How does Magnetic Particle Testing typically detect discontinuities?

Magnetic Particle Testing (MPT) detects discontinuities by utilizing magnetic particles that are applied to the surface of a ferromagnetic material. When the material is magnetized, any surface or near-surface defects, such as cracks or voids, will disrupt the magnetic field. At these discontinuities, magnetic particles will accumulate, creating a visible indication of the defect.

This method is effective because it is sensitive to very small surface flaws, making it a preferred choice in quality assurance processes for critical components. The magnetic particles can be applied dry or suspended in a liquid, and once they gather at the site of a discontinuity, they can create a pattern visible under ultraviolet light or with the naked eye, thus revealing the presence and location of defects reliably.

Visual inspection, color changes, and temperature variations do not provide the specific and targeted detection capabilities that magnetic particles offer. Other methods like visual inspection may miss subsurface flaws, while color changes could pertain to the material's inherent properties rather than an indicator of a defect. Temperature changes do not correlate directly with the existence of discontinuities in the way that magnetic particle accumulation does.