What type of defect is best identified using magnetic particle testing (MT) on a steel tower member?

Magnetic particle testing (MT) is best suited for identifying surface and near-surface discontinuities in ferromagnetic materials, such as steel. A discontinuity is any interruption in the typical structure of a material. Specifically, MT excels at detecting cracks, seams, laps, and inclusions that are open to or just beneath the surface of the steel member. The process involves magnetizing the steel component and then applying fine magnetic particles to the surface. If a discontinuity is present, it disrupts the magnetic field, causing the magnetic particles to concentrate along the edges of the defect, making it visually detectable. While MT can detect some subsurface defects, its effectiveness diminishes rapidly with depth. It is not generally suitable for detecting defects deep within the material or for assessing material thickness variations. Therefore, MT is primarily used to identify surface-breaking or very near-surface flaws that could compromise the structural integrity of the steel member.