Pipe Glossary of Terms
AAR: Association of American Railroads.
Actual Pipe Size: The measurement equal to the outside diameter of the pipe.
Actual Size: The real measurement for either the Inside Diameter or the Outside Diameter of
Adapter: A fitting used to connect pipes of different materials that require different joining
methods; for example, a pipe which is threaded, connection to a tube that cannot be threaded.
AGA: American Gas Association.
Age Hardening: Heat treatment.
Aging: Heat treatment.
Air Hardening: Heat treatment.
Air Testing: Subjecting the specimen to air pressure.
AISI: American Iron and Steel Institute.
Alloy: A combination of two or more metals or a metal and a non-metal substance which is
heated until they are blended together to form a new material.
Alloy Group: A kind of stainless steel classified according to its major alloy content. For
example, the three main groups of stainless steel are the straight chromium group, the
chromium-nickel group and the chromium-nickel-manganese group.
AMS: Aerospace Materials Specification.
Annealing: A process involving heating and cooling usually applied to induce softening. Also
refers to treatments intended to alter mechanical or physical properties, produce a definite
micro-structure or remove gases.
ANSI: American National Standards Institute; the organization which sets the specifications for
API: American Petroleum Institute; the organization that sets standards for pipe used in the
ASA: American Standard Association, now ANSI; also the American Supply Association, an
association of member distributors that sell various products.
ASM: American Society for Metals.
ASME: American Society of Mechanical Engineers.
ASTM: American Society for Testing and Materials International.
As Drawn Tubing: Tubing that is non-heat treated, cold drawn and having a scale-free, cold
As Welded Cold Rolled Tubing: Tubing used for applications where superior surface is
required, as for plating. It has slightly closer wall and inside diameter tolerances in most sizes.
As Welded Hot Rolled Tubing: Tubing that is more economical for use in many applications
where surface finish and/or inside diameter tolerances are not as critical: may be supplied with
inside flash in, flash controlled to 0.010″ maximum, or flash controlled to 0.005″ maximum.
Atmospheric Corrosion: Rust; rust occurs when unprotected steel is exposed to air containing
moisture. The attack is generally uniform on plain surfaces and may be affected by corners and
Austenitic Grain Size: Indicates the grain structure established by a standardized heat
Austenitic Stainless Steel: A kind of stainless steel belonging to either the chromium-nickel
alloy group or the chromium-nickel-manganese alloy group.
AWWA: American Water Works Association.
Bales: Banded lifts of pipe.
Bark: The decarburized layer just beneath the scale that results from heating steel in an
Bar Mill: Rolling mill where blooms or billets form bars.
BDLS: Bundles; the practice of packaging pipe. Pieces per bundle vary by pipe size.
B.E.: Beveled end.
Beading: Raising or depressing a ridge of specified contour on a section of tubing.
Bearing Load: A compressive load supported by a member, usually a tube or collar, along a
line where contact is made with a pin, rivet, axle or shaft.
Bearing Strength: The maximum bearing load at failure divided by the effective bearing area
in a pinned or riveted joint; the effective area is calculated as the product of the diameter of the
hole and the thickness of the bearing member.
Bend Radius: The radius corresponding to the curvature of the bent specimen or bent area of
a formed part, measured on the inside of a bend or on the centerline of the tube, as defined.
Bends: Name used for cast iron soil pipe elbows; also an elbow, steel or other that changes
the flow by some degree.
Bend Tests: Tests used to determine the ductility and/or other characteristics of steel or
tubing. The number of bends and the radius and degree of bends are generally determined by
the applicable specifications.
Bevel: The angle formed between the prepared edge of the end of the pipe and a plane
perpendicular to the surface. The bevel used for standard line pipe is 30.
Beveled End: Description of pipe with its ends cut at an angle to facilitate the weld joint used to
join separate lengths of pipe.
Billet: Can be a round, solid bar of steel which will be pierced in the center to form a seamless
pipe or tube or a square or rectangular semi-finished form that can be used in the manufacture
of large diameter seamless tubes.
Black Bare: Term associated with the pipe surface whereby the pipe will not be coated with
mill spray oil; grease spots and cutting oils will not be removed.
Black Dry: Term associated with the pipe surface whereby the pipe will not be coated with mill
spray oil; all grease spots and cutting oils will be removed by washing.
Black Oiled: Black or Bare Steel Pipe that has been oil coated.
Black Steel Pipe: Steel Pipe that has been coated with a rust preventative to protect the pipe
during shipping and initial storage (sometimes called Plain Pipe or Black Iron).
Blind Flange: Type of flange made with no center hole that is bolted to another flange to end a
Blk. St. (or Bl. St.): Abbreviation used to indicate Black Steel Pipe; can be used simply to
designate pipe that has not been galvanized.
Bloom: A semi-finished hot rolled product produced on a blooming mill.
Blow Out: The phrase describing the removal of cut flash from tubing.
BOF: Basic Oxygen Furnace.
BOP: Basic Oxygen Process.
Borescope: An optical device used for inspecting the inside surface of tubes under low
Box Annealing: A process of annealing a ferrous alloy in a suitable closed metal container
with or without packing material in order to minimize oxidation. The charge is usually heated
slowly to a temperature just below the transformation range (but sometimes above it or within it)
and then cooled slowly. The process is also called Close Annealing or Pot Annealing.
Branch: An outlet or an inlet that is not in line with the run of the fitting.
Brazing: Joining metals by fusion of non-ferrous alloys that have melting points above 800 F
but lower than the metals being joined. This may be accomplished using a torch (torch brazing),
in a furnace (furnace brazing), or by dipping in a molten flux bath (dip or flux brazing). The filler
material is usually in rod form for torch brazing; in furnace and dip brazing, the work material is
first assembled and the filler metal may then be applied as wire, washers, clips, bands or may
be integrally bonded as in brazing sheet.
Briggs Standard: A standard of thread dimensions; it is the same as the American Standard.
Bright Annealing: A process of annealing usually carried out in a controlled furnace
atmosphere so that surface oxidation is reduced to a minimum and the surface remains
Brinnell Hardness Test: A test for determining the hardness of a material by forcing a hard
steel or carbide ball of specified diameter into it under a specified load.
Brittleness: A tendency to fracture without appreciable deformation.
BTU: British Thermal Unit; a measure of heat.
Building Drain: The lowest section of horizontal piping in a plumbing drainage system that
receives the discharge from both the waste and soil lines and conducts it to the sewer outside
the wall of the building.
Bull Tee: A tee fitting on which the diameter of the branch opening is larger than the diameter
of the run openings.
Bundles (BLDS): Method of shipping standard pipe that is 4″ or less in diameter. Weight and
number of pieces can be different with each pipe size.
Burnishing: Plastic smearing such as may occur on metallic surfaces during buffing.
Burr: A rough or sharp edge left on metal by a cutting tool.
Burst Test: A destructive hydraulic test to determine actual yield strength and ultimate strength
of welded pipe and seamless pipe.
Bushing: A straight line fitting that connects a pipe having male pipe threads to a female pipe
of larger diameter.
Butt Weld: A weld which is formed when two beveled pipe ends or a beveled pipe end and a
beveled fitting with the same diameter and wall thickness are permanently welded together.
BW: Butt Weld Pipe; the same as Continuous Furnace Weld Pipe where the strip edges are
heated and forced together.
BWG: Birmingham Wire Gauge.
Camber: A deviation from edge straightness usually referring to the greatest deviation of side
edge from a straight line.
Canning: A dished distortion in a flat or nearly flat surface; sometimes referred to as oil
Cap: A fitting, into which the end of a pipe is attached for the purpose of closing the end of a
Capped Steel: A variation of rimmed steel that is cast in a bottle top mold. The cap is placed in
the neck of the mold soon after the mold has been filled to the proper level stopping the rimming
action before it is completed by cooling the top metal. This produces an ingot having a thin rim
relatively free of blowholes and with less segregation than is usual for a rimmed ingot of the
Carbide: A compound of carbon with one or more metallic elements.
Carbide Precipitation: A process in which carbon and chromium atoms combine when certain
kinds of stainless steel are exposed to high temperatures. Chromium carbide grains are formed
which separate from the steel. This separation causes the area to lose its corrosion resistance
because of lack of chromium. Carbide Precipitation is also called “sensitization” and
Carbon Steel: Carbon Steel is steel that owes its properties chiefly to various percentages of
carbon without substantial amounts of other alloying elements; also called Plain Carbon or
Straight Carbon Steel.
Carbonitriding: A process in which a ferrous alloy is case-hardened by first being heated in a
gaseous atmosphere of such composition that the alloy absorbs carbon and nitrogen
simultaneously, then being cooled at a rate that will produce the desired properties.
Carburizing: To introduce carbon by adding carbonaceous material such as coke, coal,
electrode scrap, etc to molten steel, or by heating solid steel while it is in contact with the
Case Hardening: A process of hardening a ferrous alloy so that the surface layer is made
substantially harder than the interior or core. Typical case-hardening processes are carburizing
and quenching, cyaniding, carbonitriding, nitriding, induction hardening and flame hardening.
Casing: Pipe used as a structural retainer for the exterior walls of water, gas, oil well, or other
application; also used as a structural interior retainer for another pipe commonly seen in oilfield
CBW: An outdated term identifying Continuous Furnace Weld tubing or pipe.
CD: Cold drawn; drawing pipe or tubing through a die to reduce diameter and wall, to obtain
closer tolerances, a better finish, or higher physical properties.
Centerless Grinding: A method of grinding unmounted cylindrical surfaces.
Chamfer: A beveled surface to eliminate an otherwise sharp corner; a finishing operation prior
to threading usually in the interior of the end of pipe.
Charpy Impact Test: See Impact Testing.
Charpy 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.
Check Analysis: An analysis of the metal after it has been rolled or forged into semi-finished
or finished forms. It is not a check of the ladle analysis, but is a check against the chemistry
Chemical Properties: Normally associated with a limited number of chemical elements;
minimum or maximum limits are established in most ASTM and API specifications.
Chipping: A method for removing seams and other surface defects with chisel or gouge so that
such defects will not be worked into the finished product. Chipping is also often employed to
remove metal that is excessive but not defective. Removing defects by gas cutting is called
deseaming or scarfing.
Chromium: An alloying element added to alloy steel in amounts to about 1.50% to increase
hardenability. Chromium content in excess 5.0% confers special ability to resist corrosion.Steels containing more than 10.5% chromium are called Stainless Steel.
Chromium-Nickel (Cr-Ni) Group: A kind of austenitic stainless steel sometimes used in the
piping industry that contains chromium and nickel as its major alloys.
Chromium-Nickel-Manganese Group: A kind of austenitic stainless steel commonly used in
the piping industry that contains chromium, nickel and manganese as its major alloys.
Chucking: A method of mechanically securing material to be machined.
CL: Cut Length, pipe cut to a specific ordered length.
Cladded Racks: Storage racks for stainless steel that are made from iron with strips of
stainless steel running perpendicular to the iron.
Cladding: A process of covering one metal with another and generally establishing a
metallurgical bond between them.
Clean-Out Plug: A metallic plug or cover joined with a screw thread (plug) to an opening at the
bottom of a P-Trap that can be removed so that the trap can be drained.
Cleanup: The amount of metal removal required to obtain desired dimensions and complete
removal of inherent surface imperfections.
Cleanup Allowance: The amount that must be added to the finished OD dimension or
subtracted from the finished ID dimension to provide for the elimination of surface imperfections.
Close Nipple: A piece of pipe on which male pipe threads totally cover the surface (all thread);
usually the shortest length nipple.
Coated Tubing: A special coated tubing available from certain suppliers. This special product
is produced from pre-coated, flat rolled steel, or the coating may be applied to the tube in-line
immediately after welding. The weld zone of pre-coated material may be remetallized
immediately after welding. Either galvanized or aluminum coatings are available and provide
extra corrosion protection. The coating is an excellent base for a long lasting painted surface.
Coating: The process of covering steel with another material primarily for corrosion resistance.
Coatings, Types Of
Due to various customer preferences and methods of storage before use, many pressure or
mechanical tubing specifications do not indicate the type of protective coating for tube orders. Many types of proprietary coatings are available, but individual producers usually have a
standard type most suitable to their operations and equipment, and to the preference and
experience of their major customers. The following definitions are commonly accepted and
practiced in the industry.
- Dry: Indicates absolutely no oil coating. This may involve special processing or removal
of processing oils. Since such tubes have no protective coating, they are susceptible to
rapid rusting during transit and storage.
- No Oil: There is no intentional application of oil. A light coating of processing oil in the
tubes gives limited protection against rust.
- Slushing Oil: Indicates a specific oil coating application. Several types and numerous
variations exist within this category, as well as different methods of application. Some
- Light Petroleum Oil: Tubes dipped or sprayed. The oil never dries and tubes remain
oily throughout storage. Normal cleaning methods will remove the oil.
- Water Soluble Oil: Usually a dipping application precedes a drying period that permits
evaporation of the water. This leaves a light oily or waxy film on the tubes. Normal
cleaning methods will remove the oil or film.
- Solvent Cut Back Oil: Tubes may be dipped or sprayed. Coating consists of oil or wax
dissolved in petroleum solvent. When the solvent evaporates, a light, oily, or waxy film
remains. Some formulations leave a heavier coating for specialized protection, and
again, normal cleaning methods will remove the coatings.
- Pipe Oil: Similar to a varnish, this consists of resins dissolved in a solvent. It usually
involves spraying or swabbing the outside of tubes intended for watertube boilers. It is
difficult to remove by normal cleaning solutions and should not be applied to water side
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.
Cold Drawing: The process of pulling a tube through a hardened steel or carbide die to reduce
its diameter and obtain closer O.D. tolerances. Process can also be carried out by pulling the
tube over a mandrel as it progresses through the die, thereby more closely controlling inside
diameter. Higher tensile properties are obtained because the operation is performed at room
temperature or in isolated cases at elevated temperatures, but considerably under the lower
Cold Drawn: Refers to tubing drawn in the cold state through a hardened steel or carbide die,
either with or without a mandrel on the inside.
Cold Heading: Cold heading consists of forcing metal to flow cold into dies to form thicker
sections and more or less intricate shapes. The operation is pre-formed with specialized
machines where the metal, in the form of wire or bar stock, may be upset or headed in certain
sections to a larger size and, if desired, may be extruded in other sections to a smaller diameter
than the stock wire. Although cold heading was developed for the production of bolts, screws
and rivets and is used largely for these parts, the process is applicable to a wide variety of
special parts that have somewhat similar form.
Cold Reduction: The reduction of sectional dimensions of a tube by any of a number of types
of cold-working operations.
Cold Rolled Sheet: Hot rolled steel sheet cold reduced to obtain lighter gauges and better
surface finish than hot rolled sheet products.
Cold Rolled Strip: A special narrow steel that is produced to restricted surfaces, edges and
tempers. It is not the same as slit cold rolled sheet.
Cold Sinking: Similar to cold drawing, except that the tube is drawn through a die, but without
an internal mandrel. Usually used only for making heavy wall or small tubing, where drawing
over a mandrel is impractical. Only outside diameter is closely controlled.
Cold Straightening: This process is used to achieve straightness tolerances by deflecting the
product until plastic deformation occurs. Cold straightening may be achieved either on rotary
straightening equipment or by press straightening.
Cold Work: Plastic deformation at such temperatures and rates that substantial increases
occur in the strength and hardness of the metal. Visible structural changes include changes in
grain shape and, in some instances, mechanical twinning or banding.
Cold Working: Deforming a metal plastically at such a temperature and rate that strain
hardening occurs. The upper limit of temperature for this process is the re-crystallization
Collapsing Pressure: A pressure that, when applied to the outside of a tube, causes it to cave
in or to fail by bending or buckling inwardly.
Columbium: A metal that is added to steels to increase their strength after hot rolling through
precipitation of carbides, one of several typical additives for high strength-low alloy or microalloyed
Commercial Quality (CQ): Sheet of this quality is for uses involving simple bending or
moderate drawing. Commercial Quality sheet can be bent flat upon itself in any direction at
room temperature. (Sheets of this quality can be specified to ASTM A526.)
Commercial Quality Tubing: A term used to describe tubing that may be used as received for
many applications. It is generally produced to the buyer’s wall thicknesses, OD and ID
tolerances as well as to the buyer’s mechanical properties.
Companion Flange: One of a pair of flanges designed to be bolted together to form a flange
Compression Test (Tubing): Test made on a section of tube applying compressive force
perpendicular to the diameter of the tube; also called Crush Test.
Con Cast: Continuous Cast.
Concentric Reducer (Concentric Reducing Coupling): A fitting used to connect one pipe
with another of a smaller diameter such that the centers of the run openings are in line.
Concentricity: Concentricity is the relationship between the center of the inside diameter and
the center of the outside diameter. Concentricity is related to the variation in the wall thickness
of any one circumference of a tube.
Conditioning: The removal of surface defects (seams, laps, pits, etc.) from steel. Conditioning
is usually done when the steel is in semi-finished condition (bloom, billet, slab). It may be
accomplished, after an inspection, by shipping, scarfing, grinding, or machining.
Conduit: Pipe serving as a duct for electrical wiring; usually supplied in ten-foot lengths, with
plain ends or threaded and coupled. The pipe used is normally galvanized, slightly larger than
standard weight with a smooth inner surface. However, the term conduit may refer to pipe for
uses other than electrical.
Constant-Load Test: A stress-corrosion-cracking or mechanical test in which the specimen is
stressed by applying a dead load.
Continuous Casting: A casting technique in which a slab or billet, or other shape is
continuously solidified while it is being poured, so that its length is not determined by mold
Continuous Weld (CW) or Continuous Buttweld (CBW): In contrast to the ERW system the
steel is formed into a tubular shape while the steel is hot. When they meet, the edges are fused
or welded together and no additional weld material is necessary.
Controlled Cooling: A process of cooling from an elevated temperature in a pre-determined
manner, to avoid hardening, cracking or internal damage, or to produce a desired
microstructure. This cooling usually follows the final hot forming operation.
Cooling Stresses: Stresses developed by uneven contraction of external constraint of metal
during cooling: also those stresses resulting from localized plastic deformation during cooling,
Corrosion: Gradual chemical or electrochemical attack on a metal by atmosphere, moisture or
Corrosion Fatigue: The repeated cyclic stressing of a metal in a corrosive medium, resulting
in more rapid deterioration of properties than would be encountered as a result of either cyclic
stressing or of corrosion alone.
Coupling (CPLG): An internal threaded sleeve used to connect two pipes, fittings, or valves in
a straight line of the same size.
Creep: The long term deformation of metals under a constant load or a constant stress, usually
at elevated temperatures. Load stress times are generally in excess of I00,000 hours before
Creep Strength: The constant nominal stress that will cause a specified quantity of creep in a
given time at a constant temperature. It is a measure of a tube’s ability to withstand prolonged
stress or load without significant continuous deformation. In steels it is an important factor only
at elevated temperatures.
Critical Strain: The percentage strain or amount of cold work at which large grain growth
occurs during annealing at a specific temperature.
Crop: The end or ends of a piece of pipe that contain the defects to be cut off and discarded;
also termed crop end and discard.
Cross Tee: A fitting used to connect four pipes at right angles; also called a double tee.
Cross Y: A fitting to join two branch lines to the main run at 45° angles; also called double
Crown: Crown, in plates, sheet or strips, is characterized by a greater thickness in the middle
than at the edges. It may be caused by a deflecting (bending) of the rolls or by worn rolls.
Crush Test: Same as Compression Test.
CS: Carbon Steel.
Cup Fracture: The type of fracture in which the exterior portion is extended and the interior is
relatively depressed, resembling a cup. This type of fracture is a good indication of a ductile
material. When only a part of the exterior is extended, the term half-cupped or quarter-cupped
Cut Off: This operation is used primarily to:
- Cut the tubing to the length required by the customer.
- Obtain metallurgical samples to provide material for testing required by the customer’s
Cut Length: 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.
CW: Continuous Weld.
CWT: Per hundred weight.
Diameter: The distance between one edge of a circle and the other as measured on a straight
line through the center of the circle.
Die Stamping: Permanent marking impregnated on pipe as required in some specifications.
- Dimensions of Tubing:(The dimensions for tubing should not be confused with the nominal
dimensions for pipe that are standardized and set by the applicable specifications.)
• A round tube section has three dimensions, any two of which may be varied. The three
dimensions are outside diameter (OD), inside diameter (ID), and wall thickness or
- OD: Outside Diameter; Specified in inches and fractions of an inch, or in inches and
decimals of an inch.
- ID: Inside Diameter; Specified in same terms as the OD.
- Wall: Thickness or Gauge Specified in either fractions of an inch, decimals of an
inch, or by a “Wire Gauge” number. In the United States, the standard wire gauge
used for tubing is the “Birmingham” iron wire gauge, designated Bwg. or B.W.G.
- 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
- Maximum and Minimum referring to the greatest and least values of any dimension as
agreed upon, constitute the limits within which all such dimensions must fall.
- Average dimensions are those secured by averaging a series of micrometer readings of
sufficient number to assure that all parts of the tube are within the maximum and
minimum dimensions specified.
Dimpling: Occurs when tubing is punch cut. A depression is formed by the cutting operation.
‘DIN’: Indicates a foreign specification (German), usually in metrics.
DOM: Drawn over Mandrel. (A cold working process) See Mandrel drawn for explanation.
Double Extra Heavy (Strong): (Dble E.H. or XXH): Refers to the heaviest weight steel pipe,
that has the thickest wall measurement, that is scheduled available from NPS 1/8 to NPS 8. Such pipe is also called Double Extra Strong (XXS or Dble XS).
Double Random Length (DRL): Pipe shipped in different lengths generally greater than 30′
and less than 50′.
Double Tee: See Cross Tee.
Drain, Waste, and Vent Piping System: An assembly of pipe, fittings and valves used to bring
solid, liquid and gas wastes out of a building. This is also called a sanitary system.
- Forming parts by causing the plastic flow of metal in dies.
- Reducing cross section of tubing by pulling it through a die.
- Another term for tempering.
Drawing Quality Sheet and Bands (DQ): Drawing Quality Sheet and Bands are more ductile
and more uniform in chemical composition than CQ material. Some DQ sheet may be subject to
some loss of ductility with time. DQ material is produced from specially selected steel and
carefully processed to result in more-uniform drawing properties than CQ material. Hot rolled
DQ sheet and bands are used to make parts that are too difficult for the forming properties of
hot rolled CQ sheet and bands. Drawing Quality sheet and bands are subject to coil breaks,
sketcher strains and fluting in the as-rolled condition. If DQ sheet is to remain essentially free of
stretcher strains through fabrication, it should be roller leveled by the customer before forming.
Drawing Quality Special Killed Sheet and Bands (DQSK): Drawing Quality Special Killed
sheet and bands are rolled from aluminum-killed steel produced by special steelmaking and
processing practices. Sheet and bands have forming characteristics superior to CQ and DQ
sheet and bands. These characteristics make it excellent for use in severe drawing operations. It is recommended for processes in which delays between draws would detrimentally affect the
drawing performance of CQ and DQ materials. There is no loss of ductility with time.
Drifted: Attaining a certain minimum ID clearance by pushing or pulling a mandrel (pig) through
a pipe or tubing.
Drive Pipe: Electric Resistance Weld or Seamless Pipe with specially threaded ends to
promote a tight joint with the coupling; used for driving into the ground in water well applications.
Driven Well Pipe: Welded or Seamless galvanized standard weight pipe, usually threaded and
DSAW: See Double Submerged Arc Weld.
DRL: See Double Random Length.
Ductility: The ability of a material to deform plastically without fracturing; measured by
elongation in a tensile test.
DWV: Drain, Waste, and Vent.
Dye Penetrant Inspection: Non-destructive test employing dye or fluorescent chemical, and
sometimes, black light, to detect surface defects.
Eccentric Reducer (Eccentric Reducing Coupling): A fitting used to connect one pipe with
another of smaller diameter such that the centers of the run openings are not in line.
Eccentricity: The displacement of the I.D. of the tube with respect to the O.D. of the tube. Eccentricity results in the variation of wall thickness generally found in seamless tubing.
Eddy Current: Non-destructive testing method using eddy (DC electrical current) current flow
for the purpose of recognizing a discontinuity in the piece being tested.
18-8 Stainless Steel: A term used to refer to the 300 series austenitic stainless steel alloys in
which the basic formula is 18% chromium and 8% nickel.
Elastic Deformation: Temporary changes in dimensions caused by stress. The material
returns to its original dimensions after removal of the stress.
Elastic Limit: 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.
Elbow: A fitting designed to change the direction of a run by joining pipe or tube at an angle.
Electric Furnace (EF): a method to produce steel, basically from scrap metal.
Electric Resistance Weld: A method of manufacturing steel pipe in which a flat ribbon of steel
is cold-formed by rolls; electrical current is then used to weld the edges together. This pipe can
be normally produced in sizes from NPS 1/8 through NPS 26.
ELL: See Elbow.
Elongation: 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, as 25% in 2 inches.
Elongation may also refer to the amount of extension at any stage in any process that elongates
a body continuously, as in rolling.
Endurance Limit: The maximum stress that a metal will withstand without failure during a
specified number of cycles of stress. If the term is employed without qualification, the cycles of
stress are usually such as to produce complete reversal of flexural stress.
Erosion: The abrasion of metal or other material by liquid or gas, usually accelerated by
pressure of solid particles of matter in suspension, and sometimes by corrosion.
ERW: Electric Resistance Weld.
Etch Tests: Tests used to detect inclusions in steel. A common method of making such tests is
to dip the sample into acid that reacts with the inclusions and discloses their presence. See
EUE: External Upset Ends; used in API tubing and drill pipe.
Expanded Pipe: Pipe which has been enlarged circumferentially by mechanical or hydraulic
Extra Strong: Extra Heavy.
Extra Heavy: A reference to pipe with thicker than standard walls, thus heavier than standard
weight; sometimes called Extra Strong (may be abbreviated as EH, XH, ES, or XS). In pipe
sized from NPS 1/8 through NPS 8 Extra Heavy is the same as “Schedule 80”.
Extrusion: Production process in which steel is forced by compression through a die into solids
(round or special shape) or through a die and over a mandrel to form a tubular shape. See
Seamless Section for details.
Face Bushing: A bushing with no hex head.
Fatigue: The tendency for a metal to break under conditions of repeated cyclic stressing;
stresses that are considerably below the ultimate tensile strength.
Fatigue Limit: The maximum stress that a metal will withstand without failure for a specified
FED: Prefix for US government specifications, most of which are now cancelled.
Female Pipe Threads (FPT): Threads that occur on the inside surface of a pipe or a fitting.
Ferritic Stainless Steel: A type of straight chromium stainless steel.
Ferroalloy: An iron-bearing product, not within the range of those called steels, which contains
a considerable amount of one or more alloying elements, such as manganese, silicon,
phosphorus, vanadium, chromium. Some of the more common ones are ferrochromium,
ferromanganese, ferrophosphorus, ferrosilicon, ferrovanadium. The chief use of these alloys is
for making additions of their respective alloying element to molten steel.
Ferrous Metal: Metal that contains iron.
Ferrous Metallurgy: That branch of metallurgy dealing with iron and steels.
Finish: In the tubing/pipe industry, refers to the type of surface and end condition desired or
existing in the finished product.
Finish Anneal: See Heat Treatment.
Finish Machine: Size normally specified in terms of the maximum machined OD and the
minimum machined ID for tubular parts. Finish machine size represents the size of the part as it
comes from the final machining operation. From this size, the manufacturer can calculate a tube
size that will be guaranteed to be achieved upon final cleanup.
Finished Steel: Steel that is ready for the market without further work or treatment. Blooms,
billets, slabs, sheet bars, and wire rods are termed semi-finished.
Finishing Temperature: The temperature where hot mechanical working of metal is
Fitting: A part of a pipeline other than straight pipe or valves. Used to connect two pieces of
pipe, divert the direction of the flow, or stop the flow through the pipe. Fittings can join pipe so
the flow continues in a straight line, changes direction, pipe size is reduced or increased, or, a
fitting may be used to cap or plug the end of a pipe to stop the flow.
Fitting Ell: See Street Ell.
Fixtures: Devices such as sinks, showers or toilets that demand and hold water from a
- Severing a piece of steel by burning a portion out by means of an oxyacetylene torch, or
- Removing a part of the surface by means of a burning torch, as in conditioning; more
properly called scarfing.
Flame Hardening: A process of hardening a ferrous alloy by heating it with a high temperature
flame above the transformation range and then cooling as required.
Flange: The annular projection formed at right angles to the tube. As a test, used to evaluate
tube weld quality and overall soundness. Used in testing the tube and for Van Stone joints. Also
a fitting attached to the end of a piece of pipe used to attach a valve or other fitting.
Flanged End: In a flanged end, the tube has been belled or expanded and a flange turned over
until the wall of the tube end is at right angles to the wall of the tube. Also a fitting attached to
the end of a piece of pipe used to attach a valve or other fitting.
Flanged Joint: A joint formed when a flange is attached to the end of each pipe to be joined
and the flanges are bolted together with a gasket between them.
Flange Test: See Mechanical or Destructive Testing in the SMLS-CW-ERW sections.
Flange Union: See Flanged Joint.
Flare Test: The tapered expansion of a welded tube over a cone having various degrees and
Flaring Test: See Mechanical or Destructive Testing in the SMLS-CW-ERW sections.
Flash: A thin fin of metal formed at the sides of a forging or weld when a small portion of metal
is forced out between the edges of the forging or welding dies.
Flash Condition: When the edges of the tubing are brought to fusion temperature, side rolls
exert sufficient pressure to press the heated edges together, forming a welded joint. A small
amount of metal is extruded to the OD and ID of the tube commonly called the flash. No foreign
or additional metal is added in this operation. The extruded metal on the outside is always
removed to form a smooth outside surface. Occurs as part of the ERW method of manufacturing
Flash Controlled .005″ and .010″: This term means that the inside flash is controlled to the
limits shown. This is usually required where the customer telescopes one size into another,
uses a mandrel in fabrication, or is inserting something inside the tube or when the extruded
internal seam cannot be physically removed.
Flash-In Tubing: Tubing with the welding flash left on the inside of the tubing.
Flash Removed: From either or both OD and ID.
Flat Rolled Product(s): Basically a mill terminology for hot rolled bands and sheets, cold rolled
sheets, hot rolled plates, either in coil form or flat and, cut-to-length product.
Flattening Test: A test for either or both the tube base metal and weld line where a ring from
the tube or crop end is flattened. The weld line is positioned 0º or 90º to the applied force and
the ring flattened to a specified height. Examination is made during the test for signs of cracking.
Floating Plug: A plug that locates itself inside a tube during drawing, in such a way that the
tube is reduced in thickness between the plug and the die.
Flux Leakage: A testing method that magnetizes a tube and reads the magnetic lines of flux
that flow unimpeded around the wall and through its full thickness. If anything impedes this flow,
the lines of flux are diverted to both sides of the imperfection and if large enough, some of the
flow actually leaks out of the test product. With proper electronic instruments, it’s possible to
detect these flux leakages and evaluate the severity and location of the discontinuity in the tube
wall, whether OD, ID or internal.
F.O.B.: Free on Board.
Fog Quenching: A method of quenching in which a fine water vapor water or mist is used as
the quenching medium.
Forging: Used as a general term to describe the rolling, pressing or hammering of steel that
displaces the metal under compression by a locally applied force, usually at hot working
Forming: To shape or fashion with the hand or tools or by a shape or mold.
Forming Properties: Those physical and mechanical properties that allow a steel to be formed
without injury to the steel in the finished product.
FPT: Abbreviation for Female Pipe Threads.
Fracture Stress: The maximum principal true stress (fracture load divided by fracture area).
Fracture Test: Breaking a piece of metal for the purpose of examining the fractured surface to
determine the structure or carbon content of the metal or to detect the presence of internal
Free Machining: Pertains to the machining characteristics of a steel to which an ingredient has
been introduced that results in small broken chips, lower power consumption, better surface
finish, and longer tool life. Among such additions are sulphur or lead to steel, lead to brass, lead
and bismuth to aluminum, and sulphur or selenium to stainless steel.
Full Annealing: A softening process in which a ferrous alloy is heated to a temperature above
the transformation range, and after being held for a sufficient time at this temperature, is cooled
slowly to a temperature below the transformation range. The alloy is ordinarily allowed to cool
slowly in the furnace, although it may be removed and cooled in some other medium which
insures a slow rate of cooling.
Gage Length: Standard reference marks placed on a tensile test, customarily two inches apart
to determine percent elongation when stretched.
Gal. St.: Galvanized Steel.
Galvanic Action: The destruction of metal caused by an electrical current that forms when two
different metals touch each other while moisture is present.
Galvanic Corrosion: Type of corrosion caused when an electric current is generated between
two unlike metals and is then carried by the fluid into the pipe.
Galvanized Steel Pipe: Steel pipe that has been given a hot zinc coating; the zinc coating
protects the pipe from abrasive and corrosive materials, and from rust.
Galvanizing (GALV): The process of applying a coating of zinc to steel. This zinc coating is
applied by either the hot dip method or electrolytic deposition.
Galvannealed: Is a galvanized sheet steel that is altered by heat treatments or other
processes immediately after coating, before zinc solidifies. The coating produced consists of an
iron-zinc alloy and has a rougher appearance than the surface of regular coating. Sheets
produced in this manner are dull gray in color, have no spangle, and after proper preparation
can be painted.
Gauge (Gage is also correct spelling): A measurement of thickness. There are various
standard gauges such as United States Standard Gauge (USS), Galvanized Sheet Gauge
(GSG), Birmingham Wire Gauge (BWG, Bwg. or B.W.G.). The Birmingham Wire Gauge is
commonly used by the welded tube industry.
Girth Weld: A mid-length weld to connect two or more lengths of pipe; also called a mid weld.
Grade A or B: Designations used to indicate minimum yield and tensile strengths of steel in
seamless and welded pipe.
Grade: A class of steel defining amongst others, chemistry, tensile strength, and yield strength
Grain Size: The average size of the individual crystals in metals expressed as:
- The ASTM grain size number,
- The austinetics grain size,
- The number of grains per unit area as viewed metallographically or
- Some average dimensional value of the grains.
Grain Size (austenitic): Which is usually measured by the McQuaid-Ehn method, represents
the austenitic grain size of a material at a prescribed temperature.
Grains: Individual crystals in metals.
Grooved End Pipe: Steel Pipe with one or two narrow channels (grooves) either cut or rolled
into the end of a pipe. A special mechanical coupling assembly, that includes a gasket, is used
to make the joint.
Gross Ton (GT): 2240 pounds.
Gun Metal Finish: Welded tubing normalized, annealed, or stress relieved in a controlled
atmosphere furnace that exhibits a gun metal finish.
Hanger: A device used to support pipe in a system to prevent sag, sway and other undesired
Hardenability: The property in steel that determines the depth and distribution of hardness
induced by cooling from a suitable elevated temperature. The depth of hardness can vary with
the cooling rate.
Hardness: A mechanical property of metals related to tensile strength. Hardness is usually
expressed in terms of the method of measurement, such as:
- The resistance to penetration or indentation as measured by the Rockwell, Brinnell,
Vickers, and Knoop tests.
- Stiffness of temper of wrought products.
- Machinability characteristics.
Hardness Test: See Mechanical or Destructive Testing.
Heat Analysis: The term applied to the chemical analysis representative of a heat or blow of
steel and is the analysis reported to the purchaser. It is determined by analyzing (for such
elements as specified) a test ingot sample obtained from part of the heat or blow during the
pouring of the steel from a ladle.
Heat Treatment: 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.
- Age Hardening: Hardening by aging, usually after rapid cooling or cold working. Hardening is a result of a precipitation process, often submicroscopic, that occurs when
a super-saturated solid solution is naturally aged at atmospheric temperature or
artificially aged in some specific range of elevated temperature. Aging occurs more
rapidly at higher temperatures. (Synonymous with precipitation hardening.)
- Air Hardening: Heating a suitable grade of steel with high hardenability above the
critical temperature range and then cooling in air for the purpose of hardening.
- Annealing: Annealing is a heat treatment process that usually involves slow cooling
after holding the material for some time at the annealing temperature. The purpose of
the annealing treatment may be to induce softness, to remove internal stresses, to refine
the grain size, to modify physical and/or mechanical properties, to produce a definite
microstructure or to improve machinability.
- 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.
- Dead Soft: A heat treatment applied to achieve maximum softness and ductility.
- Finish Anneal: Heating of cold-worked tubing to a temperature below the lower critical
temperature usually 950°. Generally this treatment will relieve peak stresses without
substantially altering hardness.
- Full Anneal: Heating to a temperature above the upper critical level and slow cooling
below the lower critical level.
- Isothermal Anneal: Austenitizing a heat treatable alloy and holding at a temperature at
which austenite transforms to a relatively soft ferrite-carbide aggregate.
- Medium Anneal: Subjecting tubing to a subcritical temperature to obtain specific
- Normalize: Normalizing is a process that consists of heating to a temperature
approximately 1600ºF above the upper critical temperature and cooling in still air.
- Quenching: A process of rapid cooling from an elevated temperature, by contact with
liquids or gases.
- Soft Anneal: A high temperature stress relieving anneal usually performed in the
temperature range of 1250º to 1350ºF. This anneal reduces hardness and strength of a
cold worked steel to achieve near maximum softness.
- 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.
- Spheroidizing Anneal: A general term that refers to heat treatments that promote
spheroidal or globular forms of carbide in carbon or alloy steels.
- 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
- 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
- Tempering: Reheating quenched or normalized steel to a temperature below the
transformation range (lower critical) followed by any desired rate of cooling.
Heel Inlet: An inlet on the back of an ell fitting.
Hex Head Bushing: A bushing with a hex head at the end of the male pipe threads and at the
beginning of the female thread.
High Frequency Welding: A technique employed in the manufacture of electric resistance
weld pipe, typically 450 kilohertz and higher.
High Heel Inlet: An inlet on the back and near the top of an ell fitting.
High Strength Steel: Commonly known as High Strength-Low Alloy (HSLA), a specific class of
low alloy steels in which increased mechanical properties and, usually, good resistance to
atmospheric corrosion are obtained with moderate amounts of one or more alloying elements
other than carbon. One can also achieve high strength through physical (not chemical
Holiday: A discontinuity in the coating applied to a pipe’s surface.
Homogeneous: Usually defined as having identical characteristics throughout. However,
physical homogeneity may require only an identity of lattice type commonality throughout while
chemical homogeneity requires uniform distribution of alloying elements.
Homogenizing Treatment: A heat treatment, usually for a long time at a high temperature,
designed to make metal chemically homogeneous.
Honing: Honing is used to modify the inside surface of tubing used for hydraulic cylinders to
meet the cylinder manufacturers’ requirements for surface finish (micro-inch) and ovality. The
process uses honing stones, held on a rotating shaft. The honing head is passed through the
tube ID in a helical pattern. Honing pressure, stone grit and number of passes control the final
ID dimensions of the tubing.
Hot Extrusion: See Methods of Manufacturing Section.
Hot Finished Seamless Tubing: Tubing produced by rotary piercing, extrusion, and other hot
working processes without subsequent cold finishing operations.
Hot Forming: Working operations, such as bending and drawing sheet and plate, forging,
pressing, and heading, performed on metal heated to temperatures above’ room temperature.
Hot Quenching: A process of quenching in a medium at a temperature substantially higher
than atmospheric temperature.
Hot Rolled Coiled Bands and Sheets: The majority of welded pipe and tubing is produced
from coiled (HR) bands and sheets. Understand that HR Sheets and HR Bands are basically the
same product. Thus, the type of tube, specification, method of manufacture, etc. dictates to the
supplier whether HR bands or HR sheets are used. The term hot rolled bands is being
replaced at least in mill terminology with an unprocessed HR sheet. It is described as a hot
rolled, coiled product: not pickled, not oiled, not temper rolled, not side trimmed, and not
cropped back to gage. The product is produced to a specified nominal thickness and is sold on
an actual weight basis.
Hot Rolled ERW Tubing: Electric resistance tubing made from hot rolled strip or sheet.
Hot Shortness: Brittleness in hot metal.
Hot Stamp: Permanent marking placed (stamped) onto pipe as applied by manufacturer or
established by specification.
Hot Strength Reduced: A process that is utilized to obtain tubing in smaller diameter sections. Material is heated, and while hot, stretched and reduced in diameter to achieve desired wall.
Hot Working: The mechanical working of metal above the re-crystallization temperature.
HR-P&O: Hot rolled pickled and oiled sheet.
HSR: Hot, Stretch Reduced Pipe.
Hydraulic Cylinder Tubing: This tubing is, as the name implies, used to produce hydraulic
cylinders. It is available in two grades, regular DOM and Special Smooth ID (SSID). DOM is not
furnished with an ID of cylinder quality. The ID is sometimes surface finished by the steel
service center. SSID tubing is an excellent choice for certain types of hydraulic cylinders where
no further finishing of the ID is desired or required.
Hydraulic Fluid Line Tubing: Probably the highest quality carbon or alloy tubing made. Its
name tells you the applications for which it is used. Special conditions are required of the tubing;
special surface finishing, flare-ability, certain Rockwell hardness, restrictive elongation, and in
many cases, special pressure testing procedures.
Hydronic Heating System: A system containing a boiler to heat water; a system of pipe,
fittings and valves to control water flow; and heat releasing devices such as radiators or underfloor
Hydrostatic Test: A mill test that is normally required by specifications. The ends of the pipe
are sealed and high-pressure water is applied into the pipe at predetermined pressure for
specific period of time as required by the various specifications.
ID: Inside Diameter.
Impact Extrusion: A cold forming process in which the metal is forced by impact to flow
around the punch, forming a tube with a solid bottom.
Impact Test: A test to determine the energy absorbed in fracturing a test bar at high velocity. The test may be in tension or in bending, or it may properly be a notch test if a notch is present,
creating multi-axial tresses. See Mechanical or Destructive Testing.
Inclusions: Particles of non-metallic impurities, usually oxides, sulfides, silicates that are
mechanically held in steel during and after solidification.
Indirect Extrusion (inverted): An extrusion process in which the metal is forced back inside a
hollow ram that pushes the die.
Induction Hardening: A process of hardening a ferrous alloy by heating by means of electrical
induction above the transformation range and then cooling as required.
Induction Heating: A process of heating by electrical induction.
Industrial Piping: Piping systems used in manufacturing plants, factories, processing plants,
laboratories and other commercial applications.
Ingot: Solid form of steel; usually suitable for re-smelting and re-working.
Initial Creep: The early part of the time-elongation curve for creep, in which extrusion
increases at a rapid rate.
Ink Mark: Continuous printing identification.
Inlet: A branch opening that allows a flow to join the run.
Inside Diameter (ID): The distance of a straight line passing through the center of a pipe from
one inside pipe wall to the opposite inside wall.
Inside Hex Head Bushing: A bushing on which the hex head is smaller than the male pipe
Integral Finned Tubing: Tubing with raised surface fins formed from the wall of the tube itself.
Intergranular Corrosion: See Carbide Precipitation.
Internal Soundness: Refers to condition of material lack of defects, pipe, segregation, nonuniformity
IPS: Iron Pipe Size.
Iron: A metallic element. In the steel industry, iron represents the product of a blast furnace
containing 92% to 94% iron. Blast furnace iron is also called pig iron or hot metal.
Iron Oxide: A combination of iron and oxygen molecules known as “rust”.
Iron Pipe Size (IPS): Term referring to the standard measurement for pipe originally set by the
American National Standards Institute (ANSI); same as Nominal Pipe Size (NPS).
Isothermal Anneal: See Heat Treatment.
JIC Joint Industry Conference: As a prefix, generally indicates tubing for hydraulic
applications. (now obsolete).
Joint: The point in a piping system at which a connection is made; joints connect pipe, fittings
and valves to form a system. Also a single length of pipe can be called a joint.
Jominy Test: Hardenability test performed usually on alloy steels to determine depth and
degree of hardness resulting from a standard end quenching method using cold water.
Killed Steel: Steel deoxidized with a strong deoxidizing agent, such as silicon or aluminum; in
order to reduce the oxygen content to a minimum so that no reaction occurs between carbon
and oxygen during solidification.
Kip: Unit of weight equal to 1,000 pounds dead weight.
KSI: K equals I,000, thus the term is actually K (1,000) psi. The P has been dropped, and KSI
is the new term. (i.e. 50 KSI = 50,000 psi).
L: Low-Carbon stainless steel.
Ladle: A large vessel into which molten steel or molten slag is received and manipulated.
Ladle Analysis: Chemical analysis obtained from a sample taken during the pouring of the
Laminations: Defects resulting from the presence of blisters, seams or non-metallic inclusions
aligned parallel to the worked surface of a metal.
Lap: A surface defect appearing as a seam caused from folding over, during hot rolling, fins or
sharp corners and then rolling or forging, but not welding, them into the surface.
Lap Joint Flange: A free floating flange that is bolted over a stub end fitting that has been
welded to steel pipe. A lap joint flange can be used to join a pipeline that may later be
Lap Weld (L.W.): A term applied to a weld formed by lapping two pieces of metal. The two
pieces of metal are pressed or hammered along the longitudinal joint produced. A welding
process for tubes or pipe in which the edges of the skelp are beveled or scarfed so that when
they are over-lapped, they can be welded together.
Large OD Pipe: Pipe of NPS 14 and larger.
Laundry Tray Pump: A sump pump installed under a sink to pump laundry water into the
Leaded Carbon Steels: Lead improves the machine-ability of steels that have not been resulphurized
or re-phosphorized. Nearly all carbon steels of the 1000 (as well as 1100) series are
now available with 0.15 to 0.35 percent lead. Since machine-ability and particularly finish
requirements are the only reasons for using leaded grades, the extra cost over the straight
carbon, non-leaded steels must be justified. This usually occurs when both machine-ability and
mechanical properties are important requirements.
Leaded Resulphurized Steels: Most of the re-sulphurized grades are available with the
addition of 0.15 to 0.35 percent lead. The lead addition, which is insoluble in the steel,
augments the effect of sulphur, reducing friction and permitting a further increase in machining
speed, and better finish. With screw machine parts where more than 50 percent of the starting
stock become chips, there may be justification for the higher cost, especially when meeting high
finish requirements. Since leaded steels cost more than similar nonleaded compositions, the
increased cost is wasteful where machine tools are already being operated at maximum speed
on plain re-sulphurized steel. On the other hand, full advantage can be taken on machine tools
that have been designed for higher speeds. Leaded re-sulphurized steels are often used when
problems arise during long runs of screw machine parts. For example, surface finish was the
deciding factor in selecting leaded steel for parts of about 1/2 inch and 3 inches long made from
1141 steel. The finish requirements on the ends of the parts could not be met in the cut-off
operation when 1141 was used, and a secondary facing operation was necessary. A change to
leaded 1141 steel provided just enough improvement in the cut-off operation to meet the finish
requirements. Elimination of the additional facing operation slightly more than offset the
additional cost of the leaded grade.
LGTH: Length or joint of pipe.
Lifts: A term used to describe the bundles of small inch pipe as shipped.
Line Pipe: Steel Pipe used to carry gas and oil horizontally.
Long Nipple: A nipple with an unthreaded surface of 2 inches or more between the external
threads on each end.
Low-Carbon Stainless Steel: Stainless Steel with less than 0.03% carbon; often identified as
L for low carbon.
Low Heel Inlet: An inlet on the back and near the bottom of an ell fitting.
LR: Long radius is a term used in describing the center-to-center dimension of a butt weld
elbow. The radius is 1-½ times the pipe size.
LTC: Long Threads and coupling.
LW: Lap Weld, an obsolete method for producing pipe 5 inches in diameter and over.
Machine-ability: A measure of the relative ease with which steel may be machined.
Machining: In general, the cutting away of the surface of a metal by means of power driven
machinery. Specifically, a method of conditioning steel by machining away the surface.
Macroetch: A testing procedure for revealing porosity, inclusions, gross non-metallics,
segregation, etc. Surface of the test piece should be reasonably smooth or even polished. After
applying a suitable etching solution, the structure developed by the action of the reagent may be
Macroscopic Stresses: Residual stresses of such scope that relatively large areas of the
material or the whole specimen are involved. These stresses are accompanied by strain
measurable with ordinary extensometers under appropriate test conditions.
Macrostructure: The structure and internal condition of metals are revealed on a ground or
polished (and usually etched) sample, by either the naked eye or under low magnification (up to
about IO diameters).
Magnaflux: An inspection given to highly stressed parts of steel by suitably magnetizing the
material and applying a prepared magnetic powder that adheres along lines of flux leakage; the
existence of surface and subsurface discontinuities can be shown.
Male Pipe Threads (MPT): Threads that occur on the outside surface of a pipe or a fitting.
Malleability: The property that determines the ease of deforming a metal when the metal is
subjected to rolling or hammering. The more malleable metals can be hammered or rolled into
thin sheet more easily than others.
Mandrel: This term has two definitions.
- A rod used to retain the cavity in hollow metal products during working.
- A metal bar around which other metal may be cast, bent, formed or shaped.
Mandrel Drawn: Used to obtain closer ID, or OD or wall thickness tolerances. It creates
improved mechanical properties. (If a product is mandrel drawn, it is designated as DOM.)
Martensite: An unstable constituent in quenched steel, formed without diffusion and only
during cooling below a certain temperature. Martensite is found along the weldline of ERW Pipe
that is not heat-treated. The structure is characterized by its needle like appearance on the
surface of a polished and etched specimen. Martensite is the hardest of the transformation
products of austenite. In most steels, as-quenched martensite must be tempered normalized to
make it suitable for use.
Martensitic Stainless Steel: A type of straight chromium stainless steel.
McQuaid-Ehn Test: A special test for revealing the austenitic grain size of ferritic steels when
the steel is heated to 1700º F and carburized. There are eight standard McQuaid-Ehn grain
sizes; sizes 5 to 8 are considered fine grain and sizes under 5 are considered coarse grain.
Mechanical Joint (MJ): The joining of two ends of pipe or fitting without welding, threading, or
socketing. The mechanical joining can be by mechanical couplings of grooved pipe or via a
Mechanical Properties: Physical properties of the steel used to make pipe; examples of these
properties are tensile strength, elongation, hardness, etc.
Mechanical or Destructive Testing:
- Tension Test: This test is used to determine the strength (Tensile Strength) and
ductility (Yield Strength) of tubular products. It is an approved ASTM practice to make
tension tests on a full section of the tube or pipe when within the capacity of the testing
machine. When it is impracticable or impossible to test in full section, the test is made on
a strip machined from the tube or pipe. In the case of a tube or pipe having a wall
thickness of 3/4 inch or heavier, it is approved ASTM practice to use the standard ASTM
round two-inch gage length specimen.
- Flattening Test: This test is used to determine ductility, and is conducted by subjecting
rings cut from the tube or pipe to a prescribed degree of fattening between parallel
plates. The severity of the flattening tests is measured by the distance between the
parallel plates and is varied according to the dimensions, composition and condition of
the tube or pipe. The flattening test specimen should not be less than 21
/2 inches in
length and should be flattened cold to the extent required by the applicable specification.
- Reverse Flattening Test: This test is designed primarily for application to electric
welded tubing for the detection of flash overlaps and lack of weld penetration. The
specimen consists of a length of tubing approximately 4 inches long that is split
longitudinally at 90 degrees on each side of the weld. The sample is then opened and
flattened with the weld at the point of maximum bend.
- Crush Test: This test, sometimes referred to as an upsetting test, is usually made on
boiler and other pressure tubes for evaluating ductility. The specimen is a ring cut from
the tube, usually about 21
/2 inches long; for tubing 3
/4 inch OD and smaller the specimen
length is usually about 21
/2 times the OD. It is placed on end and crushed endwise by
hammering or pressing to the distance prescribed in the applicable specification.
- Flange Test: This test is made to determine the ductility of pressure tubes and their
ability to withstand the operation of beading into a tube sheet. The test is made on a ring
cut from a tube, usually not less than 4 inches long, and consists of having a flange
turned over at right angles to the body of the tube to the width required by the applicable
- Flaring Test: For certain types of pressure tubes this test is performed to indicate
ductility and suitability for flare type fittings. The test consists of expanding a sample
from the tube, or the end of the tube, with a tapered mandrel until the diameter has been
increased to extent required by the applicable specification.
- Bend Test: The test is bending two samples, at room temperature, to an inside
diameter, as designated by the applicable product specification, to the extent specified
without major cracking on the outside of the bent portion. The speed of bending is
ordinarily not an important factor.
- Impact Test: This is a test in which a selected specimen, machined or surface ground
and notched, is struck and broken by a single blow in a specially designed testing
machine, and the energy absorbed in breaking the specimen is measured.
- Hardness Test: The hardness test is a measure of resistance to penetration. In the
case of steel, the hardness test is a quick approximation of tensile strength. The most
commonly used methods to check hardness are the Rockwell and Brinnell tests. For
details of these tests, reference should be made to ASTM A 370.
- The following tests, not described in ASTM A 370, are made when required by
Reverse Bend Test:This test is designed primarily for application to electric welded
tubing for the detection of flash overlaps and lack of weld penetration, The specimen
consists of section 4 inches in length from annealed tubing in sizes larger than 1
nominal lD that is split longitudinally 90º, on each side of the weld. The sample is then
opened and bent around a mandrel having a diameter four times the wall thickness with
the mandrel parallel to the tube and on the outside of the tube. The weld is held at the
point of maximum deformation.
- Test Performed at Low Temperatures or Elevated Temperatures: Some tubular
products are subjected to tests performed at low temperatures or elevated temperatures
such as low temperature impact test and elevated temperature tensile test.
- Hydrostatic Testing: The Hydrostatic Test consists of filling the tube with water (hydro)
and applying hydrostatic pressure. This test is not intended to bear a direct relationship
to bursting pressures, working pressures or design data.
Mechanical Properties: Those properties of a material that reveal the elastic and inelastic
reaction when force is applied, or that involve the relationship between stress and strain; for
example, the modulus of elasticity, tensile strength, yield strength, and fatigue limit. These
properties have often been designated as physical properties; but the term mechanical
properties is much preferred. See Physical Properties.
Mechanical Tubing: Used for a variety of mechanical and structural purposes as opposed to
pressure tubing that is used for the conduction of fluids under pressure. It is commonly
manufactured to consumer specifications covering chemical analysis, mechanical properties
and often to special dimensional tolerances. It is used for such a variety of purposes that it is
impractical to subdivide it into classifications as are used for other classes of tubing.
Medium Anneal: See Heat Treatment.
Metallurgy: The science that deals with the extraction of metals from their ores and the
adaptation and application of these metals to the uses for which they are intended.
Micro-cleanliness: Refers to the extent or quantity of non-metallic inclusions observed by
examination under a microscope.
Mid-Welds: Two or more joints welded to form one long joint.
Mil: Identifier for specifications of the United States Department of Defense.
Minimum Wall: Any wall having tolerances specified all on the plus side. Minimum thickness
permissible calculated by subtracting minus tolerance from nominal wall.
Modulus of Elasticity: The slope of the elastic portion of the stress-strain curve in mechanical
testing. The stress is divided by the unit elongation. The tensile or compressive elastic modulus
is called Young’s modulus; the torsional elastic modulus is known as the shear modulus, or
modulus of rigidity.
Modulus of Rigidity: In torsion test, the ratio of the unit shear stress to the displacement
caused by its per unit length in the elastic range. This modulus corresponds to the modulus of
elasticity in the tension test.
Molybdenum: An alloying element commonly used in low alloy and other steels to increase
harden-ability, commonly called “moly”.
MPT: Male Pipe Threads.
MSS: Abbreviation for the Manufacturer’s Standardization Society.
NASPD: National Association of Steel Pipe Distributors.
NBS: National Bureau of Standards.
NFPA: National Fluid Power Association.
Necking Down: The narrowing, or constricting to a small cross-sectional area which occurs at
a localized place on a tensile test piece while it is being pulled.
Net Ton (N.T.): 2,000 pounds.
Nipple: A short piece of pipe 24 inches or less in length, plain inside and threaded outside at
both ends, used to connect pipe, fittings, and valves.
Nitriding: A process of case hardening in which a ferrous alloy, usually of special composition,
is heated in an atmosphere of ammonia or in contact with nitrogenous material to produce
surface hardening by the absorption of nitrogen, without quenching.
NOM (Nominal): Name given to standard pipe designations 1/8 inch through 12 inch. Does not
indicate actual ID measurements. Wall thickness is also expressed as nominal.
Nominal Pipe Size (NPS): NPS is approximately equal to the inside diameter of pipe with an
actual inside diameter of less than 14″; in pipe sizes larger than 14″, NPS is equal to the outside
diameter. NPS is identical to Iron Pipe Size (IPS).
Non-Destructive Testing: 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.
Non-Ferrous Metal: Metal which does not contain iron.
Normalize: The normalizing process that is commonly applied to steel articles of heavy section
consists of heating to a temperature about the critical range (about 1,600ºF) and cooling in still
air. See Heat Treatment.
Normalizing: An annealing process that consists of transforming a ferrous article fully to
austenite and then cooling in air.
Notch Brittleness: Susceptibility of a material to brittleness in areas containing a groove,
scratch, sharp fillet or notch.
NT: Net Ton (2,000 lbs.)
OCTG: Oil Country Tubular Goods.
OD: Outside Diameter.
OH: Open Hearth method of steel making.
Oil Country Pipe (Oil Country Tubular Goods): Steel pipe used in the petroleum industry as
drilling pipe or tubing and casing pipe.
Oiled: Pipe that is usually pickled, and then is oiled; however, it may be oiled without being
Oiling: Application of suitable oil to final product to retard rusting. Where surface is a
consideration, it is also desirable in reducing friction scratches that may develop in transit. The
oil coating is not intended to serve as a lubricant for subsequent fabrication. See Coating for
types of Oiling.
Open Hearth Furnace: A method of turning iron into steel. There may be only a few open
hearth furnaces left, as they have become obsolete due to the introduction of the Basic Oxygen
Furnace that is faster and thus less costly.
Outlet: Branch opening that allows part of the flow to leave the run.
Outside Diameter: The distance of a straight line passing through the center of the pipe from
one outside rim of the pipe to its opposite outside rim.
Ovality: The difference between the maximum and minimum diameters of any one section of
round tube, by actual measurement.
Overbending: Allowance for springback when bending metal to a desired angle.
Oxidation: In its simplest terms, oxidation means the combination of any substance with
oxygen. Rust Scale developed during heat treatment is a form of oxidation.
Oxide: A compound consisting of oxygen and one or more metallic elements.
Oxygen Steel: Steel made with the use of an oxygen blast, as an alternate or adjunct with air,
to remove impurities in the melting process. Increases rapidity of the process.
P & O: Pickled and Oiled, a pipe coating method or process.
Pass: There are two common definitions that apply to the steel industry:
- Movement of a piece of steel through a stand of rolls.
- The open space between two grooved rolls through which is rolled the steel that is being
Passivating: Immersion of steel in an acid bath to remove surface impurities and to render the
Passive Film: A thin, transparent, protective chromium oxide film which forms on the surface of
stainless steel pipe and enables the stainless steel to resist corrosion.
P.E.: Abbreviation used for “plain ends”.
Peeler: A lathe like machine in which tube rounds have about two (2) percent of their surface
removed to reduce seams and other surface defects.
PERC: Plain End Roller Cut.
PELC: Plain End Lathe Cut.
Permanent Set: Plastic deformation.
PESC: Plain End Square Cut (or Saw Cut).
Physical Properties: Those properties familiarly discussed in physics, exclusive of those
described under mechanical properties; for example, density, electrical conductivity, coefficient
of thermal expansion. This term has often been used to describe mechanical properties, but this
usage is not recommended. See Mechanical Properties.
Pickle: See Pickling.
Pickled Tubing: Tubing has had the scale from hot fabrication or heat treatment removed by
one of several types of acid solutions.
Pickling: An operation by which the scale formed on the surface of the tube during piercing or
heat treatment is removed by the chemical action in sulfuric acid. After the acid bath, the tubing
is rinsed (passivated) in water.
Piercing: A seamless tube-making method in which a hot billet is gripped and rotated by rolls
or cones and directed over a piercer point that is held on the end of a mandrel bar.
Pig Iron: Blast furnace iron, Hot Metal used to produce steel.
Pipe: Pipe is a closed metal cylinder used to transport gases and liquids from one point to
another as well as having structural uses.
Pipe Dope: A compound of plastic type materials, sometimes called Tread Compound or
Thread Lubricant, used to lubricate pipe threads and improve the seal.
Pipe Schedule: A listing of the American National Standards Institute (ANSI) to indicate the
wall thickness of pipe.
Pipe Size Tubing: This type of tubing can be a competitive product versus pipe in price and
physical properties. It is not pressure tested, but can be used in a variety of non-code, nonspecification
Piping: An assembly of pipe and/or tubing used in a system.
Pit: A sharp depression in the surface of metal.
Pitch: The number of threads per inch of thread surface on a pipe.
P.I.W.: Pounds per inch of width.
Plain End: Pipe with the ends left as they are cut, without special treatment.
Plastic Deformation: Permanent distortion of a material under the action of applied stress.
Plug: A pipe fitting with a male thread that is used to close the opening in a pipe or another
fitting; also, a rod or mandrel that fills a tube as it is drawn through a die.
Polishing: The act of removing a specific amount of stock to produce a desired finish.
Precipitation Hardness: See Age Hardening.
Pressure Pipe: Pipe designed to withstand a specified internal pressure; used in supply piping
systems, also called Supply Pipe.
Pressure Tank: A container used to store both the fluid and the pressure needed to move the
fluid through the supply system.
Pressure Tubing: Pressure tubing is small inch seamless pipe utilized for conveying critical
fluids or gases under pressure. It can be subjected to elevated temperatures or cryogenic
temperatures, and often exposed to corrosive media. Applications of pressure tubing are
frequently governed by regulatory codes that influence design by stipulating approved steels,
method of manufacture, strength criteria, code, joint efficiency, etc. Pressure tubing is suitable
for bending and further fabrication. Subdivisions of pressure tubes are boiler and super-heater
tubes, standard tubes, oil still tubes, heat exchanger and condenser tubes. Pressure tubes are
produced to actual outside diameter and minimum or average wall thickness (as specified by
the purchaser) and may be hot finished or cold finished, as specified. Wall thickness is
commonly specified in decimal parts of an inch rather than by gage numbers. Gage numbers for
tubular products refer to the Birmingham Wire Gage. In order to specifically indicate what wall
thickness is required, it is recommended that the gage system be identified and the nominal
thickness required be shown, for example, 16 BWG (0.064 inch). Usually used to describe 1½”
and smaller seamless pipe.
Process Annealing: A process by which a ferrous alloy is heated to a temperature close to,
but below, the lower limit of the transformation range and is subsequently cooled. This process
is applied in order to soften the metal for cold working.
Process Temper: A tempering operation performed to improve subsequent fabrication of the
material (machining, cold working etc.). See item A under Tempering.
Profilometer: An instrument used for measuring surface finish. The vertical movements of a
stylus as it traverses the surface are amplified electromagnetically and recorded (or indicated)
as the surface roughness.
Proportional Limit: The greatest stress a material is capable of sustaining without a deviation
from the law of proportionality of stress and strain. If the load is removed for any stress up to
this point, the material will spring back, or assume its original dimensions.
Protector: Sleeve over pipe ends to protect the bevel or the threads.
PSI: Pounds per Square Inch.
PSIG: Pounds per Square Inch Gage.
P-Trap: A fitting shaped like the letter P in which liquid remains to prevent the flow of gases
back into a piping system.
Pump: A device that raises, transfers or compresses fluids or gases by suction or pressure.
Pyrometer: An instrument used for measuring a product’s surface temperature.
Quality: The term “quality” refers to the suitability of the steel to meet specified requirements
for which it is intended.
- Commercial Quality Sheet and Bands (CQ): Commercial quality sheet and bands are
usually produced from rimmed, capped or semi-killed steel. Because of the segregation
occurring in the solidification of these types of steels, CQ materials are less ductile than
either Drawing Quality or Drawing Quality Special Killed material and can be expected to
show wider variations in mechanical properties and chemical composition. In addition,
some CQ sheet may be subject to some loss of ductility over time; bands, however, are
subject to strain aging as they receive no processing. If sheet must be essentially free
from stretcher strains during fabrication, it should be roller leveled just before the forming
- Drawing Quality Sheet and Bands (DQ): Drawing quality sheet and bands are more
ductile and more uniform in chemical composition than CQ material. Some DQ sheet
may be subject to some loss of ductility with time. DQ material is produced from
specially selected steel and carefully processed to result in more-uniform drawing
properties than CQ material. Hot rolled DQ sheet and bands are used to make parts that
are too difficult for the forming properties of hot rolled CQ sheet and bands. Drawing
quality sheet and bands are subject to coil breaks, stretcher strains and fluting in the asrolled
condition. If DQ sheet is to remain essentially free of stretcher strains through
fabrication, it should be roller leveled by the customer before forming.
- Drawing Quality Special Killed Sheet and Bands (DQSK): Drawing quality special
killed sheet and bands are rolled from aluminum-killed steel produced by special
steelmaking and processing practices. DQSK sheet and bands have forming
characteristics superior to CQ and DQ sheet and bands. These characteristics make it
excellent for use in severe drawing operations. It is recommended for processes in
which delays between draws would detrimentally affect the drawing performance of CQ
and DQ materials. There is no loss of ductility with time.
- Structural (Physical) Quality Sheet (STRL QUAL): Structural (Physical) quality sheet
and bands are ordered when specific mechanical properties are required. Usually,
orders specify hardness (Rockwell B) or tensile properties. In specifying mechanical
properties, the customer should carefully consider the compatibility of the properties with
- Special Soundness Quality: Special soundness quality is produced by employing
special steelmaking practices (including controlled phosphorus and sulphur) and
finishing practices. With these practices, a high degree of internal soundness,
homogeneity, and uniformity of chemical composition and grain control.
Quench: Quenching is a treatment consisting of uniformly heating, to a temperature above the
critical range and cooling rapidly in a liquid medium.
Quench Hardening: A process of hardening a ferrous alloy of suitable composition by heating
within or above the transformation range and cooling at a rate sufficient to substantially increase
the hardness. The process usually involves the formation of martensite.
Quenching: A process of rapid cooling from an elevated temperature by contact with liquids,
gases or solids. See Heat Treatment.
Quenching Crack: A fracture resulting from thermal stresses induced during rapid cooling or
Quenching and Tempering: Consists of heating the steel to the proper temperature, holding
at that temperature for a sufficient time to effect the desired change in structure, and quenching
in a suitable medium (water, oil, or air) depending upon the chemical composition and cross
section. After quenching, the steel is reheated to a predetermined temperature below the critical
range and then cooled under suitable conditions. It is sometimes necessary to use processes
that involve two or more combination heating and cooling operations such as quenching and
tempering, normalizing and tempering, or normalizing, quenching and tempering.
R & D: Reamed and Drifted, normally used in water wells where a guaranteed internal
clearance is necessary. All internal burns are removed smoothing the internal surfaces.
Radius: The distance of a straight line from the center of a circle to its edge.
Random Length: Steel pipe shipped in non-uniform (different) lengths.
Range: Allowable Lengths e.g. Range 1 = 20 foot Random Lengths; Range 2 = 30 foot random
lengths; Range 3 = 40 foot random lengths. These are not cut lengths, but are categorized
within a plus/minus tolerance.
Reamed: Having the internal burr removed from pipe ends by a slight counter-sinking.
Reamed and Drifted Water Well Pipe: Welded or seamless steel pipe with threaded and
recessed couplings; it is reamed on the ends and a plug is pulled through the pipe to ensure
Recessed: Counter-bored for a short distance when applied to couplings.
Recessed Coupling: A longer coupling in which the threads do not come all the way to the
edge of the coupling.
Reducer (Reducing Coupling): A coupling, larger at one end than the other, used to join two
pipes of different diameters.
Reducing Cross: A cross tee fitting with one or more opening of different sizes.
Reducing Ell: An elbow with ends of different diameters used to join pipes of two different
Reducing Flange: A flange tapped or bored smaller than the other flange to be used in a
Reducing Tee: A tee in which any one of its ends is smaller than the others.
Reducing Y: A Y in which any one of its openings is smaller than the others.
Reduction Area: In a tensile test, the difference between the original cross-sectional area and
that of the smallest area at the point of rupture; usually stated as a percentage of the original
area; also called contraction of area.
Refining Temperature: A temperature, usually just higher than the transformation range,
employed in the heat treatment of steel to refine the structure, in particular, the grain size.
Re-nitrogenized Steels: The influence of nitrogen is similar to that of phosphorus in producing
brittle chips that are particularly beneficial in internal machining operations such as in drilling or
tapping. Machine-ability rating is a function of both elements with optimum results in the region
of 0.06 percent phosphorus and 0.01 percent nitrogen.
Re-phosphorized Steels: The series 1200 open hearth steels are both re-phosphorized and
re-sulphurized. The phosphorus, by increasing the strength and hardness of the steel, promotes
chip breaking in cutting operations. The amount of phosphorus is limited, however, because the
excessive hardness produced by large quantities would actually be deleterious to machining
Resilience: The tendency of a material to return to its original shape after the removal of a
stress that has produced elastic strain.
Resistance Welding: A type of welding process in which the work pieces are heated by the
passage of an electric current through the contact. Such processes include spot welding, seam
or line welding and percussion welding.
Resulfurized Steels: The sulphur that is added for the purpose of increasing machine-ability
combines with the manganese in steel and precipitates as manganese sulfide inclusions. Depending on their size and orientation, the inclusions favor machining by causing the formation
of a broken chip instead of a stringy one, and by providing a built-in lubricant that prevents the
chip from sticking to the tool and undermining the cutting edge. The chip that forms breaks more
readily and is particularly helpful in milling, tapping, slotting and reaming, since the chip is forced
to move within a confined area in each of these operations. Resulfurized grades generally cost
more than plain carbon steels, and it is, therefore, advantageous to purchase resulfurized
grades only where the higher steel cost can be offset by lower machining costs. Their use is
also of advantage when finish requirements are high because of savings on tooling costs that
can normally be expected.
Return Bend: An elbow fitting that joins two parallel pipes and changes the direction of the run
by 180 .
Reverse Bend Test: See Mechanical or Destructive Testing.
Reverse Flattening Test: See Mechanical or Destructive Testing.
Revent Pipe: Pipe that connects waste pipe to the vent stack in a DWV system.
Rimmed Steel: A low-carbon steel that meets the following parameters. Note: The term rimmed comes from the fact that during gradual cooling, freezing moves inwards from the
sides, the molten portion at the top of the ingot becomes smaller and smaller and is said to “rim
in” until finally the whole top is solidified.
- Is effervescent when cast and during a considerable part of its solidification;
- Neither rises nor falls in the mold to any marked extent;
- When completely solidified, has no piping, but has blowholes centrally located and deepseated
below the surface;
- Has been cleansed from some of the-impurities and dirt because of their rising to the top
during the agitation of the molten metal by the escaping gases; and
- Has a cross section divided into three fairly well-defined zones:
- A very clean thin outer layer of nearly the same chemical composition as when
- A central portion; and
- An intermediate portion. The three zones are positively and negatively segregated
with respect to metalloids.
- A very clean thin outer layer of nearly the same chemical composition as when
Riser: A vertical pipe in a water system that extends one story or more; principal vertical supply
R/L: Random Lengths, various lengths of pipe but each within a specific allowable range.
Rockwell Hardness: See Hardness.
Roto-Rock (Tube Reducing or Rockrite): A method of cold finishing tubing in which a
machine rolls or rocks a split die over a tube. The tube is supported on the inside by a tapered
Roll Forming: (As applied to tube manufacture) A process of forming flat-rolled material into
Roller Straightening: A process involving a series of staggered rolls, between which rod,
tubing and shapes are passed for the purpose of straightening. The process consists of a series
of bending operations.
RMS: Root Mean Square, a measure of surface finish on metal.
Run: That portion of a fitting that goes in a straight line in the direction of the flow of the pieces
of pipe to which it is connected.
SAE: Society of Automotive Engineers.
Sanitary System: See Drain Waste and Vent (DWV) System.
SAW: Submerged Arc Weld.
SC: Square Cut Ends.
Scale: Oxide of iron that forms on the surface of pipe.
Scale Free: The absence of loose scale on a hot finished tube, typically achieved through
pickling or blasting.
Scarfing: Cutting surface areas of metal objects. This operation cuts surface defects from
ingots, billets, pipe, or the edges of plate that are to be beveled for butt welding. Also used to
describe the removal of the weld bead from the ERW pipe manufacturing method.
Schedule Numbers: ANSI numbers assigned to pipe depending upon wall thickness.
Screwed Fittings: Pipe fittings with threaded ends; also called threaded fittings.
Seamless Steel Pipe: Pipe which is manufactured by heating a solid cylindrical piece of steel,
rotating it, while punching or drilling its center, sizing rolls are then used to achieve the desired
size. There is no seam or weld.
Seat: Contact sealing surface in a union.
Segregation: The result of the natural phenomenon in the solidification of a steel ingot in which
various components of the steel, having the lowest freezing point, are concentrated in parts of
the ingot last to solidify.
Semi-Killed Steel: Steel that is characterized by variable degrees of uniformity in composition,
that are intermediate between those of killed and rimmed steel. They are deoxidized less than
killed steels. Most carbon plates are made from semi-killed steels except where higher quality is
specified or required.
Sensitization: See carbide precipitation.
Sensitized Pipe: Pipe in which carbide precipitation or intergranular corrosion has occurred.
Series: The number assigned to an alloy group of stainless steel by AISI. For example, Series
300 is chromium-nickel stainless steel.
Service Ell: See Street Ell.
Service Tee: See Street Tee.
Sheet: A rolled steel product rectangular in cross section and form of thickness 0.006 through
0.229 inch with sheared, slit or sawed edges.
Shell: In tubing terminology, shell generally indicates a hollow, like in tube hollow.
Shielded-Arc Welding: Electric arc welding in which the metal is protected from the
atmosphere. An inert gaseous atmosphere or flux-coated electrodes may be used.
Short Nipple: See Shoulder Nipple.
Shoulder Nipple: A nipple somewhat longer than a close nipple, with an unthreaded surface
between the external threads on each end; also called a Short Nipple.
Sink Drawing: Sink drawn tubing is produced by drawing the welded tube through a die with
only the OD being controlled. This operation is performed when closer tolerances or a better
surface might be required on the OD only and for enhanced mechanical properties. Sink drawn
tubing can be produced from either hot rolled or cold rolled steel, and ID flash can be any of the
conditions described above.
Sizing Methods: HF Hot Finished, CW Cold Worked, RT Rough Turned, G Ground.
Skelp: Hot rolled strip steel product basically used in the production of Welded Pipe. Is
sometimes used in the production of Heavy Wall Tubing.
Skiving: A process by which material is removed from the tube ID with a head containing
several cutting tools.
Slab: A semi-finished steel block having an oblong cross-section in which the width is at least
twice thickness. It differs from a bloom which has a square or nearly square cross-section.
Slip-On Flange: Type of flange that slips over steel pipe and is held in place by one or two
Slitting: The longitudinal splitting of the overall width of a flat product through rotary knives
mounted on a rotating arbor to reduce the original width or to cut two or more separate strips or
SMLE: Seamless, pipe without a seam or weld in its circumference.
Soak: To hold an ingot, slab, bloom, billet or other piece of steel in a hot chamber or pit to
secure uniform temperature throughout. Freshly stripped ingots are hottest in the interior,
whereas a cold object that is being heated is hottest at the surface. The term is used in
connection with heating of steel whether for forging or rolling or for heat treatment.
Soaking Pit: A furnace or pit for the heating of ingots of steel to make their temperature
uniform prior to rolling or forging.
Socket Weld: A method of welding in which the pipe is inserted into a recessed socket of the
fitting or flange and welded.
Socket Weld Fitting: A fitting with a recessed end or socket into which the pipe fits.
Socket Weld Flange: Type of flange which has a recessed socket into which the pipe fits.
Soft Anneal: See Heat Treatment.
Soil Line: That part of a DWV system inside a building that carries sewage from the toilets to
the building drain, made from Cast Iron.
Soldering: Joining metals by fusion of alloys that have relatively low melting points, most
commonly, lead-base or tin-base alloys that are soft solders. Hard solders are alloys that have
silver, copper, or nickel bases, and use of these alloys with melting points higher than 800ºF is
generally termed brazing.
Solution Anneal: See Heat Treatment.
Special Quality (Hot Rolled Bars): This quality requires freedom from visible pipe and
excessive chemical segregation. The product is rolled from billets that have been inspected and
conditioned as necessary to minimize surface imperfections.
Special Smooth I.D. (S.S.I.D.): A cold drawn tube in which special attention is paid to the
internal surface. Depth of pits and scores in ID are guaranteed to be below published maximum
depths. Microinch finish is guaranteed in ERW tubes.
Special Internal Soundness Quality: This quality is produced by employing special
steelmaking practices (including controlled phosphorus and sulphur) and finishing practices. With these practices a high degree of internal soundness, homogenity, uniformity of chemical
composition, and grain control is obtained. This quality is generally produced as a killed steel.
Specification (SPEC): A document defining the measurements, tests, and other requirements
to which a product must conform typically covering chemistry, mechanical properties,
tolerances, finish, reports, marking and packaging.
Spectrograph: An optical instrument for determining the presence or concentration of metallic
constituents in a material by indicating the presence and intensity of specific wave lengths of
radiation when the material is thermally or electrically excited.
Spheroidize Annealing: Any process of heating and cooling that produces a rounded or
globular form of carbide in steel.
Spinning: A type of forming (hot or cold) that involves rotating a tube at high speed against
fixed or rolling tools for the purpose of altering shape, size, etc.
Spiral Eccentricity: To some degree, spiraling eccentricity occurs in all seamless steel tubing
as a natural consequence of the rotary piercing process. The effect may be compared to gun
barrel rifling. The eccentric spiral makes a complete revolution in approximately every 30″ of
SR Short Radius: A term used to describe the center-to-center dimensions of a butt weld
fitting; the radius is 1 times the NPS Pipe Size.
SRL: Single Random Lengths, 16 to 22 feet in length.
S.S.C.I.: Steel Service Center Institute.
Stabilized Stainless Steel: Stainless steel to which a special alloy has been added to attract
carbon atoms and prevent carbide precipitation.
Stack: General term used to describe any vertical line in a DWV system.
Stack Vent: See Vent Stack.
S. T. & C.: Short Thread and Coupled.
Stainless Steel: Stainless Steel is a steel that meets the following definitions:
- A trade name given to alloy steel that is corrosion and heat resistant. The chief alloying
elements are chromium, nickel, molybdenum and silicon in various combinations with a
possible small percentage of titanium, vanadium, etc.
- By AISI definition, a steel product in non tubular form is called “Stainless” when it
contains 10.5 percent or more chromium.
Stainless Steel Pipe: Pipe made from iron-based alloys containing at least 11.5% Chromium.
Standard Pipe: One of the general classifications of steel pipe used in plumbing, ac/heating
systems, and structural applications.
Standard Weight (Std. or S.): (Is the weight/wall of steel pipe so designated over time as the
most common with the most common usages.) For sizes NPS 1
/8 through NPS 10 Standard
weight/wall is the same as Schedule 40.
Steel: Steel is an iron-base alloy, malleable in a temperature range as initially cast, containing
manganese, carbon, and often other alloying elements. For carbon steel and low-alloy steel, the
maximum carbon is about 2.0%; in high alloy steel, about 2.5%. The dividing line between lowalloy
and high-alloy steels is generally regarded as being at about 5% of metallic alloying
elements. Steel is to be differentiated from two general classes of irons; cast irons, on the highcarbon
side, and relatively pure irons such as ingot iron, carbonyl iron, and electrolytic iron, on
the low-carbon side. In some steels with extremely low carbon, the manganese content is the
principal differentiating factor. Steel usually contains at least 0.25% of manganese; ingot iron
contains considerably less.
Stencil: Spray painting the required markings on the pipe with such items as specification,
size, wall thickness, length, test pressure, grade, manufacturer, country of origin; certain
specifications may require additional markings.
STI: Steel Tube Institute (Formerly the Welded Tube Institute).
Straight Chromium Group: A group of stainless steels that contains chromium as its major
Straight Cross: A tee that has four openings of the same size set at right angles.
Strand: Product of Continuous Cast Process.
Strand Casting: Strand casting is the direct casting of steel from the ladle into slabs. When
two or more heats are cast without interruption, the process is called continuous strand casting. In strand casting, a heat of steel is tapped into a ladle in the conventional manner. The liquid
steel is then teemed into a tundish that acts as a reservoir to provide for a constant casting rate. The steel flows from the tundish into the casting machine and rapid solidification begins in the
open ended molds. The partially solidified slab is continuously extracted from the mold. Solidification is completed by cooling the moving steel surface. More than one strand may be
cast simultaneously, depending upon the heat and slab size. A reduction in size may be carried
out by hot working the product as it exits from the strand prior to cutting the cast section to
length. Chemical segregation is minimized due to the rapid solidification rate of strand cast
product. Steel produced from a strand casting operation is always fully killed steel, thus is
generally considered to have excellent surface quality.
Streamline Tubing: Extruded or drawn tubing of which the cross section is shaped like a
Street Ell: An elbow fitting in which one end is male and the other is female. Also called a
Service Ell or a Fitting Ell.
Street Tee: A tee fitting in which the openings to connect the run have one male end and one
female end and the third end is female; also called a Service Tee.
Stress: The load per unit of area. Ordinarily stress-strain curves do not show the true stress
(load divided by area at that moment), but a fictitious value obtained by always using the original
Stress Free: This term is used to designate tubing that has been hot rotary straightened. Since
no cold working stresses are developed in hot rotary straightening, the stress relief temper is not
necessary. Cold rotary straightening and stress relieving can be substituted for hot rotary
Stress Relief Anneal: See Heat Treatment.
Stress Relieving: A process of reducing residual stresses in a metal object by heating the
object to a suitable temperature and holding for a sufficient time. This treatment may be applied
to relieve stresses induced by casting, quenching, normalizing, machining, cold working or
Stretch Reduction: A technique employed in the manufacture of pipe to achieve its final size. It involves one or several Master sizes that are heated and then stretch-reduced or rolled under
tension through a number of stands to achieve a variety of pipe diameters and specific wall
Stretcher Leveling: Leveling where a piece of metal is gripped at each end and subjected to a
stress higher than its yield strength to remove warp and distortion. Sometimes called patent
Stretcher Straightening: A process for straightening rod, tubing and shapes by the application
of tension at the ends of the stock. The products are elongated a definite amount to remove
Stretcher Strains: Elongated markings that appear on the surface of some materials when
deformed just past the yield point. These markings lie approximately parallel to the direction of
maximum shear stress and are the result of localized yielding; same as Luders lines.
Strip: A flat-rolled steel product usually up to 12′ wide which can serve as the raw material for
Structural Quality (SQ or PQ): Structural (Physical) Quality sheet and bands are ordered
when specific mechanical properties are required. Usually, orders specify hardness (Rockwell
“S”) or tensile properties. In specifying mechanical properties, the customer should carefully
consider the compatibility of the properties with forming requirements.
Structural Tubing: Tubing used primarily for structural applications and produced in squares,
rectangles, rounds and shapes.
Submerged Arc Weld (SAW): A method of producing very large OD tubular products by
submersing the weld area in a flux.
Sump: Drainage pit used to store unwanted water.
Sump Pump: Device used to remove unwanted water (by suction, pressure or both) be located
in the drainage pit, the sump, itself.
Sunk Drawn: Tubing drawn through a die with no inside mandrel to control ID or wall
Supply Pipe: See Pressure Pipe.
Surface Inspection: The inspection of the surface of products for defects such as ingot cracks,
scabs, seams, burned steel, laps, twist, guide marks, etc.
Swaged: A mechanical reduction of the cross sectional area of a metal, performed hot or cold
by forging, pressing or hammering.
Swager: A machine used to reduce diameter or taper tubing. A pair of dies with grooves
corresponding to the desired diameter or taper hammer of the tube. These dies are actuated by
a number of horizontal rolls in a revolving cage and the impact causes the dies to revolve and
thereby work the tube diameter to the desired size or contour. Since it is extremely difficult to
make abrupt tapers, the taper on each side should be limited to about 4-1/2 degrees. The ID
finish of a tube is affected by the finish of the mandrel and the cleanliness of the tube. Shown
below are typical examples of swaged parts:
- Double Reduction
- Straight and Taper with Straight
- Bullet Taper
- Bullet Nose
Swaging: Swaging is a method of cold working tubing in which the reduction is accomplished
by hammering tubing to the desired dimension. The hammer blows are delivered rapidly against
the outside surface of the tube. An inside mandrel may or may not be used.
Taper: A gradual change in the outside diameter of threads on pipe where the diameter at the
ends of the pipe is the least.
Taper-tapped Coupling: A threaded fitting on which the threads at the end are rolled deep and
gradually become more shallow; used with threaded standard steel pipe for 2-½” and larger. A
coupling that has been tapered.
Tapped: Having female pipe threads.
Tapping: The act of pouring molten metal from a furnace into a ladle.
T & C: Threaded and coupled.
TBE: Threaded, Both Ends.
Tee: A fitting that has one side opening set at a 90 angle to the run.
Teeming: Act of pouring molten metal from a ladle into an ingot mold.
Temper: A condition produced in a metal or alloy by mechanical or thermal treatment and
having characteristic structure and mechanical properties. A given alloy may be in the fully
softened or annealed temper, or it may be cold worked to the hard temper, or further to spring
temper. Intermediate tempers produced by cold working (rolling or drawing) are called quarterhard,
half-hard and three-quarters hard, and are determined by the amount of cold reduction
and the resulting tensile properties. In addition to the annealed temper conditions produced by
thermal treatment are the solution heat treated temper and the heat treated and artificially aged
temper. Other tempers involve a combination of mechanical and thermal treatments and include
that temper produced by cold working after heat treating, and that produced by artificial aging of
alloys that are as-cast, as-extruded, as-forged and heat treated, and worked. Temper is a term closely associated with flat rolled sheet products; particularly cold rolled strip
and sheet. It is generally measured by Rockwell hardness, and is often the key to successful
fabrication and proper end use application. A customer may specify any of various hardness levels or tensile properties. A tube producer
needs to know the required temper. It is suggested that desired physical properties be
discovered/specified in order that the proper heat treatment be applied.
Tempering: A process of reheating quench-hardened or normalized steel to a temperature
below the transformation range, and then cooling at any rate desired. See Heat Treatment.
Tempering Annealing: A process of re-heating quench-hardened or normalized steel to a
temperature below the transformation range and then cooling it at any rate desired.
Tensile Strength: The value obtained by dividing the maximum load observed during tensile
straining until breakage occurs by the specimen cross-sectional area before straining. Also
called ultimate strength.
Tensile Test: The three results usually reported are:
- Yield Point – T\the stress at which there is a marked increase in deformation without a
proportional increase in load.
- Tensile Strength – the maximum load observed during the test before breakage occurs.
- Elongation – the length of stretch before rupture.
Tolerance(s): Permissible variations or deviation from a dimension.
Torsion: Strain created in a material by a twisting action. Correspondingly, torsion is also the
stress within the material resisting the twisting.
Toughness: A measure of ability to absorb energy and deform plastically before fracturing.
Transverse Tension Test: A tension test for evaluating mechanical properties of a material in
a direction transverse to that of rolling.
Trepanning: A process that bores a hole through a solid cylindrical steel bar.
- Elongation – the amount that a specified gage length containing the fracture has
stretched during the test, expressed as a percentage.
Tension Test: See Mechanical Testing or Destructive Testing.
Tests Performed at Low Temperatures or Elevated Temperatures: See Mechanical
Testing or Destructive Testing.
Thermal Treatment: Any treatment listed under annealing or heat-treating.
Thread Compound: See Pipe Dope.
Threaded: Having continuous, regularly spaced grooves and ribs to form a spiral pattern
around a pipe end; pipe and fittings may be threaded.
Thread Lubricant: See Pipe Dope.
Threaded and Coupled End: A description of steel pipe with ends that are threaded and to
which a coupling has been attached.
Threaded Flange: Type of flange with female pipe threads which is screwed to steel threaded
TO: Threads Only.
TOE: Thread One End.
T-304: See Type 304 Stainless Steel.
T-316: See Type 316 Stainless Steel.
Trap: Afitting with a U shaped segment that continuously retains a liquid to form a seal that
prevents the back passage of air without affecting the flow of liquids in the system.
Tube: A cylindrical conductor with a wall too thin to receive a standard pipe thread that meets
national standards for United States Standard Tapered Pipe Thread.
Tube Hollow: As a generic term for any ERW, SMLS or CDBW tube ready for further
processing such as cold drawing.
Tube Reducer: A machine in which a pair of rolls is used for cold rolling tubing and rod. These
rolls have a tapered groove around part of their surface, corresponding to the intended change
in outside dimension of the tube or rod. The stock is rotated between working strokes. This
process is somewhat different from the Pilger process in which the stock moves in the same
direction, as rolling proceeds; the axes of the rolls move back and forth parallel to the stock and
the direction of rotation of the rolls changes between the forward working stroke and the
backward return stroke. A fixed mandrel is used in rolling tubing.
Tube Reducing: Tube reducing is a method of cold working tubular products in which a pair of
rolls having tapered grooves is rolled and reciprocated along the outside of the tube so that
reduction of diameter and wall thickness is accomplished against a fixed, tapered mandrel or
the inside of the tube. Roll reliefs at the initial and final diameters permit advance and rotation of
the tube with each cycle. (It is used primarily on stainless seamless tubing.) Generally tubing to
be tube reduced is annealed before processing because of the higher reduction involved
compared to cold drawing (steel grade is also a factor). As in the case with cold drawing, tubes
are pickled to remove scale and then lubricated before tube reducing.
Tube Round: A term used to describe a seamless product ready to be shipped. Also
sometimes used instead of tube hollow. This term is also used as a synonym for Billet.
Tubing: A hollow shaped product with a relatively uniform wall thickness, generally round,
square, or rectangular, and manufactured to specified requirements for dimensions, chemical
analysis, mechanical properties and other characteristics (such as surface) required for
applications in aircraft, sanitary, mechanical, pressure, ornamental or structural uses. It is
generally specified to two dimensions, i.e., OD (Outside Diameter) and wall, ID (inside
Diameter) and wall, or OD and ID It is not primarily designed for use with standard threaded
pipe couplings or for applications where standard or heavy wall pipe is normally used.
Tubular Plumbing Goods: Products used to link sinks, tubs and lavatories to drainage piping.
Turkshead: Consists of a frame, mounted on a draw bench, containing four rolls with their
axes at right angles and so positioned as to provide an opening corresponding to the section to
be formed: round tubes are pulled through the rolls without internal mandrel support. The
outside corners of sections processed by these means do not have constant radii.
Turning: A method for removing the surface from a work piece by bringing the cutting edge of
a tool against it while the piece or tool is rotated.
Type: A subclass of a Series or alloy group. For example, Type 304 stainless steel is a special
individual class of Series 300 stainless steel. Types are also called grades.
Types of Steel: Killed, Semi-Killed, Rimmed, and Capped.
Type 304: Stainless Steel: One type of austenitic stainless steel containing 18% chromium and
8% nickel; most widely used for pipe and fittings; also called T-304 or 18-8.
Type 316 Stainless Steel: One type of chromium nickel stainless steel that has an additional
element, molybdenum added to prevent pitting; the second most commonly used stainless steel
for pipe and fittings; also called T-316.
Ultimate Strength: The greatest load per square inch of original cross-sectional area carried
during a tension test to failure. The term ultimate strength is preferred to Tensile strength.
Ultrasonic Testing: The method of detecting defects in tubes or welds by passing high
frequency sound waves into a material then monitoring and evaluating the reflected signals.
Unified Numbering System (UNS): This system was conceived and initiated by the SAPSociety
of Automotive Engineers. It is used to supplement already existing designation systems
(i.e., AISI, ASTM, AMS, etc.) It is just an attempt to coordinate various systems into an overall
The Unified Numbering System for metals and alloys (UNS) provides a means of correlating
many nationally used metal and alloy numbering systems currently administered by societies,
trade associations, and those individual users and producers of metals and alloys. This system
avoids the confusion caused by the use of more than one identification number for the same
metal or alloy, and the opposite situation of having the same number assigned to two or more
different metals or alloys.
A UNS designation is not, in itself, a specification, since it establishes no requirements for form,
condition, property, or quality. It is a unified identifier of a metal or an alloy for which controlling
limits have been established in specifications published elsewhere. The UNS establishes 18
series of designations for metals and alloys, 17 of which are currently active. Each UNS
designation consists of a single-letter prefix followed by five digits. In most cases, the letter is
suggestive of the family of metals identified: For example, A for aluminum, P for precious
metals, S for stainless steels.
Prefixes used in UNS
- Axxxxx Aluminum and Aluminum Alloys
- Cxxxxx Copper and Copper Alloys
- Exxxxx Rare Earth and Similar Metals and Alloys
- Fxxxxx Cast Irons
- Gxxxxx AISI and SAE Carbon and Alloy Steels
- Hxxxxx AISI and SAE H-Steels
- Jxxxxx Cast Steels (Except Tool Steels)
- Kxxxxx Miscellaneous Steels and Ferrous Alloys
- Lxxxxx Low Melting Metals and Alloys
- Mxxxxx Miscellaneous Non-ferrous Metals and Alloys
- Nxxxxx Nickel and Nickel Alloys
- Pxxxxx Precious Metals and Alloys
- Rxxxxx Reactive and Refractory Metals and Alloys
- Sxxxxx Heat and Corrosion Resistant Steels (including Stainless), Valve Steels, and
- Txxxxx Tool Steels, Wrought and Cast
- Wxxxxx Welding Filler Metals
- Zxxxxx Zinc and Zinc Alloys
Uniform Length: Steel pipe shipped in the same lengths.
Union: A fitting with three parts, two threaded ends with a nut between them, used to join two
pieces of pipe such that they may be easily disconnected.
Upset: The product of any cold or hot forming of material in which the metal is thickened by
being forced back into itself. It is usually done at a red metal heat by hammering or press
forging. Upset tubes are those whose ends have their walls so thickened for a short distance,
usually to such an extent that the threading leaves as great a thickness of metal below roots of
threads as in the main body of tubes. Upset tubes are much used as stay tubes; they are
sometimes called stove tubes.
Vacuum Treatment: Processes designed to remove undesirable gases and/or to improve the
internal micro-cleanliness of the product through use of a vacuum facility.
Vacuum Melting: Melting in a vacuum to prevent contamination from air, as well as to remove
gases already dissolved in the metal; the solidification may also be carried out in a vacuum or at
Valve: A device used to start, stop or regulate flow by means of a moveable part that opens or
obstructs passage through the valve body.
Vent Stack: A vertical line of pipe, usually through the building roof, that provides circulation of
air and relief of pressure in a DWV system; also called a Stack Vent.
Vickers Hardness Test: See Hardness.
Vic: Victaulic Groove Note: Victaulic is the trademark of Victaulic Corporation of America.
Victaulic Joint: Pipe is grooved near ends to accommodate a Victaulic coupling.
Wall: The conducting structure of a pipe or tube.
Waste Line: The part of a DWV system that carries waste products from tubs, sinks and
lavatories to the building drain.
Water Well Casing: Steel pipe produced by the electric weld or seamless process; used to
encase a drilled well.
Water Well Pipe: Category of standard pipe used in a water well.
Weld Bead: The built-up portion of a weld, formed either from the filler metal or from the parent
Weld Decay: Sensitization of stainless steel that has been caused by the heat of welding.
Weld Pad: A slight thickening of the wall in the weld area that occurs during the continuous
Welded Pipe: Pipe which is made by rolling a flat piece of steel into a long cylinder and
welding the edges together, forming a seam where the pipe is welded.
Welding: A process used to join metals by the application of heat. Fusion welding, which
includes gas, arc and thermal welding, requires that the parent metals be melted. This
distinguishes fusion welding from brazing. In pressure or resistance welding, joining is
accomplished by the use of heat and pressure without melting. The parts that are being welded
are pressed together and heated simultaneously so that recrystallization occurs across the
Welding, Arc: The method of uniting metals by use of an electric arc to raise the metal
temperature to the fusion point.
Welding, Electric Resistance: The method of uniting metals by passage of an electric current
through the metal, whereby the resistance of the metal results in a temperature increase at the
abutting surfaces sufficient to effect union. Pressure is generally applied to insure intimate
contact of the surfaces to be welded.
Welding, Fusion: Joining of metals by heating the adjoining parts to the melting point. The
molten puddle formed becomes the joint. Arc, gas and thermal welding are examples of fusion
Welding, Induction: A form of electric resistance welding wherein the welding heat is
generated within the metal by resistance to the flow of an electric current induced in the metal
by means of a circumferential or tangent coil.
Welding, Inert Arc: Arc welding in an atmosphere of an inert gas that serves to protect the
molten puddle from contamination and oxidation by preventing air from coming in contact with
the metal while it is at elevated temperatures.
Welding, Plasma Arc: The plasma arc process concentrates a jet stream of gas on a
restricted weld area, providing more control and uniformity of the weld that was before possible. Used to produce welded stainless steel pipe and tubing in the heavier wall thicknesses.
Welding Stress: The stress resulting from localized heating and cooling of metal during
Welding Neck Flange: Type of Flange with an extension that is connected by a single butt
weld to a fitting or a pipe.
Work Hardness: Hardness developed in metal as a result of cold working. See Cold Working.
Wrought Iron: A commercial iron product that contains little carbon and a considerable amount
of included slag that, due to subsequent working, gives a fibrous structure to the iron.
WWP: Prefix designating Federal Government Specifications for standard pipe pertaining to
requirements of the Federal Supply Service and the General Services Administration.
XH: Extra Heavy or Extra Strong.
XXH: Double Extra Heavy or Double Extra Strong.
Y: A fitting that joins three sections of pipe sometimes called WYE.
Yield Point: In mild or medium-carbon steel, the stress at which a marked increase in
deformation occurs without increase in load. In other steels and in non-ferrous metals, this
phenomenon is not observed. See Yield Strength.
Yield Strength: The stress at which a material exhibits a specified limiting deviation from
proportionality of stress to strain. An offset of 0.2 percent is used for many metals such as steel,
aluminum base, and magnesium base alloys, while a 0.5 percent total elongation under load is
frequently used for copper alloys.
Zinc Coating: Is a type of galvanizing coating that protects the base metal against corrosive
factors by sacrificing itself for the preservation of the metal. The selection of such a coating
depends directly on what the tube will be subjected to, atmospheric corrosion, painting
appearance, durability, etc.