What are the different grades of magnetic particles according to ASNT?

In the context of magnetic particle testing, the grading of magnetic particles according to ASNT is based on their particle size and suitability for detecting different types of discontinuities in ferromagnetic materials.

The correct grading is broken down as follows: Grade A is classified as ultra-fine particles, which are capable of revealing very subtle surface defects due to their small size. Grade B consists of fine particles, which are also effective for detecting small defects but to a slightly lesser degree than ultra-fine particles. Grade C, categorized as medium particles, offers a balance between sensitivity and coverage, suitable for general applications. Finally, Grade D is classified as coarse particles, which are typically used for detecting larger defects but are less sensitive to smaller discontinuities.

This hierarchy of particle size is designed to provide flexibility in testing applications, enabling inspectors to select the appropriate grade based on the expected size and nature of the discontinuities being examined. The smaller the particle, the greater the ability to detect finer defects, making the understanding of these grades essential for effective quality control in various industrial processes.