In magnetic particle inspection, what is a key rule regarding the depth and width of surface discontinuities?

In magnetic particle inspection, the relationship between the depth and width of surface discontinuities plays a critical role in detecting defects effectively. A key rule is that the depth of the defect should be at least five times the width of the opening. This guideline stems from the way magnetic particle inspection works—where the magnetic field must be able to penetrate adequately through the material to reveal the discontinuity.

If the depth of the discontinuity is not sufficient compared to its width, there is a risk that the magnetic field will not be disturbed enough to indicate the presence of the defect. The greater the depth as related to the width, the more pronounced the magnetic field distortion will be, allowing for a more reliable indication when magnetic particles are applied.

This rule helps ensure that the notification of a defect is both accurate and reliable, thus enhancing the quality and safety of the material being inspected. By adhering to this relationship, inspectors can maximize the effectiveness of the magnetic particle inspection process.