Magnetic Particle Inspection

Magnetic particle inspection is a non-destructive surface inspection method that is used to detect cracks and other defects on surface and near-surface of ferromagnetic materials. Magnetic particle inspection can be performed using a wet or dry method, depending on the application.

• Wet method

The wet method uses the magnetic powder suspended in oil, water or other liquid medium and uniformly distributes the magnetic suspension on the surface of the workpiece in the detection process. The flow of carrier liquid and the attraction of magnetic powder by leakage magnetic field indicate the shape and size of the defect. In the wet detection, the magnetic powder particles that can be used are smaller because of the dispersion and suspension performance of the magnetic suspension. Therefore, it has high detection sensitivity.

• Dry method

Dry method directly applies the special dry magnetic powder to the magnetized workpiece according to the procedure, and the defects of the workpiece show magnetic marks. Dry inspection is ideal for local area inspection of large castings, forgings, large structures and weldments, and is usually used in conjunction with portable equipment.

Test Procedures

• Preparation before testing: Check the sensitivity of the testing equipment, remove the oil and rust on the surface of the tested parts.
• Magnetization.
• Apply magnetic powder or magnetic suspension.
• Observation and evaluation of magnetic marks.
• Demagnetization.
• Cleaning, drying, anti-rust.
• Record the results: Record the magnetization process, specimen status, magnetization current, magnetization mode, interpretation and evaluation of magnetic marks, test date, operator and evaluator, and final test results.

Test Capabilities

• Detect cracks with very narrow gaps or defects that are difficult to see with the naked eye on the surface and near-surface of ferromagnetic materials.
• Detect defects of Fe-Ni-based ferromagnetic materials, such as martensitic stainless steel and precipitation hardening stainless steel.
• Detect defects of unprocessed raw materials and processed semi-finished products, finished products, and in-service and used workpieces.
• Detect defects of pipes, bars, plates and shapes, forging steel castings and welding parts.
• Detect defects where the extension direction of the workpiece surface and near surface is perpendicular to the direction of the magnetic field line as much as possible.
• Detect small defects (not shallow and wide defects) on the surface and near surface of the workpiece.

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