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Magnetic Field Strength:
The magnitude of the magnetic field produced by a magnet.
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Magnetic Flux: A measure
of the amount of magnetization carried by a material.
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Magnetic Flux Leakage (MFL):
The flows of flux from a magnetized material, such as the wall of a pipe,
into a medium with lower permeability, such as gas or air.
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Magnetic Flux Lines: A
representation of the strength and direction of a magnetic field. Flux lines
are drawn parallel to the direction of magnetic force. The spacing of these
lines represents the magnetic field strength. Flux lines always form nonintersecting
closed loops starting at the north pole and ending at the south pole of a magnet.
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Magnetic Particle Inspection (MPI):
A nondestructive examination technique for locating surface flaws in steel
using fine magnetic particles and magnetic fields.
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Magnetic Permeability:
The ability of magnetic flux to diffuse through (or permeate) a magnetic material.
The ratio of magnetic flux density to magnetic field strength.
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Magnetic Saturation: The
degree of magnetization at which a further increase in magnetic field strength
produces a decrease in magnetic permeability of a material.
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Mapping Pig: A configuration
pig that uses inertial sensing or some other technology to collect data that
can be analyzed to produce an elevation and plan view of the pipeline route.
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Maximum Allowable Operating Pressure
(MAOP): The maximum internal pressure legally permitted during the
operation of a pipeline.
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Maximum Operating Pressure (MOP):
The maximum internal pressure that cannot normally exceed the maximum allowable
operating pressure expected during the operation of a pipeline.
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Mechanical Damage: Any
of a number of types of anomalies in pipe caused by the application of an external
force. Can include dents, gouges, and metal loss .
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Mechanical Distortion:
Changes in wall thickness or changes in the cylindrical shape of a pipe.
A gouge, because it includes cold working, residual stresses, plastic strains,
and moved or removed metal, contains both mechanical and magnetic distortion.
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Metal Loss: Any of a number
of types of anomalies in pipe in which metal has been removed from the pipe
surface, usually due to corrosion or gouging.
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Microstructure: Structure
of metals and alloys as revealed after polishing and etching; hot-rolled steels
usually consist of bands of ferrite (iron) and pearlite (carbon) but may contain
other microstructures such as martensite (hard brittle grains) or bainite (not
as hard or brittle as martensite).
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Mill Scale: The oxide
layer formed during hot fabrication or heat treatment of metals.
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Monitoring: Measurements
or periodic inspections made at selected locations along the pipeline.
