What is the role of the magnetic field in magnetic particle testing?

The role of the magnetic field in magnetic particle testing is essential for detecting surface variations in ferromagnetic materials. When the magnetic field is applied, it magnetizes the object being tested, causing the magnetic particles that are spread over its surface to gather at any discontinuities or defects that disrupt the magnetic field. These discontinuities can be cracks, laps, or inclusions. The accumulation of magnetic particles at these areas makes them visible, thereby enabling inspectors to easily identify flaws that could compromise the integrity of the material.

By creating a magnetic field, the test ensures that any surface discontinuity effectively traps the magnetic particles, highlighting defects that might otherwise go unnoticed. This capability is what makes magnetic particle testing a preferred method for non-destructive testing of materials in critical applications, ensuring that they meet safety and quality standards.