Non-Destructive Testing (NDT) Practice Test

How do magnetic particle indications form in the wet continuous method?

1. Through surface roughness of the test piece

2. From cracks created during initial magnetizing

3. Due to the prepared bath penetrating surface cracks

4. By external magnetic influences

The correct answer is: Due to the prepared bath penetrating surface cracks

In the wet continuous method of magnetic particle testing, indications are formed due to the presence of surface discontinuities, such as cracks. The testing involves the application of a magnetic field to the test piece, which can cause the magnetic lines of force to bend and concentrate at these discontinuities. When a prepared bath containing magnetic particles is applied, these particles are drawn to the areas of the magnetic field that are distorted by the surface cracks or other flaws. The key reason for the correct answer relates to how the prepared bath interacts with the test surface. The magnetic particles in the wet bath can effectively penetrate surface cracks and gather at these locations, creating visible indications of the flaws. This process relies on the magnetic attraction and movement of the particles to reveal issues that might not be visible to the naked eye. In this context, surface roughness may have an effect on the formation of indications, but it is not the primary reason for their formation. Similarly, external magnetic influences can impact the magnetic field but do not directly contribute to the formation of indications within the surface flaws. Cracks created during initial magnetizing is also not a correct approach to understanding the formation of indications, as the initial magnetizing is meant to identify existing flaws rather than create new ones.