Corrosion Glossary - M

Macrohardness: the hardness of a coating as measured on a macroscopic scale, which shows the coatings bulk properties.
Magnetron sputtering: in this PVD process, the sputtering action is enhanced by intense magnetic fields.
M alkalinity: Methyl orange alkalinity. (See total alkalinity.)
MAG: metal active gas welding process usingcarbon dioxide (CO₂) and argon (CO₂) mixtures.
Magnetic Particle Examination (MT): a method of detecting cracks at or near the surface in magnetic alloys.
Make-up: the water added to boiler feed to compensate for that lost through exhaust, blowdown, leakage, etc.
Manganese greensand: greensand which has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water.
Manganese zeolite: synthetic gel zeolite which has been processed in the same manner as manganese greensand, and used for similar purposes.
Manhole: the opening in a pressure vessel of sufficient size to permit a man to enter.
Manifold: a pipe or header for collection of a fluid from, or the distribution of a fluid to a number of pipes or tubes.
Material Safety Data Sheet (MSDS): information sheet that lists any hazardous substance that comprises one percent or more of the product's total volume. Also lists procedures to follow in the event of fire, explosion, leak or exposure to hazardous substance by inhalation, ingestion or contact with skin or eyes. Coatings manufacturers are required to provide retailers with an MSDS for every product they sell to the retailer. Sales clerks should make MSDS available to retail customers.
Matrix: the continuous phase of a material or coating in which separate particles of another constituent are embedded. An example is tungsten carbide particles embedded in a cobalt matrix.
Maximum allowable working pressure: the maximum gauge pressure permissible in a completed boiler. This pressure is based upon either proof tests or calculations for every pressure part of a vessel using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the vessel.
Maximum continuous load: the maximum load which can be maintained for a specified period.
Maximum contaminant level (MCL): the maximum allowable concentration of a contaminant in water as established in the U.S. EPA Drinking Water Regulations.
Mechanical bonding: usually represented by mechanical interlocking of the deposited particles with the rough heights on the substrate surface produced during grit blasting.
Mechanical filter: a filter primarily designed for the removal of suspended solid particles, as opposed to filters with additional capabilities.
Media: the plural form of "medium".
Medium: a material used in a filter bed to form a barrier to the passage of certain suspended solids or dissolved molecules.
Mesa corrosion: mesa corrosion is one of the common types of corrosion experienced in service involving exposure of carbon or low alloy steels to flowing wet carbon dioxide conditions at slightly elevated temperatures. An iron carbonate surface scale will often form in this type of environment which can be protective rendering a very low corrosion. However, under the surface shear forces produced by flowing media, this scale can become damaged in a localized attack produces mesa-like features.
Metal dusting: accelerated deterioration of metals in carbonaceous gases at elevated temperatures to forrn a dust-like corrosion product.
Metallizing: See thermal spraying.
Metallurgical bonding: produced by diffusion or chemical bonding between the coating and substrate.
Methylene Blue Active Substances: chemical compounds which react with methylene blue to form a blue compound which can be used to estimate the concentration by measurement of the depth of color. Substances measured include ABS and LAS types of detergents, thus the term is commonly used as an expression of detergent concentration.
Microbiologically Influenced Corrosion: sometimes called Microbial Corrosion or Bio corrosion refers to corrosion that is affected by the action of microorganisms in the environment.
Micrograph: a micrograph is produced when a section of the coating is taken, polished to show the particulate layers and then photographed through a microscope.
Microhardness: the hardness of a coating as measured on a microscopic scale. Can show the hardness of individual phases within the coating and avoid the effects of porosity.
Micrometer (µm): formally known as micron. A linear measure equal to one millionth of a meter or .00003937 inch. The symbol for the micrometer is µm.
Micron: See micrometer.
Microstructure: the structure of a prepared surface of a metal as revealed by a microscope at a magnification exceeding 25x.
MIG: the metal inert gas (argon or other) welding process.
Mil: One thousandth of an inch.
Mill scale: the heavy oxide layer formed during hot fabrication or heat treatment of metals.
Mineral: a term applied to inorganic substances such as rocks and similar matter found in the earth strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure.
Mineral acidity: Acidity due to the presence of inorganic acids such hydrochloric, sulfuric and nitric acids, as opposed to acidity due to carbonic acid or organic acids.
Mineral spirits: paint thinner. Solvent distilled from petroleum.
Mixed potential: the potential of a specimen (or specimens in a galvanic couple) when two or more electrochemical reactions are occurring simultaneously.
MMA: the manual metal arc welding process.
Moisture: water in the liquid or vapor phase.
Moisture in steam: particles of water carried in steam, expressed as the percentage by weight.
Moisture loss: the boiler flue gas loss representing the difference in the heat content of the moisture in the exit gases and that at the temperature of the ambient air.
Molal solution: concentration of a solution expressed in moles of solute divided by 1000 g or 1 kg of solvent
Molar solution: aqueous solution that contains 1 mole (gram-molecular weight) of solute in 1 liter of the solution.
Mole: one mole is the mass numerically equal (in grams) to the relative molecular mass of a substance. It is the amount of substance of a system that contains as many elementary units (6.023 10^23) as there are atoms of carbon in 0.012 kg of the pure nuclide C12.
Molecule: the simplest combination of atoms that will form a specific chemical compound; the smallest particle of a substance which will still retain the essential composition and properties of that substance, and which can be broken down only into atoms and simpler substances.
Moneypenny-Strauss test: corrosion testing in a copper-sulfate solution containing sulfuric acid. used to detect the susceptibility of stainless steel to intergranular corrosion.
Monomer: a molecule usually an organic compound, having the ability to join with a number of identical molecules to form a polymer.
Most probable number (MPN): the term used to indicate the number of microorganisms which, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests; usually expressed as a number per 100 ml of water.
Mottle: (coating) a term often used interchangeably with flooding or floating.
MPN: the abbreviation for "most probable number".
Muriatic acid: archaic term for hydrochloric acid, HCl (acidum salis, marine acid, spirit of salt).

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