Magnetic Particle Testing is a widespread and easy-to-use NDT technique. As its name applies, it works by having the tester create a magnetic field around the object being inspected. This is done with a permanent or electromagnet, induced magnetic field (such as a current-carrying coil) or a direct electrical current running through the object.
The object being tested is then coated with tiny iron particles. The current magnetizes the particles to the surface, revealing any flaws. While this might seem complicated, it is pretty simple and easy to use. It is fast, can be inexpensive, and many MPI instruments are portable.