Glossary of Terms
All steels contain carbon and small amounts of silicon, sulfur, manganese and phosphorus. Steels that contain intentional additions of elements other than these or in which silicon and manganese are present in large amounts for the express purpose of improving or altering any of the physical or mechanical properties of the steel are termed alloy steels.
A general term referring to the thermal treatment process involving heating and cooling, usually applied to change mechanical or physical properties, to produce a desired microstructure.
Annealing (Bright Annealing):
An annealing process usually carried out in a controlled atmosphere furnace using a reducing atmosphere to achieve desired mechanical properties with minimum surface oxidation. The tube surface is relatively bright.
An annealing process in which a steel is heated to a temperature that is above the upper transformation range and then cooled in air. A slight surface oxidation occurs during this process. The tube surface has a black or blue color.
Annealing (Solution Annealing):
An annealing process in which stainless steel is heated to a suitable temperature to help ensure the solution of constituents, such as chromium carbides, and cooled rapidly to hold these constituents in solution.
ASM (American Society for Materials International):
A professional society of Material Scientists and Engineers dedicated to the collection and distribution of information about materials and manufacturing processes.
ASME (American Society of Mechanical Engineers):
An organization of engineers dedicated to the preparation of design code requirements and material and testing standards. Adopts, sometimes with minor changes, specifications prepared by ASTM. The adopted specifications are those approved for use under the ASME Boiler and Pressure Code and are published by ASME in Section II of the ASME Code. The ASME specifications have the letter “S” preceding the “A” or the “B” of the ASTM specifications. The “SA” series are for iron base materials, while the ‘SB”” series are for other materials, such as nickel base, copper, etc.
ASTM (American Society for Testing and Materials):
A body of industry professionals involved in writing universally accepted steel material and test specifications and standards. The “A” series of material specifications are for iron base materials, while the “B” series are for other materials, such as nickel base, copper, etc.
A non-magnetic metallurgical phase having a face-centered cubic crystalline structure. Except for steel compositions having at least 6% nickel, austenite is typically only present at temperatures above 1333 ˚F (723 ˚C).
These grades of stainless steels (300 Series and some 200 Series) have chromium (roughly 18% to 30%) and nickel (roughly 6% to 20%) as their major alloying additions. They have excellent ductility and formability at all temperatures, excellent corrosion resistance and good weldability. In the annealed condition, they are nonmagnetic. Some have the ability to be hardened by cold rolling as a final step. These grades are usually non-magnetic and are used for applications requiring good general corrosion resistance, such as food processing, chemical processing, kitchen utensils, pots and pans, brewery tanks, sinks, wheel covers and hypodermic needles.
A test for determining relative soundness and ductility of a metal to be formed. The specimen is bent over a specified diameter through a specified angle. In welded tubing, the weld is of primary interest.
An angular cut on the ID or OD of a tube.
The internal pressure that will cause a piece of tubing to fail by exceeding the plastic limit and tensile strength of the material from which the tube is fabricated.
The amount of curvature or deviation from exact straightness over any specified length of tubing.
Semi-killed steel that has characteristics similar to those of rimmed steels, but to a degree intermediate between rimmed and killed steel. The capping operation limits the time of gas evolution and prevents the formation of an excessive number of gas voids within the ingot.
Carbon Steel Tube:
Steel tube containing only residual quantities of elements other than carbon and manganese. Typical industrial AISI designated grades include 1008, 1010, 1020, 1026, 1030, 1035 etc.
(1) A beveled surface to eliminate an otherwise sharp corner. (2) A relieved angular cutting edge at a tooth corner.
Charpy Impact Test:
A pendulum-type single blow impact test in which the specimen, usually notched, is supported at both ends as a simple beam and broken by a falling pendulum. The energy absorbed, as determined by the subsequent rise of the pendulum, is a measure of impact strength or notch toughness. See also impact testing.
An analysis of the metal after it has been rolled or forged into semi-finished or finished forms. It is not a check on the ladle analysis, but is a check against the chemistry ordered.
Coefficient of Thermal Expansion:
A physical property value representing the change in length per unit length, the change in area per unit area or the change in volume per unit volume per one degree increase in temperature.
The process of pulling a tube through a die and over a mandrel to reduce its diameter and/or wall thickness to a specific outside diameter, inside diameter or wall thickness. Higher tensile properties, tighter dimensional tolerances, and improved surface finish are obtained due to the cold working at room temperature.
Used to describe tubing where the center of its inside diameter is consistent with the center of its outside diameter resulting in no variation of wall thickness. By virtue of the fact that welded tubing is fabricated from precision rolled flat stock, concentricity is inherent with a roll-formed, welded tube.
Chemical or electrochemical deterioration of a metal or alloy.
Corrosion associated with the presence of two dissimilar metals in a solution (electrolyte). In principle, it is similar to bath-type plating in the sense that the anode surface has lost metal (corroded).
Corrosion that occurs preferentially along the grain boundaries of the alloy.
Non-uniform corrosion usually forming small cavities in the metal surface.
The ability to resist attack by corrosion.
Refers to tubing ordered to a specified length and permitting a tolerance of a standardized fraction of an inch over, but nothing under, the specified length.
Removal of a small ridge of metal formed by upset during a machining or cutting operation.
The loss of carbon from the surface of ferrous alloy as a result of heating in a medium that reacts with the carbon.
The mass per unit volume of a substance, usually expressed in the tubing industry in pounds per cubic inch.
Any of the mechanical tests performed on an expendable sample of tubing to check physical properties. These tests include: tensile, yield, elongation, hardness, flare, flattening, bend and burst.
Dimensions of Tubing:
A round tube section has three dimensions, any two of which may be specified. The three dimensions are outside diameter (OD), inside diameter (ID), and wall thickness (t or W). Nominal as applied to any of these dimensions refers to the theoretical or stated single value of that dimension. The dimensions ordinarily specified by the customer are termed “nominal”; maximum and minimum referring to the greatest and least values of any dimension. Average dimensions are those secured by averaging a series of micrometer readings.
The ability of a tube to deform plastically. Frequently, elongation during tensile testing is used as a measurement of this property.
Duplex Stainless Steels:
Steels exhibiting both austenitic and ferritic phases and characteristics.
Dye Penetrant Inspection:
Non-destructive test employing dye or fluorescent chemical and sometimes black light to detect surface defects.
The displacement of the ID of the tube with respect to its OD Eccentricity results in the variation of wall thickness.
Eddy Current Testing:
A nondestructive testing procedure that is a continuous process performed on the tubular products during fabrication and in final inspection. It is by nature an electrical test that utilizes fluctuations in magnetic field strength to check tubing (against a calibrated standard) for possible defects, such as holes, cracks, gouges, etc., on both inside and outside surfaces of the tube.
A measure of the maximum stress that may be applied to a tube without leaving a permanent deformation or strain after the stress is released.
The amount of permanent extension in the vicinity of the fracture in the tension test; usually expressed as a percentage of the original gauge length.
The tendency for a metal to break at a point that is considerably below the ultimate tensile strength due to the conditions of repeated cyclic stressing and considerably below the ultimate tensile strength.
A metallurgical phase of iron having a body-centered cubic crystalline structure. Ferrite is soft, magnetic, and less susceptible to certain corrosion cracking than austenite.
A calculated value indicating the relative ability of a particular chemical composition of steel to form ferrite upon solidification from the molten state. The higher the ferrite number, the higher the percent of ferrite formed. Several different ferrite number formulas have been developed and should not be interchanged.
Ferritic Stainless Steel:
A magnetic grade of stainless steel having a microstructure consisting of ferrite, including some of the 200 and 400 series stainless steels. Hardness can be increased slightly by cold work, but not by heat treatment. At lower temperatures, ductility and formability is significantly less than that of austenitic grades. As the only major alloying element is chromium (10% to 30% depending on specific grade), these steels are relatively inexpensive to produce and are common in automotive exhaust and ornamental applications.
A test applied to tube involving a tapered expansion over a cone. Similar to a pin-expansion test.
The ease with which a metal can be shaped through plastic deformation. Evaluation of the formability of a metal involves measurement of strength, ductility, and the amount of deformation required to cause fracture.
A measurement of thickness. There are various standard gages, such as United States Standard Gage (USS), Galvanized Sheet Gage (GSG), and Birmingham Wire Gage (BWG).
Gas Tungsten Arc Welding (GTAW):
An arc welding process that uses an arc between a tungsten electrode (nonconsumable) and the weld pool (base metal of strip). A high quality full fusion weld is achieved. The process can be performed with or without the addition of filler material. The GTAW process is also commonly referred to as Tungsten Inert Gas (TIG) welding.
A measure of the size of individual metallic crystals usually expressed as an average. Grain size is reported as a number in accordance with procedures described in ASTM grain size specifications.
In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.
Resistance of metal to plastic deformation. Various hardness tests, such as Rockwell, Brinell, Vickers and Knoop, may be used.
Heat Exchanger Tube:
A tube for use in an apparatus in which fluid inside the tube will be heated or cooled by fluid outside the tube. The term usually is not applied to coiled tubes or to tubes for use in refrigerators or radiators.
An identifying number assigned to the product of one melting.
A combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition. See various types below.
Annealing is a heat treatment process that usually involves a relatively slow cooling after holding the material for some time at the annealing temperature. The purpose of the annealing treatment may include: (a) to induce softness; (b) to remove internal stresses; (c) to refine the grain size; (d) to modify physical and or mechanical properties; (e) to produce a definite microstructure; (f) to improve machinability. It is generally desirable to use more specific terms in describing the heat treatment to be used (for example, finish anneal, full anneal or medium anneal, as applicable).
Heat Treatment/Bright Anneal:
Carried out in a controlled furnace atmosphere, so that surface oxidation is reduced to a minimum and the tube surface remains relatively bright.
Heat Treatment/Dead Soft:
A heat treatment applied to achieve maximum softness and ductility.
Heat Treatment/Full Anneal:
Heating to a temperature above the upper critical and slow cooling below the lower critical.
Heat Treatment/Isothermal Anneal:
Austenitizing a heat treatable alloy and cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite-carbide aggregate.
Heating a ferrous metal to a temperature approximately 100 ˚F above the upper critical temperature and cooling in still air.
A process of rapid cooling from an elevated temperature by contact with liquids or gases.
Heat Treatment/Soft Anneal:
A high temperature stress relieving anneal usually performed in the temperature range of 1250 ˚F to 1350 ˚F. This type of anneal reduces hardness and strength of a cold worked steel to achieve near maximum softness.
Heat Treatment/Solution Anneal:
Heating steel into a temperature range wherein certain elements or compounds dissolve, followed by cooling at a rate sufficient to maintain these elements in solution at room temperature. The expression is normally applied to stainless and other special steels.
Heat Treatment/Spheroidizing Anneal:
A general term that refers to heat treatments that promote spheroidal or globular forms of carbide in carbon or alloy steels.
Heat Treatment/Stabilizing Anneal:
A treatment applied to austenitic stainless steels wherein carbides of various forms are deliberately precipitated. Sufficient additional time is provided at the elevated temperature to diffuse chromium into the areas adjacent to the carbides (usually grain boundaries). This treatment is intended to lessen the chance of intergranular corrosion.
Heat Treatment/Stress Relieving:
A heat treatment that reduces internal residual stresses that have been induced in metals by casting, quenching, welding, cold working, etc. The metal is soaked at a suitable temperature for a sufficient time to allow readjustment of stresses. The temperature of stress relieving is always below the transformation range. Finish anneal, medium anneal and soft anneal (sub-critical) describe specific types of stress relief anneals.
Heat-Affected Zone (Haz):
The portion of the base metal that was not melted during welding, but in which the microstructure and mechanical properties were altered by the heat.
High-Strength Low-Alloy (HSLA) Steels:
Steels designed to provide better mechanical properties and/or greater resistance to atmospheric corrosion than conventional carbon steels. They are not considered to be alloy steels in the normal sense because they are designed to meet specific mechanical properties rather than a chemical composition. Typical HSLA steels have minimum yield strengths 50 ksi, 60 ksi, 70 ksi or 80 ksi. The chemical composition of the specific HSLA steel may vary for different product thickness to meet mechanical property requirements. The HSLA steels have low carbon contents (0.05 to ~0.20% C) in order to produce adequate formability and weldability. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium and titanium are used in various combinations.
Hot Finished Seamless Tubing:
Tubing produced by rotary piercing, extrusion, and other hot working processes without subsequent cold finishing operations.
Hot Rolled ERW Tubing:
As welded electric resistance welded tubing made from hot rolled strip or sheet.
A corrosion test for stainless steels. The weight loss per unit area is measured after each of five 48-hour boils in 65% nitric acid (per ASTM A 262 Practice C). The test results are calculated to and reported as the average corrosive rate of the five boils in inches per month (1pm) corrosion rates. The test is used to determine the suitability of a material for nitric acid service. Since most of the weight loss is due to intergranular attack, the Huey test is commonly used as an indication of the resistance of a stainless steel to intergranular corrosion.
A test in which a liquid, usually water (under pressure), is used internally to detect and locate leaks in a tube of a fabricated structure.
Inside diameter of a tubular product. It is also known as the opening or bore of a tube or pipe.
A test to determine the energy absorbed in fracturing a test bar at high velocity. The typical test for tubing is a notch test, with an artificial notch present and tested at various temperatures.
When referring to the physical condition of a product, any departure of a quality characteristic from its intended level or state. When referring to the dimensional condition of a product, any dimensional characteristic that is out of intended range. The existence of an imperfection does not imply nonconformance, nor does it have any implication as to the usability of a product in service. An imperfection should be rated on a scale of severity, in accordance with applicable specifications, to establish whether or not the product is of acceptable quality.
A physical and mechanical discontinuity occurring within a metal product, usually consisting of nonmetallic foreign material. Inclusions are often capable of transmitting some structural stresses and energy fields, but to a noticeably different degree than from the parent material. The foreign particles are usually compounds, such as oxides, sulfides, silicates or combination of these.
Integral Finned Tubing:
Tubing with raised surface fins formed from the wall of the tube itself.
Corrosion that occurs at the grain boundaries in austenitic stainless steels that have been heated to and held at temperatures between 850 ˚F and 1450 ˚F.
ISO (International Organization For Standardization):
Organization that prepares specifications. Both Canada and the U.S.A. are ISO members and participate in ISO specification development.
Hardenability test performed on alloy steels to determine depth and degree of hardness resulting from a standard end-quenching method with cold water.
During the steel making process, as molten metal comes from the furnace, it contains more or less oxygen in the form of dissolved oxides, the amount varying with the composition desired and with certain conditions of steel making. If certain elements, such as manganese, silicon or aluminum are added in sufficient amounts to molten steel in the ladle, the metal will solidify quietly without evolution of gases. When processing rimmed steel and semi-killed steel, killed steel is one of the methods of deoxidizing. Killed steel is deoxidized with strong deoxidizing agent(s) to reduce the oxygen content to a minimum so that no reaction occurs between carbon and oxygen during solidification. Usually, killed steel has the best internal cleanliness condition.
A large vessel into which molten steel or molten slag is received and handled.
Chemical analysis obtained from a sample taken during the pouring of the steel.
Defects resulting from the presence of blisters, seams or foreign inclusions aligned parallel to the worked surface of a metal.
A surface defect caused from folding the surface of an ingot, bloom or bar during hot rolling operations and then rolling or forging the fold into the surface.
Laser Beam Welding (LBW):
A fusion joining process that produces coalescence of materials with the heat obtained from a concentrated beam of coherent, monochromatic light impinging on the joint to be welded. Generally an autogenous weld with no filler metal added.
A continuous strip of information that is printed with an inert ink along the longitudinal surface of the tube after final inspection. This data includes ASTM spec number, material identification, size and wall thickness, as well as a heat number identity. Full traceability is possible with any line-marked product.
A constituent in quenched steel formed without diffusion and only during rapid cooling below the martensitic start (Ms) temperature. Martensite is the hardest of the transformation products of austenite.
Mean Coefficient of Thermal Expansion:
This is the amount that a material will grow in size when subjected to a temperature rise. It is measured in inches/inch/F. This number multiplied by the length of the tubing (in inches) and by the temperature rise (in ˚F) indicates how much the tube length will expand (in inches). If the temperature decreases, the tube will shrink by a similar amount.
The properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example tensile strength, yield strength, elongation, hardness, and fatigue limit.
Used for a variety of mechanical and structural purposes, as opposed to pressure tubing, which is used to contain or conduct fluids or gases under pressure. It is used for the starting stock for machined or formed parts of industrial, automotive, agricultural, aircraft, transportation, material handling and household equipment. Mechanical tubing may be hot finished or cold drawn. It is commonly manufactured to consumer specifications covering chemical analysis and mechanical properties. It is made to exact OD and wall thickness dimensions and custom-produced to end-use applications in seamless and welded condition.
The science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by such tools as low-powered magnification, optical microscope, electron microscope and diffraction or X-ray techniques.
Any wall having tolerances specified all on the plus side.
Modulus of Elasticity:
A ratio of stress to strain used in engineering calculations to determine rigidity and deflections. The higher the number, the more rigid the item will be for a given load. The units are in pounds per square inch (psi).
Methods of detecting defects without destroying or permanently changing the material being tested. Test methods include ultrasonic, eddy current, magnetic particle, liquid, penetrant, and X-ray.
Outside diameter of a tubular product.
A circumferential, full fusion butt or girth weld used to join two lengths of tubing. It is a GTAW welding process similar in nature to the longitudinal weld seam of a welded tubular product.
The difference between the maximum and minimum outside diameters of any one cross section of a tube. It is a measure of deviation from roundness.
In its simplest terms, oxidation means the combination of any substance with oxygen. Scale developed during heat treatment is a form of oxidation.
A compound consisting of oxygen and one or more metallic elements.
The changing of the chemically active surface of a metal to a much less active state by the application of the proper chemical treatment or by applying an induced electrical current and voltage for cathodic or anodic protection from corrosion. An example of chemically passivating stainless steel would be to immerse it in a hot solution of approximately 10% to 20% by volume nitric acid and water.
Properties of a material that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, and magnetic permeability.
Use of solutions, usually acids, to remove surface oxides from a tube; may also be used to produce a desired surface finish.
Tubing produced for the purpose of containing or conducting fluids or gases under pressure. Pressure tubing is produced to exact diameters and decimal wall thicknesses to ASTM or ASME specifications for boiler, heat exchanger, condenser tubes, etc. Made using both seamless and welded processes in carbon, alloy, and stainless steels.
An instrument used for measuring surface finish.
Common engineering abbreviation for pounds per square inch. A measurement of stress in a material.
An instrument of any of various types used for measuring temperatures.
(1) Formation of a new, strain-free grain structure from that existing in cold worked metal, usually accomplished by heating (solution annealing of austenitic stainless steels).
(2) The change from one crystal structure to another, as occurs when heating or cooling through a critical temperature (as in the change of an as-welded dendritic structure to an equi-axed grain structure, similar to that of the parent material).
Reduction of Area:
A measure of ductility determined in a tensile test. It is the maximum reduction, at the fracture, of the cross section area of a specimen, as compared with its original cross section area.
Macroscopic stresses that are set up within a metal as the result of non-uniform plastic deformation. This deformation may be caused by cold working or by drastic gradients of temperature from quenching or welding.
Tubular product that is made by piercing or hot extrusion to form the tube hollows. Further reduction of the tube hollows is accomplished by cold drawing or tube reducing to the final finish and size. Initial billet or ingot is cast.
Steel that is incompletely deoxidized to permit the evolution of carbon monoxide, thereby offsetting solidification shrinkage.
Sensitization of stainless steel is a susceptibility to preferential grain boundary attack. Material that exhibits grain boundary carbide precipitation may or may not be sensitized.
A trade name given to alloy steel that is corrosion and heat resistant. The chief alloying elements are: chromium, nickel, and molybdenum. By AISI definition, a steel is called “stainless” when it contains 10.5% or more chromium.
Steel containing 10.5% or more chromium. Invented in 1903, metallurgists discovered that adding chromium to carbon steels imparted much improved corrosion resistance. Other major alloying elements include nickel, manganese, molybdenum, silicon and titanium.
Stress Corrosion Cracking:
Cracking of metals under combined action of temperature, corrosion and stress. The stress can be either applied or residual.
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