T.O. 33B-1-1
Glossary 52
MACROPOROSITY (PT): Voids or gas pockets in metals that are large enough to be seen at magnification of less than
10 diameters.
MACROSCOPIC: Visible at magnifications from one to ten diameters.
MACROSCOPIC STRESSES: Residual stresses which vary from tension to compression in a distance (presumably
many times the grain size) which is comparable to the gage length in ordinary strain measurements, hence, detectable
by X-ray or dissection methods.
MACROSTRUCTURES: The structure of metals, as revealed by the eye or at a magnification of less than 10 diameters.
MAGNET: Materials that show the power to attract iron and other substances to themselves, and that exhibit polarity,
are called magnets.
MAGNET, PERMANENT: A highly retentive metal that has been strongly magnetized; for example, the alloy Alnico.
MAGNETIC COUPLING (MT): A term designating the interaction of a magnetic field with an adjoining test part.
MAGNETIC DISCONTINUITY (MT): This refers to a break in the magnetic uniformity of the part - a sudden change
in permeability. A magnetic discontinuity may not be related to any actual physical break in the metal, but it may
produce a magnetic particle indication.
MAGNETIC FIELD (MT): The space around a source of magnetic flux in which the effects of magnetism can be
determined.
MAGNETIC FIELD STRENGTH (MT): The intensity of the magnetic field surrounding the magnetized part measured
in GAUSS.
MAGNETIC FLUX: The total number of magnetic lines existing in a magnetic circuit is called “magnetic flux.”
MAGNETIC FORCE: In magnetic particle inspection the magnetizing force is considered to be the total force tending
to set up a flux in a magnetic circuit. It is usually designated by letter “H.”
MAGNETIC HYSTERESIS: See HYSTERESIS.
MAGNETIC LOOP: If a conductor carrying an electric current is bent in a loop, the magnetic lines of force enter on
one side of the loop and leave at the other, and the space within the loop is found to contain a magnetic field which has
very definite directional properties. Polarity is created within the coil with one end being a north pole and the opposite
end a south pole. The space enclosed by the loop is longitudinally magnetized.
MAGNETIC MATERIALS: Materials are affected by magnets in two general ways. Some of them are attracted by a
magnetic force, while others exert a repellent force. The first is called “paramagnetic” and the latter “diamagnetic.” In
magnetic particle inspection we are not ordinarily concerned with either of the two classes, but with what may be
termed a subdivision of the first class called “ferromagnetic materials.”
MAGNETIC PARTICLE INSPECTION (MT): A method for detecting discontinuities on or near the surface in suitably
magnetized materials, which employ finely divided magnetic particles that tend to congregate in regions of the
magnetic non-uniformity, i.e., along cracks, over inclusions, voids, etc.
MAGNETIC PERMEABILITY (MT): A term indicating the ease with which a magnetic field can be established in a
material. It is determined by the ratio of the strength of the resultant magnetic force to the applied magnetic force.
MAGNETIC POLES: The ability of a magnet to attract or repel is not uniform over its surface, but is concentrated at
local areas called “poles.” Each magnet has at least two poles, one of which is attracted by the earth’s North Pole and is
