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Corrosion Monitoring & Inspection Glossary - M
Magnetic Field Strength: The magnitude of the magnetic field produced by a magnet.
Magnetic Flux: A measure of the amount of magnetization carried by a material.
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.
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.
Magnetic Particle Inspection (MPI): A nondestructive examination technique for locating surface flaws in steel using fine magnetic particles and magnetic fields.
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.
Magnetic Saturation: The degree of magnetization at which a further increase in magnetic field strength produces a decrease in magnetic permeability of a material.
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.
Maximum Allowable Operating Pressure (MAOP): The maximum internal pressure legally permitted during the operation of a pipeline.
Maximum Operating Pressure (MOP): The maximum internal pressure that cannot normally exceed the maximum allowable operating pressure expected during the operation of a pipeline.
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 .
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.
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.
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).
Mill Scale: The oxide layer formed during hot fabrication or heat treatment of metals.
Monitoring: Measurements or periodic inspections made at selected locations along the pipeline.
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