirements, such as those with precisely machined surfaces, the contact method and direct current application used in magnetic particle testing may generate arcs that can burn the components, hence they are not suitable for this method.