Non-Destructive Testing (NDT) Practice Test

What phenomenon occurs when a part under inspection has a crack or disturbance to the lines of flux?

1. Magnetic field enhancement

2. Flux leakage field

3. Field saturation

4. Residual magnetism

The correct answer is: Flux leakage field

The phenomenon that occurs when a part under inspection has a crack or disturbance to the lines of flux is known as flux leakage field. This is fundamental to magnetic particle testing, a common non-destructive testing method. As the magnetic field is applied to the test material, it naturally flows through the material to create a magnetic circuit. When there are imperfections such as cracks, voids, or other discontinuities, these disturbances disrupt the normal flow of the magnetic field lines. As a result, some of the magnetic field lines "leak" from the intended path, concentrating at the area of the defect. This leakage creates a magnetic field outside the part that can be detected, usually by applying ferromagnetic particles that will accumulate at these locations, highlighting the defects. Understanding this principle is essential for effective assessment using magnetic particle testing, as the identification of these flux leakage fields indicates the presence of potential flaws in the material.