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Definitions M-N

 

Macroscopic: View with little or no magnification. Usually photographs that are taken with a normal lens. Technically speaking, macro photography means shooting at a magnification ratio of at least 1:1. Therefore, a 'true' macro lens has the ability to produce a magnification ratio of 1:1, or higher. A more specific definition of a macro lens, is one whose minimal focus distance is short enough to allow photography of a focused subject in 1:1 magnification.

Magnetic Particle Examination: A low-cost non-destructive examination conducted on ferrous metals such as iron, nickel, or cobalt; which can detect discontinuities, fatigues or cracks when magnetized. The examination is performed by submerging the subject into solution and when the metal is magnetized using an external magnetic field, a flux leakage bridge will occur at cracks and flaws that egress the surface. Iron oxide particles broken loose from the solution will cluster at the flux leakage area(s), and can be easily detected using a form of ultraviolet illumination.

magnetic particle examination

Makeup: Oil field slang for separating joints that connect pipe sections or a drill collar together in a drill string.

Makeup Torque (ft. lb): Torque applied to tighten a nut onto a bolt or threaded fastener or into a threaded hole. Torque is applied to impart a certain predetermined clamping force to a joint.

Martensite: The micro structural arrangement in steel formed when austenite is quickly cooled. This phase or microstructure is unstable and will convert to a more stable structure when heated. Martensite is very hard but also very brittle. Tempering reduces hardness but increases toughness.

Match Mark: A fine line or circle drawn across a fracture, valve handle, or any subject piece of material used to denote the original position or location of the subjects moveable (or removable) parts prior to cutting, turning or any changes made to the original position.

Mechanical Damage: Damage or alteration of a component or fracture surface because of a force being applied with a tool or instrument. Mechanical damage can also occur on a fracture surface because of mutual contact of the fracture surfaces during the failure process or subsequent to the accident event.

Mechanical Property Determination: Metals and alloys have properties that are consistently exhibited by each metal or alloy. The common mechanical properties of interest to metallurgical engineers are yield strength, tensile strength, endurance limit, elongation, reduction of area, hardness, etc. These properties are determined by the certain distinct and standardized tests, which are conducted with specialized equipment in a testing laboratory.

Metal Fatigue: A mode or mechanism of failure during which the stress applied to the device is alternating with time and usually at a high frequency. A few common types of alternating stresses are: push-pull-push-pull, bending up, bending down (two way bending) and vibration. When metal fatigue occurs, a crack is initiated or started at a point of high stress and/or stress concentration. During any stress cycle where the tip of the crack is opened, the crack may grow or extend. Each time the crack grows, a striation or birthmark is left to attest to the fact that a crack has grown at that location by the mechanism of metal fatigue. Usually metal fatigue has a very distinctive macroscopic appearance. A SEM showing fatigue crack growth from lower left toward upper right at 10,000x is shown below.

SEM of fatigue crack growth
Scanning electron micrograph showing fatigue crack growth.

More cases involving Metal Fatigue:

Chemical Plant Accident

Articles about Metal Fatigue:

Taking the Mystery out of Metal Fatigue (Pt. 1)

Taking the Mystery out of Metal Fatigue (Pt. 2)

Taking the Mystery out of Metal Fatigue (Pt. 3)

Metal Inert Gas Welding (MIG): MIG welding is an arc-welding process, in which the heat from an electrical arc is used to melt the base and filler metals. In MIG welding, a continuous wire is used as filler metal. The filler metal is fed from the welding gun and melted into the weld puddle. This wire also serves as the electrode for the electrical arc. Along with the wire, a gas also flows out of the welding gun around the wire electrode. This gas, which is normally carbon dioxide or a mixture of carbon dioxide and argon, creates a non-reactive atmosphere that protects the pool of molten metal at the weld site from the atmosphere. Molten metal is extremely reactive to gases such as oxygen and hydrogen in the air, and these reactions are detrimental to weld integrity. In addition to the protection offered by the inert gas shielding, the welding wire has a small core of flux. In MIG welding, this flux acts in two ways. It typically contains deoxidizers that help reverse any oxidation that may take place in the weld pool and also adds another layer of protection from the atmosphere by either forming a protective slag or by disintegrating into additional protective gas at welding temperatures. The amount of slag formed in MIG welding is much lower than most other welding processes.

Metallography: A metallurgical testing process that with the aid of a metallurgical microscope, allows the observer to examine the internal structure of a piece of metal. The internal structure will reveal the microstructure (how the metal grains are arranged and their size), impurities (such as non-metallic inclusions), crack development, progression, the existence of cold work and grain boundary precipitates. A sample of the metal of interest is cut, encased in plastic (mounted, but sometimes a metallographic examination is performed without mounting), and the cut metal surface is polished to a mirror finish and often examined in that condition. Additional micro structural details are revealed by etching (usually by dipping or swabbing the polished surface with a dilute acid etchant) to reveal the metal microstructure.

Metallurgical Engineer: A person who can diagnose an accident or failure of a metal component, whether it is a simple consumer product such as a hammer or chisel, or a complex multi-component machine such as an airplane or a space shuttle. Failures are normally complex where often two, three or more separate but necessary circumstances or events are required to simultaneously or sequentially occur to cause the failure or accident. A metallurgical engineer’s analysis of a metal failure may include many of the following: scene/site examination and documentation, evidence preservation, standards and literature review, visual examination, macroscopic examination or microscopic photography, laboratory testing, engineering calculations, data and file analysis and report preparation.

Metallurgical Failure Analysis: Metallurgical Failure Analysis is a scientific process in which a cracked or fractured piece of equipment or weld is analyzed to determine the cause of failure. Metallurgical failure analysis begins with visual examination, photo-documentation and microscopic examination. This non-destructive phase of examination may be followed by laboratory testing. The laboratory phase of metallurgical failure analysis involves cutting samples from fractured or cracked items, conducting a microscopic examination of the fracture or crack, cutting, mounting and polishing samples for scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro structural examination, micro hardness testing and profiling, chemical analysis, etc. The goal of the process is usually to ascertain why the component cracked or fractured, i.e., causation of the crack or failure.

Metallurgy: The science that deals with procedures and processes used in extracting metals from their ores, purifying and alloying metals, and creating useful objects from metals. Metallurgy is the study of metals, their properties and processes that can be used to change/alter metal properties in bulk and at the atomic level.

Microstructure: The microstructure of a metal is the internal structure of the metal. A metal is made up of different grains (like grains of sand, which are firmly stuck together) and phases (like chocolate chips or nuts in a cookie). This internal microstructure is related to the chemistry or chemical elements that are in the metal and many other factors such as rolling, forming, heat treatment, etc. that occur during fabrication of the object in question. To examine the microstructure, the metal object is cut and the cut surface is polished and etched with dilute acid. This process reveals the microstructure, which is then viewed with a microscope at various levels of magnification.

Mooring Line: A cable, wire rope or line that holds an object, especially a vessel/barge in place.

Necking: During the application of high tensile or stretching forces, metals begin to flow or stretch permanently for example, plastic or permanent deformation. This plastic/permanent deformation occurs in localized areas where the metal thins before fracturing.

Nichrome: is a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire such as a heating filament. These alloys typically contain 60-80% nickel and are resistant to high temperature oxidation.

Nital Etchant: A 2-5% diluted mixture of nitric acid in alcohol. Etching is used to reveal the internal microstructure of the metal.

Non-Destructive Testing: Testing which does not destroy or physically change the configuration of the object to be tested. Examples are visual examination, magnetic particle inspection, dye penetrate inspection, x-radiation, etc.

Non-metallic Inclusions: Compounds which consist of one or more metals, i.e., copper (Cu), manganese (Mn), iron (Fe), etc. and one or more nonmetals, i.e., sulfur, (S), oxygen (O), silicon (Si), etc. During the forming and processing of steel, non-metallic inclusions in the form of oxides and sulfides are rolled or formed into the metal. When steel is rolled or fabricated into a sheet the non-metallic inclusions are aligned and often are elongated in the direction of rolling.

Nozzle: A mechanical device that controls the direction of a fluid or gas flow.

Normalized: A microstructure formed in steel when it is allowed to slowly cool from the Austenite phase.

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