Magnetic Particle Examination (MT)
MT can be used to detect surface and near surface flaws in ferromagnetic materials. MT cannot be used for austenitic stainless steel pressure vessels, because these materials cannot be magnetized.
MT’s applicability to inspection of pressure vessels is similar to PT, mainly in that it is most useful for the detection of surface flaws, but MT is generally considered to give greater sensitivity for the detection of fine cracks. It is somewhat more difficult to apply than PT, and it requires considerably more investment in equipment.
Article 7 of ASME Code, Section V, gives the minimum requirements for an MT procedure for pressure vessels, and refers to ASTM Standard SE709 for additional details that should be considered when establishing an MT procedure.
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