What does the term "magnetic saturation" refer to in MPT?

The term "magnetic saturation" in Magnetic Particle Testing (MPT) refers to a state where a ferromagnetic material has reached its maximum level of magnetization. At this point, any increase in the applied magnetic field will not result in any further magnetization of the material. This phenomenon is crucial in MPT because if a material is magnetically saturated, it can no longer effectively reveal surface or near-surface defects, as the magnetic field lines cannot be further concentrated around the areas of interest. Therefore, understanding magnetic saturation helps in ensuring that the magnetic field strength applied during testing is within an effective range to enhance the visibility of defects without reaching the saturation threshold. This understanding is fundamental for ensuring the reliability and accuracy of defect detection during the testing process.