What are the two main methods of applying magnetic fields in MPT?

Magnetic Particle Testing (MPT) relies on the application of magnetic fields to detect surface and near-surface defects in ferromagnetic materials. The two primary methods of applying these magnetic fields during the testing process are categorized as direct and indirect methods.

In the direct method, magnetic lines of force are produced in the test object itself by passing electric current through it. This method allows for the detection of defects that are aligned with the magnetic field, as the magnetic particles will accumulate at areas of flux leakage, indicating potential flaws.

On the other hand, the indirect method involves generating a magnetic field around the test object, typically using a coil or other external source. This method enables inspection without needing to pass current directly through the component, which can be advantageous for certain geometries and sizes of materials.

Understanding these fundamental methods provides the basis for selecting the appropriate technique based on the specific requirements of the inspection process and the characteristics of the material being tested.