Surface defects in ferromagnetic materials like iron and steel can be detected using non-destructive testing methods like magnetic particle inspection (MPI). Many industries like automobile, oil and gas, aerospace, and steel manufacturing often use MPI to check their components. Most types of castings, forgings and machined parts can be inspected using MPI. The wet fluorescent magnetic particle inspection method involves the use of particles having fluorescent properties to detect finer defects on surfaces. It is a special type of wet magnetic particle inspection and is used in more sensitive applications where the reliability of components is critical.
Wet Fluorescent Magnetic Particle Inspection
The process of wet fluorescent magnetic particle inspection is optimized for faster and more reliable inspections of components where even minor defects are critical. The clear, bright fluorescent particles used in this inspection method can stick to a wide variety of surfaces without clumping. This gives vividly evident indications of defects and anomalies, resulting in a much faster inspection process. The background fluorescence of the particles is very less, which makes them suitable for highly sensitive applications, such as in the aerospace and automobile industries. The wet fluorescent MPI method is a great choice to inspect machined or welded parts for inclusions, shrink cracks, flakes, tears, and seams. It uses an oil- or water-based suspension of the fluorescent magnetic particles that is sprayed or gently flooded onto the surface being tested. For best results, all surfaces to be tested should be cleaned for optimal testing conditions and to minimize the risk of contamination of the particle suspension. To ensure uniformity of application, the suspension must be properly mixed and continuously stirred.
Wet Magnetic Particle Inspection
In a magnetic particle inspection process, the magnetic particles can be applied dry or in the wet form. Dry particles are typically used for field inspections and are designed to withstand higher temperatures. The wet method uses a petroleum-based or water-based carrier to make a suspension for the particles and is known as the wet magnetic particle inspection process. Wet inspection is the better inspection method for highly sensitive applications. This is because the equipment used in the wet process can quickly create an even layer of particles over the part or surface being inspected. Moreover, as the wet magnetic particles are smaller in size (10µm and lesser), they have higher mobility and adherence to surfaces. This makes them more sensitive than dry particles for inspection of critical components. It is also easier to apply the wet magnetic solution to large surfaces. In addition, wet magnetic particles offer protection against corrosion and hydrogen embrittlement.
