Uses high-frequency sound waves to detect internal flaws or to measure thickness. A probe sends sound waves into the material, and any flaws reflect those waves back. The echoes are analyzed to locate and size defects like cracks, voids, or corrosion.

Uses X-rays or gamma rays to penetrate materials and capture an image on film or a digital detector. Internal defects such as voids, porosity, or cracks show up as dark spots on the radiograph.

Used on ferromagnetic materials. The part is magnetized, and fine magnetic particles are applied. If there is a surface or slightly subsurface defect, it disrupts the magnetic field and attracts the particles, creating a visible indication.

Used to detect surface-breaking defects. A dye or fluorescent liquid is applied to the surface, seeps into any cracks, and is then drawn out with a developer to reveal flaws under visible or UV light.

Uses electromagnetic induction to find surface and near-surface defects in conductive materials. A probe generates eddy currents in the material; flaws affect how those currents flow and are detected by changes in the probe's signal.