MT is effective for detecting surface and near surface discontinuities in ferromagnetic materials such as steel, iron, nickel, cobalt, and some of their alloys. The process is achieved by inducing a magnetic field into the test specimen through the use of an electromagnet or permanent magnet. When magnetized, flaws perpendicular to the magnetic field direction will result in flux leakage. Ferromagnetic particles are flowed across the test surface and if a discontinuity exists, the particles will be attracted to the flawed area producing an “indication”. The indication can then be evaluated against applicable acceptance criteria.
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