Glossary of Terms

Home > Tools > Glossary of Terms

Instructions:Click on alphabet letter to jump down to those definitions.

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z


ABSOLUTE PRESSURE (psia): The total force per unit area exerted by a fluid. The sum of atmospheric and gage pressures.

ACCURACY: The degree to which an observed value matches the actual value of a measurement over a specified range.

ACID ETCH TEST. The application of a suitable acid to a metal surface for the purpose of determining the existence of surface imperfections, non-metallic inclusions, grain flow, grain size, and chemical segregation. 

ALLOWABLE STRESS. A percentage of minimum yield stress taking into consideration suitable safety factors. 

ALLOY STEEL: A Steel which owes its distinctive properties to elements other than carbon.

ALLOYING ELEMENTS. Elements which when added to steel and other primary metals in controlled amounts improve the properties of these materials. 

ALPHA IRON. The solid crystalline form of iron that is stable and exists below 1670 F. It is characterized by a body-centered cubic structure. 

ALTERNATING CURRENT (AC). Current that reverses polarity at a uniform frequency.

ALUMINUM. A metallic element approximately 65% lighter in weight than iron. It is used as a structural material when alloyed with other elements, or used as a deoxidizer and grain refiner in steels. 

ANNEALING. A softening treatment consisting of heating carbon or alloy steel to an appropriate temperature, holding at the temperature for a proper period of time and slowly cooling to room temperature. Austenitic stainless steels and nonferrous alloys are water quenched. 

ANSI. The American National Standards Institute is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.

AREA OF A CIRCLE: The measurement of the surface within a circle. To find the area of a circle, multiply the product of the radius times the radius by Pi (3.142). Commonly written  A=πr^2

ASME. ASME stands for the American Society of Mechanical Engineers. 

ASTM. ASTM stands for the American Society for Testing and Materials. 

ATMOSPHERIC PRESSURE. The force exerted per unit area by the weight of the atmosphere.

AUSFERRITE. A cast iron matrix microstructure, produced by a controlled thermal process, which consists of predominately acicular ferrite and high carbon austenite. See Austempered Ductile Iron. 

AUSTEMPERED DUCTILE IRON. A ductile cast iron that has been produced by a controlled thermal process which results in a matrix microstructure consisting of mainly acicular ferrite and high carbon austenite. 

AUSTENITE. A solid solution in which gamma iron (face centered crystal structure) is the solvent. In low carbon steel austenite exists above 1670 F (910 C). In austinetic stainless steels austenite exists between room temperature and the melting point. 

AUSTENITIC. A stainless steel or other single phase alloy which has a stable austenite structure between room temperature and the melting point. 

AUSTENITE GRAIN SIZE. This is the size of the grains of steel observed when the steel is heated to 1700 F and transforms from Alpha Iron (ferrite which exists at room termperature) to Gamma Iron (austenite which exists above 1600 F). The melt practice employed by the steel mill determines whether the steel will be coarse grain ASTM E 112 micro grain size 1-4, or fine grain ASTM E 112 micro grain size 5-8. The use of silicon as a deoxidizer in the melt practice normally produces coarse grain steel, where as, the proper addition of aluminum after silicon deoxidization will produce fine grain steel. 

AUSTENITIZE. The process of heating a carbon or alloy steel (existing as alpha iron) above 1330 F for partial transformation, or above 1600 F for complete transformation to austenite. 

Back to top


BATCH. The component of raw materials properly weighed, proportioned, and mixed for delivery to a processing unit. Also, the product output from a processing unit in which there is essentially no product output until all component materials are charged and processed. 

BLAST CLEANING. A process for surface cleaning or finishing metals using an air blast to impact abrasive or steel shot particles against the surface to be cleaned of scale, oxides or rust. 

BRAZE WELD  OR BRAZING: A process of joining metals using a nonferrous filler metal or alloy, the melting point of which is higher than 800°F but lower than that of the metals to be joined.

BRINELL HARDNESS TEST. A popular method for determining the hardness of a piece of metal by pressing a 10 mm hardened steel ball into the ground surface under 500-3000 Kg load. Comparison of the diameter of the impression with that of a known material hardness provides a relative indication of hardness of the piece of metal being tested. The result represents the Brinell hardness number which is the value obtained by dividing the applied load in kilograms by the surface area of the impression in square millimeters. 

BRITISH THERMAL UNIT (BTU). The amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Melting a pound of ice at 32°F requires 143 BTU. BSPT: British Standard Pipe Thread.

BUTT WELD:  A circumferential weld in pipe fusing the abutting pipe walls completely from inside wall to outside wall.

Back to top


CAPACITANCE. A measure of the amount of electric charge stored (or separated) for a given electric potential. The most common form of charge storage device is a two-plate capacitor.

CARBIDE PRECIPITATION. The migration and preferential combination of carbon with chromium in the grain boundaries of certain austenitic stainless steels. This carbide precipitation occurs when one part carbon combines with seventeen parts of chromium while the stainless steel is heated, or cooled, in the 800 F to 1500 F (427 C to 816 C) temperature range. 

CARBIDES. Compounds formed when carbon combines with one or more metallic elements. For example, in stainless steels when excess chromium carbides form, corrosion resistance can be reduced. 

CARBON. The principal non-metallic element which when combined with iron in controlled amounts below 2.0% forms the materials known as carbon steels. 

CARBON EQUIVALENT. A numerical value in weight percent, calculated from a mathematical equation, designed to relate the combined hardening effect of various alloying elements used in making carbon steel to an equivalent amount of carbon. Be reducing the carbon content in the steel and adding controlled amounts of various elements the desired strength levels can be achieved by proper heat treatment. In addition, the steel will have good weldability and low temperature notch toughness. The Carbon Equivalent (CE) formula is:
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Depending on customer and industry specifications, CE can be required as low as 0.40% maximum and as high as 0.50% maximum 

CARBON STEEL: A steel which owes its distinctive properties chiefly to the various percentages of carbon (as distinguished from the other elements) which it contains.

CARBURIZATION. Heating a carbon or alloy steel to the austenitizing temperature while in contact with a carbon rich atmosphere to cause absorption of carbon at the surface. 

CAST IRON. A generic term for a series of alloys primarily of iron, carbon, and silicon in which the carbon is in excess of the amount which can be retained in solid solution in austenite at the eutectic temperature. 

CAVITATION. The process where vapor bubbles in a flowing liquid collapse inside a control valve as the pressure begins to increase.

CEMENTITE. A form of iron carbide (Fe3C) contained in carbon and alloy steels. 

CHARPY IMPACT TEST. A series of three notched specimens are impact tested at a selected temperature to determine resistance (rated in foot pounds of energy) to crack initiation in metals. Refer to ASTM A-370 for details on specimen preparation, geometry and testing. See Joule for alternate unit of measurement. 

CHROMIUM. A metallic element added to steel to improve mechanical properties and increase resistance to oxidation, corrosion and wear. A minimum of 12% chromium is required to produce stainless steel.

CIRCUMFERENCE OF A CIRCLE: The measurement around the perimeter of a circle. To find the circumference, multiply Pi (3.142) by the diameter. (Commonly written as πd)

CLOSED LOOP. A control system that provides feedback to a controller on the state of the process variable.

COEFFICIENT OF EXPANSION: A number  indicating the degree of expansion or contraction of a substance. The coefficient of expansion is not constant and varies with changes in temperature. For linear expansion it is expressed as the change in length of one unit of length of a substance having one degree rise in temperature.

COLD JUNCTION. The end of thermocouple that is kept at a constant temperature in order to provide a reference point.

COLD WORKING. Deformation of a metal usually at room temperature. 

COLUMBIUM. A metallic element added to steel. In small amounts (

COMPACTED GRAPHITE IRON. A cast iron that has been treated in the liquid state so as to cause its graphitic carbon to occur in the compacted graphite shape in the as-cast condition. 

CONTACTS. Elements used to mechanically make or break an electric circuit.

CONTINUOUS WELD PIPE (CW). Hot finished pipe produced in continuous length from coiled skelp by forming rolls that shape the furnace heated skelp and form a butt weld joint by mechanical pressure. 

COPPER. A metallic element added to low to medium carbon and low alloy steel to improve resistance to various forms of atmospheric corrosion. 

CORROSION: The gradual destruction or alteration of a metal or alloy caused by direct chemical attack or by electrochemical reaction.

CREEP: The plastic flow of pipe within a system; the permanent set in metal caused by stresses at high temperatures. Generally associated with a time rate of deformation.

CRITICAL PRESSURE. The ratio of upstream to downstream pressure where the gas velocity out of the valve is sonic and further decreases in downstream pressure no longer increase the flow.

CRYOGENIC TEMPERATURE. Any selected temperature below -165 F (-108 C). 

Cv OR VALVE FLOW COEFFICIENT. The number of US gallons per minute of water at 60°F that will pass through the valve with a pressure drop of 1 psi.

Back to top


DEADBAND. The value of measurement between when a switch actuates and deactuates. 

DENSITY. The mass of a given substance per unit volume.

DERIVATIVE CONTROL. A method of changing the output of a controller in proportion to the rate of change of the process variable.

DEWPOINT. The temperature to which air must be cooled for the air to be saturated with water.

DIAMETER OF A CIRCLE: A straight line drawn through the center of a circle from one extreme edge to the other. Equal to twice the radius.

DIELECTRIC. The insulating material between the conductors of a capacitor.

DIELECTRIC CONSTANT. The ratio of the insulating ability of a material to the insulating ability of vacuum.

DIN. Deutsches Institut für Normung e.V., The German national organization for standardization and is that country's ISO member body.  DIN and miniDIN connectors, as well as DIN rails are several examples of older DIN standards that are today used around the world.

DIRECT CURRENT (DC). A current with a constant polarity.

DIRECT REDUCED IRON. Iron ores that have been reduced to essentially metallic iron by heat and reducing agents, but without melting, and processed into suitable shapes for use as a charge material in a melting operation. 

DOUBLE POLE DOUBLE THROW (DPDT) SWITCH. Two separate switches that operate simultaneously, each with a normally open and a normally closed contact and a common connection.

DOUBLE SUBMERGED ARC WELDED PIPE (DSAW). Cold finished pipe fabricated from individual lengths of plate which are pressed into a "U" shape and further into on "O" shape. The joint it tack welded and then a complete penetration submerged arc weld is made by the submerged arc welding method on both inside and outside surfaces. 

DRAWING. See Tempering. This is the old term for tempering and is now considered obsolete. 

DRIFT. A gradual change in an element over time when the process conditions are constant.

DRY BULB TEMPERATURE. The ambient air temperature measured by a thermometer that is freely expose to the air but shielded from other heating or cooling effects.

DUAL METAL. Two metals of different composition that are fusion bonded at all interfacial surfaces by casting metal of one composition against metal of a second composition. 

DUCTILE IRON. A cast iron that has been treated in the liquid state so as to cause substantially all of its graphitic carbon to occur as spheroids or nodules in the as-cast condition. 

DUCTILITY: The property of elongation, above the elastic limit, but under the tensile strength. A measure of ductility is the percentage of elongation of the fractured piece over its original length.

DYE PENETRATION INSPECTION (PT). The metal surface to be examined is coated with a red dyed penetrating oil. This oil is drawn into the surface defects by capillary action. After a sufficient time the excess oil, or dye, is removed from the surface to be examined and a white developer is sprayed over the entire surface. The dye, which has penetrated any surface defects, is drawn to the surface by the developer and the location, geometry and size of the defects can be determined. This test is considered to be non-destructive because it does not destroy the usefulness of the part being inspected. 

Back to top


ELASTIC  LIMIT: The greatest stress which a material can withstand without a permanent deformation after release of the stress. 

ELASTICITY. The ability of a material to stretch without undergoing plastic deformation and permanent distortion. 

ELECTRIC RESISTANCE WELD PIPE (ERW). Cold finished pipe made by a series of operations in which the flat rolled material is cold shaped into tubular form and welded at the seam by the application of pressure and heat. The heat is generated at the seam by the resistance to the flow of electric current applied through electrical contacts or an induction coil. 

ELECTROMAGNETIC TEST (ET). A nondestructive testing method which induces a magnetic field on the pipe under test. Discontinuities in the wall can be found and measured by variations in the surrounding magnetic field. 

ELONGATION. The extent that a material can plastically deform or permanently stretch and experiencing failure. In a tensile test this is stated as percent elongation. 

EMISSIVITY. The ratio of energy radiated by the material to energy radiated by a black body at the same temperature. It is a measure of a material's ability to absorb and radiate energy.

EROSION: The gradual destruction of metal or other material by the abrasive action of liquids, gases, solids or mixtures thereof.

ERW WELD DUCTILITY TEST. Specimens from ERW pipe are flattened cold between parallel plates. The weld is located 90 degrees to the parallel plates as described in flattening tests. 

ETCHING. The process of applying acids or other reagents to a metallic surfaces for the purpose of revealing structure details or surface characteristics. See Acid Etch Test. 

Back to top


FERRITE. A solid solution in which alpha iron (body centered cubic crystal structure) is the solvent. In low carbon steel ferrite exists between room temperature and approximately 1330 F. 

FERRITIC GRAIN SIZE. This is the size of the ferrite particles which along with pearlite (a lamellar aggregate of fine alternating platelets of ferrite and iron carbide) make up the substructure of each austenite grain in low carbon and alloy steels. When Ferrite Grain Size is specifically required in addition to, or in lieu of, Austenitic Grain Size this requirement should be clearly stated. Ferrite should then reported as ferrite particle size, and not as grain size, to avoid confusing it with austenitic grain size. 

FERRITIC MALLEABLE. A ferrous alloy that is cast as white iron but which is converted by an appropriate heat treatment to a microstructure of temper carbon embedded in a ferritic matrix essentially free of pearlite and carbide. 

FINE GRAIN STEEL. Carbon and alloy steels which have been produced by a fine grain melt practice at the steel mill. Modern melt practice employs silicon killing to remove to remove excess oxygen from the molten metal, then sufficient aluminum is added to form aluminum oxides which act as nuclei for the formation of fine austenitic grains. 

FLAKE GRAPHITE. An irregularly shaped particle of graphite usually appearing in a polished section as curved plates, such as found in gray cast irons. 

FLARE TEST. A destructive test to check the weld quality and ductility of pipe by tapered expansion over the apex of a cone of specified dimensions, usually 60 degrees. 

FLATTENING TEST. A destructive test where a ring cut from a length of pipe cold flattened to establish if the ductility, soundness and weld quality (for welded pipe) meet the specific requirements. 

FOOT POUNDS ENERGY. The impact energy rated in foot pounds of force required to break charpy impact specimens. See Joules as an alternate unit of measurement. 

FORGED. The process of forming ingots, blooms and billets into wrought shaped products by applying pressure at elevated temperatures using a press. Some austenitic stainless steels and nonferrous alloys are formed at room temperature. 

FORMED. The process of forming tube or plate into shaped products by applying pressure at elevated temperatures using a press. Some austenitic stainless steels and nonferrous alloys are formed at room temperature. 

FUZZY LOGIC. A system that uses mathematical or computational reasoning based on fuzzy sets derived from analog inputs.

Back to top


GAGE PRESSURE (psig). The measure of force per area exerted by a fluid using atmospheric pressure as the zero reference.

GAIN. The ratio of change in output to the change in input of a process.

GALVANIZING. The process of applying a coating of zinc to the finished product to provide corrosion protection. The coating can be applied by hot dipping or electrolytic deposition. 

GAMMA IRON. See Austenite. 

GRAIN FLOW. The macro-structure characteristics of a part, after polishing and etching, which reveals the principle direction in which the metal has been worked by mechanical methods such as pressing, hammering or rolling. 

GRAIN SIZE. The term normally applies to the austenitic grain size as determined in carbon and alloy steels by the McQuaid-Ehn test. ASTM E 112 defines methods for rating grain size. When specifying grain size it should be clearly stated when austenitic grain size is required and when ferrite particle size is required. 

GRAPHITIZATION. The transformation of carbon, during prolonged heating at elevated temperatures, into graphite which embrittles the steel. 

GRAY IRON. Cast iron that has a relatively large proportion of the graphitic carbon present in the form of flake graphite. The metal has a gray fracture. 

GUIDED-BEND TEST. A test for submerged arc welded pipe where a specimen 1-1/2" x 6" conforming to requirements is bent approximately 180 degrees in a special jig with maximum bending occurring at the welding zone to check the ductility of the weld, and the heat treated zone. 

Back to top


HARDNESS. A measure of the resistance of a material to indent when an indentor of known geometry is impressed against a surface under a given load. 

HEAT AFFECTED ZONE. This is the thermally affected area of metal immediately adjacent to the weld in a part. Normally welding conditions must be controlled, or some form of preheat of post-heat treatment applied after welding, to assure that this area does not cause premature failure of the part in service. 

HEAT TREATMENT. This is a predetermined combination of heating and cooling operations applied to a metallic material in the solid state so desired physical and/or mechanical properties are attained. See annealing, normalizing, tempering and stress relieving which are the most common types of heat treatment. 

HOT JUNCTION. The joined end of the thermocouple that is exposed to the process where the temperature measurement is desired.

HUEY TEST. An accelerated corrosion test designed for evaluating austenitic stainless steels (300 series). The sample approximately 2" long x 1" wide x 1/4" thick is machined and ground on all six sides to remove any disturbed metal. It is weighed and boiled in a nitric acid solution for five 48 hour periods. After each period it is weighed again and measured, and the total weight loss and size reduction is converted into corrosion rate per year. This test may be preceded by the Oxalic Acid Etch Test. 

HUMIDITY. The amount of water vapor in a given volume of air or gas.

HYDROSTATIC PRESSURE. The pressure due to the head of a liquid column.

HYDROSTATIC TEST. A test where a specific water pressure produces a stress to a percentage of the minimum yield strength in the material. It is applied internally to the full length of pipe to be sure it is free from leaks and capable of withstanding a specific pressure. 

HYSTERESIS. A property of a device or instrument whereby it gives different output values in relation to its input values, depending on the directional sequence in which the input values have been applied [IEC 61298-2]

Back to top


IMPACT STRENGTH. See Charpy Impact Test. 

IMPEDANCE. The opposition in an electric circuit to the flow of an alternating current consisting of inductive reactance, ohmic resistance and capacitive reactance.

INACCURACY. Maximum positive and negative deviation from the specified characteristic curve observed in testing a device under specified conditions and by a specified procedure [IEC 61298-2]  NOTE 1: Accuracy is defined in IEC 60050-300, definition 311-06-08.  NOTE 2: The term inaccuracy is sometimes referred to as measured accuracy. This term should not be used.

INDUCTION HEATING. A process of heating by electrical induction. 

INDUCTIVE LOAD. Current passing through wound or coiled wire creates a magnetic field that in turn produces mechanical work.

INGOT. A casting of metal which has a square, rectangular or round cross-section, and is of sufficient length for rolling or forging into blooms, billets, or slabs, intended for conversion into forged products. In the case of very large parts the ingot may be forged directly into the desired product. 

INOCULATED IRON. Cast iron, either liquid or solid, to which one or more inoculating alloys have been added while the iron was in the molten state. 

INOCULATING ALLOY. An alloy added to molten iron for the principle purpose of nucleating a primary phase such as graphite. Inoculating alloys are frequently used to avoid the formation of primary carbide by enhancing the nucleation of graphite. 

INTEGRAL CONTROL. A method of changing the output of a controller by an amount proportional to the error and the duration of that error.

INTERGRANULAR CORROSION. A preferential attack at the grain boundaries. In the case of austenitic stainless steels (300 series) the formation of chromium carbides in the grain boundaries at elevated temperatures depletes the chromium content at the surface of each grain. This leaves the areas around the grains susceptible to certain types of corrosion. 

IRON. The principle element in carbon, alloy and stainless steels. These steels are called ferrous, or ferrous based, materials. 

Back to top


JOMINY HARDNESS TEST. A test designed to determine the ability of a grade of steel to harden by uninterrupted cooling of one end surface of a 1" diameter bar, and measuring the change in hardness from the end of the bar to the point where hardness remains consistently low. 

JOULE. A unit defining work, or energy, related to Charpy Impact Testing. One Joule is approximately 0.74 foot pounds. 

Back to top


KILLED STEEL. Steel which has been treated in the molten state with silicon and/or deoxidizers such as aluminum to reduce the oxygen content of the molten steel to a minimum. This treatment quiets the metal and permits it to densify during solidification. All steels used in the manufacture of flanges and fittings are made. 

Back to top


LAMINAR FLOW. Smooth fluid flow that has a parabolic flow profile with no mixing between streamlines.

LINEARITY. Ability of a measuring instrument to provide an indication having a linear relationship with a defined quantity other than an influence quantity. [IEC 60050-300]  NOTE: The method of expression of lack of linearity is different for different kinds of instruments and is established in each particular instance.


LONG-TERM SPAN DRIFT. The amount of change of a measured reading with 90% of full scale range pressure applied and constant ambient conditions over a given period of time which is typically quoted as an annual figure. [IEC 61298-2]

LONGITUDINAL TENSILE TEST. For small diameter sizes full size tubular sections are tested. For larger sizes longitudinal test specimens are obtained from strips cut from the tube. For welded pipe. Specimens are located approximately 90 degrees from the weld. 

LOT. A finite quantity of a given product manufactured under production conditions that are considered uniform. 

LOW PRESSURE STEAM. As defined by ASME, steam under 15 psi pressure.

LOW TEMPERATURE. Any selected temperature between room temperature of 68 F (20 C) and -165 F (-108 C). 

Back to top


MACRO-STRUCTURE. The appearance of a cross-section of a part at low magnification, after polishing and acid etching, which reveals grain flow, segregation, soundness and other internal structural characteristics. 

MAGNETIC PARTICLE INSPECTION (MT). The inspection of a carbon or alloy steel part which has been magnetized and sprayed with fine magnetic particles which will adhere to surface indications such as cracks, laps and seams. This inspection method is not applicable to non-magnetic materials, such as, austenitic stainless steels and nonferrous alloys. 

MALLEABLE IRON. A cast iron of such composition that it solidifies as white iron, which upon proper heat treatment is converted to a metallic matrix with nodules of temper carbon. 

MALLEABLEIZE. To convert white iron into malleable iron through an appropriate graphitizing heat treatment. 

MANGANESE. A metallic element added to steel to increase hardenability, and to combine with excess sulfur to form manganese sulfides which remain solid at elevated temperatures thereby improving the hot workability of steels. 

MANUAL RESET. A control that must have human input before it will return to its normal state from an alarm state.

MARTENSITE. This phase of steel has the same composition as austenite from which it transformed. The difference being that martensite is a super-saturated solid solution in alpha iron (ferrite) with a body-centered tetragonal crystal lattice. Austenite is a super saturated solid solution of carbon in gamma iron with a face-centered cubic crystal lattice. 

MARTENSITIC. A stainless steel (400 series) which transforms on cooling from austenite to martensite and remains martensitic at room temperature. 

MAXIMUM SURGE PRESSURE. Safe pressure for the switch housing but which may damage the mechanism by continuous or repetitive application.

McQUAID-EHN GRAIN SIZE. The austenitic grain size developed in steels by carburizing at 1700 F (927 C) followed by slow cooling and determined in accordance with ASTM method E 112. 

MECHANICAL TUBING. Tubing used for a variety of mechanical and structural purposes and not necessarily designed for the carrying of fluids or gases under pressure. 

MICRO ALLOYED STEELS. Grades of plain carbon steel which have been melted with deliberate additions of small quantities of metallic elements known to improve hardenability, tensile properties and impact strength and toughness; without adversely affecting weldability. 

MICRO-STRUCTURE. The appearance of a metal surface at high magnification (greater than 10 diameters), after fine polishing to remove all scratches and etching, which reveals structural characteristics such as grain size, inclusions, and the amount and configuration of such metal constituents as ferrite, pearlite, austenite and martensite. 

MILS LATERAL EXPANSION (MLE). The increase in thickness (measured in mils, 1 mil = 0.001") at the surface of a Charpy specimen directly opposite the notch where the narrow edge of the pendulum strikes the specimen during testing. E.g., a full size Charpy specimen has a square 0.394" x 0.394" cross section. If the surface opposite the notch expands after being struck from 0.394" to 0.419", the Mils Lateral Expansion equals 25 MLE. (See ASTM method A 370). 

MOLYBDENUM. A metallic element added to steel which goes into solid solution and also forms carbides. Molybdenum effectively increases the strength of steel at elevated temperatures and reduces the susceptibility to temper brittleness in chromium steels. It also retards graphitization in steels designed for service at elevated temperatures. In stainless steels it improves resistance to certain types of corrosive media. 

MOTTLED IRON. A cast iron containing a mixed structure of gray iron and white iron of variable proportions. The fracture has a mottle appearance. 

Back to top


NEMA. The National Electrical Manufacturers Association, a trade association in the US of electrical equipment manufacturers that develops many industry technical standards in particular is the standard for electrical equipment enclosures.

NICKEL. A metallic element which forms a solid solution with iron when added to steel. It does not form carbides, but assists in hardening to improve tensile properties and resistance to embrittlement at low temperatures. Nickel in excess of 7% is responsible for making the 300 series stainless steels austenitic. 

NIST. The National Institute of Standards and Technology, is a nonregulatory agency of the United States Department of Commerce’s Technology Administration. The institute provides standard references and calibration services.

NOBIUM. See Columbium. Nobium is primarily the European word for columbium. It is not accepted for use by the American Society for Testing and Materials (ASTM). 

NODULAR GRAPHITE. Spheroid shaped graphite typically found in ductile irons and compact clusters of graphite typically found in malleable irons. 

NODULARITY. The volumetric proportion of spheroid or nodular graphite to total graphite in a ductile iron or a compacted graphite iron matrix. 

NODULIZING ALLOY. An alloy added to molten iron for the primary purpose of causing the formation of spheroid graphite during solidification. 

NORMALIZING. A heat treatment for carbon and alloy steel which involves heating above the upper critical transformation temperature (to approximately 1650 F, 900C), holding at temperature about one hour and cooling to room temperature in still air. This process homogenizes the steel by reducing carbon segregation and refining the ferrite and pearlite micro-constituents of steel. It also reduces the stress differential created when lighter sections of a forged part cool faster than heavier sections, and improves machineability. 

NORMALLY CLOSED SWITCH. A switch in which the contacts are normally closed. Actuation opens the contact.

NORMALLY OPEN SWITCH. A switch in which the contacts are normally open. Actuation closes the contacts.

NOTCH TOUGHNESS. The ability of a steel or other metal alloy containing a notch to resist fracturing under load. See Charpy Impact Test. 

NPT. National Pipe Thread.

NSF. A not-for-profit, non-governmental organization that develops standards and provides product certification and education in the field of public health and safety.

NULL SWITCH. A floating contact switch with a zone of no contact.  Often used to operate reversible motors.

Back to top


OIL QUENCHING. A cooling method for hardening steels, heated above the upper critical temperature, by immersion into liquid oil. This cooling method is normally reserved for medium to high carbon and alloy steels which may crack if hardened by quenching in water. 

OXALIC ACID ETCH TEST. In this test a highly polished and acid etched (Oxalic acid) surface of austenitic stainless steel is examined at 250 X to 500 X magnification to determine the extent of grain boundary attack. Steels passing this test normally to not require examination by hot acid tests as the Huey Test. See ASTM method A 262 for details. 

Back to top


PASSIVATING OR IMMUNIZING. The acid treatment of stainless steels to make them more resistance to corrosion through the formation of a surface film of chromium oxide. 

PEARLITE. A lamellar microstructure in carbon and alloy steels which consists of alternate layers of ferrite (alpha iron) and cementite (iron carbide) resembling mother-of-pearl. 

PENETRATING INSPECTION (PT). See Dye Penetrant Testing. 

pH. An indication of the acidity or alkalinity of a solution in units ranging from 0 (most acidic), to 7 (neutral), to 14 (most alkaline).

PHOSPHORUS. A metallic element normally inherent in steel as a residual from the smelting process. It is normally kept below 0.05% in carbon and alloy steels because of its strong influence on hardness and adverse affect on transverse toughness. When added to free cutting steels in larger quantity it improves machineability of mechanical parts. Sulfur has a similar effect on steel properties. 

PIG IRON. The high carbon iron product obtained by the reduction of iron ores, typically in a blast furnace or an electric furnace, and cast into uniform shapes (pigs) having physical and chemical characteristics of the material, as foundry melting stock. 

PICKLING. The removal of surface oxides from metals by immersion in a reducing acid bath. Occasionally a blackish surface smut (a non-adhering carbon film) is produced which must be removed by scrubbing or immersion in an oxidizing acid bath. 

PIPE. Hollow cylindrical product that is pressure tested and distinguished from pressure tubing by the fact that it is produced in specific sizes with relatively more liberal tolerances. 

PRESSURE DROP. The difference in upstream and downstream pressure of the fluid flowing through a valve.

PRESSURE TUBING. Tubing used to conduct fluids under pressure or at elevated temperatures or both, and produced to stricter tolerances than pipe. 

PRIMARY CARBIDE. Carbide precipitated in cast iron during solidification. 

PROPORTIONAL CONTROL. A method of changing the output of a controller by an amount proportional to the error.

PROPORTIONAL-INTEGRAL CONTROL (PI). Proportional and integral control combined.

PROPORTIONAL-INTEGRAL-DERIVATIVE CONTROL (PID). Proportional, integral, and derivative control combined.

Back to top


QUENCHING. An accelerated cooling method used for increasing the hardness and strength of carbon and alloy steels, which is normally followed by a tempering cycle. Quenching normally implies immersion in a liquid such as water or oil. In the solution treatment of austenitic stainless steels and nickel based alloys a water quench is used to keep carbides in solution. The quench cycle is normally complete when the item being quenched cools to around 212 F (100 C). 

Back to top


RADIOGRAPH. A photographic film placed behind the object being radiographed, which shows differences in absorption created by discontinuities, thickness variations or density after being developed. 

RADIOGRAPHIC INSPECTION (RT). A non-destructive method of internal examination in which the metal is penetrated by a beam of x-ray or gamma radiation. 

RADIUS OF A CIRCLE: A straight line drawn from the center to the extreme edge of a circle.

RANGE. The span of rates within which the sensing element of a given switch can be set to actuate an electric switch.

RATED PRESSURE. The maximum pressure that the actuating components of the switch in contact with the media can withstand continuously and/or repeatedly without risk of permanent damage.

REDUCTION OF AREA. As determined in a tensile test this is the difference between the cross-sectional area of the test specimen and the smallest area at the point of rupture. 

RELATIVE HUMIDITY. The ratio of the quantity of water vapor in the air to the quantity of water vapor required for saturation at the same temperature.

REPEATABILITY. The closeness of agreement between the results of successive measurements of the same measured, carried out under the same conditions of measurement, i.e.: by the same measurement procedure; by the same observer; with the same measuring instruments, used under the same conditions; at relatively short intervals of time. [IEC 60050-300]

REPETITIVE ACCURACY. The ability of a switch to operate repetitively at its set point under consistent conditions.

RESIDUAL ELEMENTS. Those metallic elements which are not deliberately added to a grade of steel as alloying elements, but are present because they were inherent in the ore, or scrap, which was used in making the heat of steel. Residual elements are usually present in small quantities under 0.25% each for nickel, chromium, and copper, and under 0.05% each for columbium, titanium, aluminum, etc. 

RESPONSE TIME. The time it takes an element to respond to a change in the value of the measured variable or to produce a change in the output signal.

ROCKWELL HARDNESS TEST. A method for determining the relative hardness of a metal by impressing a diamond indentor, or a 1/16" or 1/8" ball into a ground surface with a prescribed load not exceeding 150Kg. This test is normally used on small hardened parts, or on surfaces where the larger impression made by the Brinell hardness test is undesirable. 

ROTAMETER. A variable area flowmeter consisting of tapered tube and a float.

RS-232. (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment).

RS-485. (Now known as EIA-485) is an OSI model physical layer electrical specification of a two-wire, half-duplex, multipoint serial connection.

Back to top


SAMPLE. One or more portions of a liquid or solid material taken in an unbiased manner from a batch, heat, lot, or process stream to be representative of the whole, for subsequent testing to determine the chemical, physical, mechanical, or other quality characteristics of the material, or combination thereof. 

SATURATION POINT. The point at which condensation is formed.

SEAMLESS PIPE. Hot finished pipe made from a reheated billet which is forged into a bottle shape, elongated and subsequently stretched over a mandrel bar by pushing through a series of roller dies. After reheating, reducing rolls give it its final dimensions. 

SENSITIZATION. The condition resulting from heating, or slow cooling, austenitic stainless steels in the temperature range of 800 F to 1600 F (427 C to 871 C), which permits the formation of chromium carbides at the grain boundaries. The formation of carbides reduces the chromium content at the surface of the grains, thereby, reducing corrosion resistance. 

SERIAL TRANSMISSION. Sending one bit at a time on a single transmission line.

SET OR ACTUATION POINT. The exact rate which will cause the electric switch to actuate.

SHEAR FRACTURE. After Charpy specimens are broken, and the energy absorbed during breaking recorded, the fractured surfaces are visually examined to determine if the fracture has a brittle or ductile appearance. Fractured surfaces which contain both brittle (cleavage) and ductile (shear) areas are classified as to the percentage of shear (ductile) area. A normally specified requirement is 50% minimum shear, which is considered by most pipeline material specification writers as representative of a material's ability to resist crack propagation after a fracture has been initiated. 

SILICON. A non-metallic element added to steels to deoxidize the molten metal prior to solidification in the ingot mold. In solution silicon strengthens ferrite in steel. It also increases the oxidation resistance of austenitic stainless steels at elevated temperatures. 

SINGLE-POLE SINGLE THROW (SPST) SWITCH. A switch that only has one of either a normally open or a normally closed contact.

SINGLE-POLE DOUBLE-THROW (SPDT) SWITCH. A switch combining both normally open and normally closed switch contacts.

SKELP. Steel plate or sheet from which welded tubing or pipe is manufactured. 

SMELTING. The heating process for removing metals from their ores. A blast furnace is commonly used for converting iron ore into metallic iron. 

SOCKET FITTING: A fitting used to join pipe in which the pipe is inserted into the fitting. A fillet weld is then made around the edge of the fitting and the outside wall of the pipe.

SOLDERING: A method of joining metals  using fusible alloys, formerly tin and  lead, having melting points under 700°F

SOLID STATE. Any element that controls current without moving parts, vacuum gaps or heated filaments.

SOLUTION ANNEALING. Also known as annealing, or carbide solution treating, this process involves the heating of austenitic stainless steels and alloys to an elevated temperature known to ensure that carbides will be dissolved into austenite. After sufficient holding time the material is rapidly cooled, or quenched, to prevent carbides from reforming. 

SPAN. The difference between the highest and lowest numbers in a range.

SPAN TEMPERATURE COEFFICIENT. The maximum amount the span reading could change at any point within the compensated temperature range. This error is typically expressed as a percentage of full scale output of reading. It can also be expressed as percentage of full scale per °C, °F or K e.g. ±0.02%FS/°C.

SPECIFIC GRAVITY. The ratio of the density of a fluid to the density of a reference fluid.

STABILIZATION. The alloying of austenitic stainless steels with elements such as columbium, molybdenum, or titanium which combine with excess carbon to prevent sensitization and the formation of chromium carbides. 

STATIC PRESSURE. The pressure exerted by a fluid at rest.  The outward push of a fluid against the walls of a container.

STEEL SCRAP. Discarded steel or steel products, generally segregated by composition and size or "grade", suitable for melting. 

STRAIN: Change  of shape or size of a body  produced by the action of a stress.

STRESS: The intensity of the internal, distributed forces which resist a change  in the form  of a body. When external forces act on a body they are resisted by reactions within the body  which are termed  stresses.

COMPRESSIVE STRESS: One that resists a force  tending to crush  a body.
SHEARING STRESS: One that resists a force  tending to make  one  layer of a body slide  across another  layer.
TENSILE  STRESS: One that resists a force  tending to pull a body  apart.
TORSIONAL STRESS: One that resists forces  tending to twist a body.

STRESS RELIEVING. The reduction of residual stresses in a metal part, or welded fabrication, either thermally, or mechanically. Stress relieving is generally considered to be a thermal treatment, wherein the part is heated to a suitable sub-critical temperature and held at temperature long enough to relieve the major stresses and then air cooled. Stress relieving should not be confused with tempering, and must be done at least 50 F to 100 F below the temperature at which the part being stress relieved was tempered. 

SULFUR. A non-metallic element normally inherent in steel as a residual from the smelting process. It is normally kept below 0.045% in carbon and alloy steels because of its adverse affect on transverse toughness. When added to free cutting steels in larger quantity it improves machineability of mechanical parts. Phosphorous has a similar effect on steel properties. 

Back to top


TEMPER BRITTLENESS. The loss of notch toughness in some steels when they are heated in the temperature range of 850 F to 1100 F (450 C to 590 C). 

TEMPER CARBON. Compact aggregates or nodules of graphite found in malleable iron as a result of heat treatment. 

TEMPERATURE COMPENSATION. The correction for the influence of temperature on a measurement.

TEMPERING. The thermal treatment at a predetermined temperature below the critical range (below 1300 F, 700 C) which follows the quench cycle in heat treatment of carbon and alloy steels. It reduces the as-quenched hardness and significantly improves toughness and impact strength, particularly at low temperatures. Normalized parts may also be tempered to reduce hardness and improve toughness and impact strength. 

TENSILE STRENGTH. The ultimate stress which a metal undergoes prior to failure as determined by the maximum load observed during testing divided by the cross-sectional area of the tensile specimen. True tensile strength would be the maximum load divided by the actual cross-sectional area of the specimen at the moment the load reading was observed. (See ASTM method A 370). 

TENSILE TEST. The testing of a tensile specimen to determine the yield strength, ultimate strength, elongation and reduction of area. (See ASTM method A 370). 

TEST BAR. A bar-shaped coupon that is tested with or without subsequent preparation for the determination of physical or mechanical properties. 

TEST COUPON. Specially designed casting, or portion thereof, that is used to provide a representative sample of the iron from which it was cast. 

TEST LUG. A sample produced as an appendage on a casting, that may be removed and tested to qualify the casting or the iron from which it was produced. 

TEST SPECIMEN. A test object, suitable prepared from a sample, for evaluation of the chemical, physical, mechanical, or metallurgical quality of the sample. 

3-A. 3-A Sanitary Standards Inc., A non-profit association representing equipment manufacturers, processors, regulatory sanitarians, and other public health professionals that creates standards and accepted practices for dairy and food processing equipment and systems.

TOTAL PRESSURE. The sum of velocity and static pressure. 

TRANSDUCER. Any device that generates an electrical signal from physical measurements.

TRANSMITTER. A device that translates the low-level output of a sensor or transducer to a higher level signal suitable for transmission to a site where it can be further processed.

TRANSVERSE TENSILE TEST. The specimen shall be located 90 degrees to the axis of the pipe. Not applicable for sizes larger than 8 5/8" in outside diameter. 

TRANSVERSE WELD TESTS. Specimen is taken 90 degrees to the weld with the weld at the center of the specimen. Not applicable for sizes than 8 5/8" in outside diameter. 

TREATED IRON. Molten cast iron to which all basic alloys and nodulizing alloys have been added but not necessarily all inoculating alloy additions. 

TURBULENCE: Any deviation from  parallel flow in a pipe due to rough  inner walls, obstructions or directional changes.

TURBULENT FLOW. Fluid flow in which the flow profile is a flattened parabola, the streamlines are not present, and the fluid is freely mixing.

TURNDOWN RATIO. The ratio of the maximum to minimum measurable value that can still produce full-scale output. 

Back to top



ULTRASONIC INSPECTION (UT). A nondestructive test which can detect defects in solid metal objects by directing controlled ultra-high frequency sound waves into the part being inspected. Ultrasonic response of the area being examined is monitored on the screen of a cathode ray tube. The location, size and orientation of defects can be determined. Also, wall thickness variations can be measured and corrosion rates can be monitored. 

Back to top


VANADIUM. A metallic element added to steel to improve hardenability and provide secondary hardening. It promotes fine grain by raising the grain coarsening temperature of austenite. 

VELOCITY: Time rate of motion in  a given  direction and sense, usually expressed in feet per second.

VELOCITY PRESSURE (DYNAMIC PRESSURE). The pressure exerted by the velocity of a fluid.  Can be measured by the difference between total and static pressure.

VISCOSITY: The resistance of a fluid to flow when subjected to shear stress.

VOLUME OF A PIPE: The measurement of the space within the walls  of the pipe. To find  the volume of a pipe, multiply the length  (or height) of the pipe by  the product of the inside  radius  times the inside  radius  by Pi (3.142). Commonly written as V = hpr2

Back to top


WATER QUENCHING. See Quenching. 

WELD. The fused metal seam which holds two, or more, pieces of metal together. 

WELDABILITY. The capacity of certain metals and their alloys to be fabricated by welding into structures suitable for the intended service requirements. Various residual, or excessive, elements and inclusions may prohibit the formation of sound welds. 

WELDING. The process of joining two, or more, pieces of metal together by melting and fusing the parent metal edges together with, or without, filler metal. 

WET BULB TEMPERATURE: The lowest temperature that can be obtained through the cooling effect of water evaporating into the atmosphere.

WHITE IRON. Cast iron in which substantially all of the carbon is in solution and in the combined form. The metal has a white fracture. 

WROUGHT METAL. A mechanically worked and toughened metal as opposed to an as-cast brittle metal. 

Back to top


X-RAY. See Radiographic Inspection (RT). 

Back to top


YIELD STRENGTH. The stress under load at which the proportionality between stress and strain in a tensile specimen is no longer equal. From this point on the specimen elongates at a reduces stress level with the increasing load until rupture occurs. 

Back to top


ZERO TEMPERATURE COEFFICIENT. The maximum amount the output reading at zero pressure might deviate over the compensated temperature range.  This error is typically expressed as a percentage of full scale output of reading. It can also be expressed as percentage of full scale per °C, °F or K e.g. ±0.02%FS/°C.

ZYGLO INSPECTION (PT). A liquid penetrating inspection method using a fluorescent penetrating oil and requiring black light to detect surface indications and defects.

Back to top

Let Us Help...

Not sure what you need? Special Options? Immediate help? Give us your requirements and we will contact you as soon as possible.


“I like buying Apollo safety/relief valves from Stritt & Priebe. They’re made in America and Stritt stocks the valves in the orifices I need for any application. The valves are set & tested at Stritt’s facility, where I can get them when I need them. They totally know what they're doing. You're in Great hands ~ !!!”


> 34 yrs experience

Irish Companies


Board Certified
Valve Repair

Holding Stamp #14