What is the purpose of using an indicator fluid in wet MPI?

The purpose of using an indicator fluid in wet Magnetic Particle Inspection (MPI) is to enhance the visibility of the magnetic particles on the surface. The indicator fluid typically contains a dye or some form of coloring agent that allows the inspector to see the particles more clearly against the background of the test surface. When magnetic particles, which are usually very fine, are suspended in this fluid, the contrast between the particles and the background is improved, making it easier to detect discontinuities such as cracks or defects in the material being examined.

Choosing this option is essential for effective inspection, as the visibility of the magnetic particles directly influences the detection capability of the inspection process. Proper visibility enables inspectors to identify flaws accurately, ensuring parts meet safety and quality standards. The other options, while they touch on various aspects of the inspection process, do not directly capture the primary role of the indicator fluid in enhancing particle visibility, which is crucial for successful wet MPI.