Magnetic Particle Inspection Level 1 Practice Exam

What happens to ferrous materials when the magnetizing current stops flowing?

1. They lose all magnetism

2. They retain residual magnetism

3. They become demagnetized

4. They magnetize in the opposite direction

The correct answer is: They retain residual magnetism

When the magnetizing current stops flowing in ferrous materials, they retain residual magnetism. This phenomenon occurs because while magnetic domains within the material become aligned with the external magnetic field during magnetization, once the magnetizing field is removed, some of these domains remain aligned in the direction of the previous field. The degree to which a ferrous material retains its magnetism after the magnetizing current ceases can vary based on the type of material and its treatment. Some materials, such as soft iron, will lose most of their magnetism quickly after the field is removed, while others, like hard steel, will maintain significant residual magnetism due to their magnetic properties. This retention of magnetism is crucial in magnetic particle inspection, as it allows for the identification of surface and subsurface discontinuities in materials through the use of magnetic particles, which cling to the magnetic field created by these residual magnetism areas. Understanding this concept is essential for performing effective inspections.