Piping General Definitions

Piping General Definitions

Learn more about Piping General Definitions are essential for piping stress analysis, piping design and piping fabrication (include welding process). Therefor, Little P.Eng. for Engineers Training shares the the following piping definitions below:

  • Absolute Viscosity. Absolute viscosity or the coefficient of absolute viscosity is a measure of the internal resistance. In the centimeter, gram, second (cgs) or metric system, the unit of absolute viscosity is the poise (abbreviated P), which is equal to 100 centipoise (cP). The English units used to measure or express viscosity are slugs per foot-second or pound force seconds per square foot. Sometimes, the English units are also expressed as pound mass per foot-second or poundal seconds per square foot.

  • Adhesive Joint. A joint made in plastic piping by the use of an adhesive substance which forms a continuous bond between the mating surfaces without dissolving either one of them. Refer to Part D of this handbook.

  • Air-Hardened Steel. A steel that hardens during cooling in air from a temperature above its transformation range.1

  • Alloy Steel. A steel which owes its distinctive properties to elements other than carbon. Steel is considered to be alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits:

Manganese 1.65 percent

Silicon 0.60 percent

Copper 0.60 percent

or a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels:

Aluminum Nickel

Boron Titanium

Chromium (up to 3.99 percent) Tungsten Cobalt Vanadium

Columbium Zirconium


or any other alloying element added to obtain a desired alloying effect.

Small quantities of certain elements are unavoidably present in alloy steels. In many applications, these are not considered to be important and are not specified or required. When not specified or required, they should not exceed the following amounts:

Copper 0.35 percent

Chromium 0.20 percent

Nickel 0.25 percent

Molybdenum 0.06 percent

  • Ambient Temperature. The temperature of the surrounding medium, usually used to refer to the temperature of the air in which a structure is situated or a device operates.

  • Anchor. A rigid restraint providing substantially full fixation, permitting neither translatory nor rotational displacement of the pipe.

  • Annealing. Heating a metal to a temperature above a critical temperature and holding above that range for a proper period of time, followed by cooling at a suitable rate to below that range for such purposes as reducing hardness, improving machinability, facilitating cold working, producing a desired microstructure, or obtaining desired mechanical, physical, or other properties. (A softening treatment is often carried out just below the critical range which is referred to as a subcritical annealing.)

  • Arc Cutting. A group of cutting processes in which the severing or removing of metals is effected by melting with the heat of an arc between an electrode and the base metal (includes carbon, metal, gas metal, gas tungsten, plasma, and air carbon arc cutting). See also Oxygen Cutting.

  • Arc Welding. A group of welding processes in which coalescence is produced by heating with an electric arc or arcs, with or without the application of pressure and with or without the use of filler metal.

  • Assembly. The joining together of two or more piping components by bolting, welding, caulking, brazing, soldering, cementing, or threading into their installed location as specified by the engineering design.

  • Automatic Welding. Welding with equipment which performs the entire welding operation without constant observation and adjustment of the controls by an opera- tor. The equipment may or may not perform the loading and unloading of the work.

  • Backing Ring. Backing in the form of a ring that can be used in the welding of piping to prevent weld spatter from entering a pipe and to ensure full penetration of the weld to the inside of the pipe wall.

  • Ball Joint. A component which permits universal rotational movement in a piping system.

  • Base Metal. The metal to be welded, brazed, soldered, or cut. It is also referred to as parent metal.

  • Bell-Welded Pipe. Furnace-welded pipe produced in individual lengths from cut- length skelp, having its longitudinal butt joint forge-welded by the mechanical pressure developed in drawing the furnace-heating skelp through a cone-shaped die (commonly known as a welding bell), which serves as a combined forming and welding die.

  • Bevel. A type of edge or end preparation.

  • Bevel Angle. The angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member.

  • Blank Flange. A flange that is not drilled but is otherwise complete.

  • Blind Flange. A flange used to close the end of a pipe. It produces a blind end which is also known as a dead end.

  • Bond. The junction of the weld metal and the base metal, or the junction of the base metal parts when weld metal is not present.

  • Branch Connection. The attachment of a branch pipe to the run of a main pipe with or without the use of fittings.

  • Braze Welding. A method of welding whereby a groove, fillet, plug, or slot weld is made using a nonferrous filler metal having a melting point below that of the base metals, but above 800°F. The filler metal is not distributed in the joint by capillary action. (Bronze welding, the term formerly used, is a misnomer.)

  • Brazing. A metal joining process in which coalescence is produced by use of a nonferrous filler metal having a melting point above 800°F but lower than that of the base metals joined. The filler metal is distributed between the closely fitted surfaces of the joint by capillary.

  • Butt Joint. A joint between two members lying approximately in the same plane.

  • Butt Weld. Weld along a seam that is butted edge to edge.

  • Bypass. A small passage around a large valve for warming up a line. An emergency connection around a reducing valve, trap, etc., to use in case it is out of commission.

  • Carbon Steel. A steel which owes its distinctive properties chiefly to the carbon (as distinguished from the other elements) which it contains. Steel is considered to be carbon steel when no minimum content is specified or required for aluminum, boron, chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, or zirconium or for any other element added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese, 1.65 percent; silicon, 0.60 percent; copper, 0.60 percent.

  • Cast Iron. A generic term for the family of high carbon-silicon-iron casting alloys including gray, white, malleable, and ductile iron.

  • Centrifugally Cast Pipe. Pipe formed from the solidification of molten metal in a rotating mold. Both metal and sand molds are used. After casting, if required the pipe is machined, to sound metal, on the internal and external diameters to the surface roughness and dimensional requirements of the applicable material specification.

  • Certificate of Compliance. A written statement that the materials, equipment, or services are in accordance with the specified requirements. It may have to be supported by documented evidence.

  • Certified Material Test Report (CMTR). A document attesting that the material is in accordance with specified requirements, including the actual results of all required chemical analyses, tests, and examinations.

  • Chamfering. The preparation of a contour, other than for a square groove weld, on the edge of a member for welding.

  • Cold Bending. The bending of pipe to a predetermined radius at any temperature below some specified phase change or transformation temperature but especially at or near room temperature. Frequently, pipe is bent to a radius of 5 times the nominal pipe diameter.

  • Cold Working. Deformation of a metal plastically. Although ordinarily done at room temperature, cold working may be done at the temperature and rate at which strain hardening occurs. Bending of steel piping at 1300°F (704°C) would be considered a cold-working operation.

  • Companion Flange. A pipe flange suited to connect with another flange or with a flanged valve or fitting. A loose flange which is attached to a pipe by threading, van stoning, welding, or similar method as distinguished from a flange which is cast integrally with a fitting or pipe.

  • Consumable Insert. Preplaced filler metal which is completely fused into the root of the joint and becomes part of the weld.

  • Continuous-Welded Pipe. Furnace- welded pipe produced in continuous lengths from coiled skelp and subsequently cut into individual lengths, having its longitudinal butt joint forge- welded by the mechanical pressure developed in rolling the hot-formed skelp through a set of round pass welding rolls.

  • Contractor. The entity responsible for consumable insert ring in- furnishing materials and services for fabserted in pipe joint eccentrically for welding in fabrication and installation of piping and horizontal position.

  • Control Piping. All piping, valves, and fittings used to interconnect air, gas, or hydraulically operated control apparatus or instrument transmitters and receivers.

  • Controlled Cooling. A process of cooling from an elevated temperature in a predetermined manner to avoid hardening, cracking, or internal damage or to produce a desired metallurgical micro-structure. This cooling usually follows the final hot-forming or post heating operation.

  • Corner Joint. A joint between two members located approximately at right angles to each other in the form of an L.

  • Coupling. A threaded sleeve used to connect two pipes. Commercial couplings have internal threads to fit external threads on pipe.

  • Covered Electrode. A filler metal electrode, used in arc welding, consisting of a metal core wire with a relatively thick covering which provides protection for the molten metal from the atmosphere, improves the properties of the weld metal, and stabilizes the arc. Covered electrodes are extensively used in shop fabrication and field erection of piping of carbon, alloy, and stainless steels.

  • Crack. A fracture-type imperfection characterized by a sharp tip and high ratio of length and depth to opening displacement.

  • Creep or Plastic Flow of Metals. At sufficiently high temperatures, all metals flow under stress. The higher the temperature and stress, the greater the tendency to plastic flow for any given metal.

  • Cutting Torch. A device used in oxygen, air, or powder cutting for controlling and directing the gases used for preheating and the oxygen or powder used for cutting the metal.

  • Defect. A flaw or an imperfection of such size, shape, orientation, location, or properties as to be rejectable per the applicable minimum acceptance standards.

  • Density. The density of a substance is the mass of the substance per unit volume. It may be expressed in a variety of units.

  • Deposited Metal. Filler metal that has been added during a welding operation.

  • Depth of Fusion. The distance that fusion extends into the base metal from the surface melted during welding.

  • Designer. Responsible for ensuring that the engineering design of piping complies with the requirements of the applicable code and standard and any additional requirements established by the owner.

  • Dew Point. The temperature at which the vapor condenses when it is cooled at constant pressure.

  • Dilatant Liquid. If the viscosity of a liquid increases as agitation is increased at constant temperature, the liquid is termed dilatant. Examples are clay slurries and candy compounds.

  • Discontinuity. A lack of continuity or cohesion; an interruption in the normal physical structure of material or a product.

  • Double Submerged Arc-Welded Pipe. Pipe having a longitudinal butt joint produced by at least two passes, one of which is on the inside of the pipe. Coalescence is produced by heating with an electric arc or arcs between the bare metal electrode or electrodes and the work. The welding is shielded by a blanket of granular, fusible material on the work. Pressure is not used, and filler metal for the inside and outside welds is obtained from the electrode or electrodes.

  • Ductile Iron. A cast ferrous material in which the free graphite is in a spheroidal form rather than a fluke form. The desirable properties of ductile iron are achieved by means of chemistry and a ferritizing heat treatment of the castings.

  • Eddy Current Testing. This is a non-destructive testing method in which eddy current flow is induced in the test object. Changes in the flow caused by variations in the object are reflected into a nearby coil or coils for subsequent analysis by suitable instrumentation and techniques.

  • Edge Joint. A joint between the edges of two or more parallel or nearly parallel members.

  • Edge Preparation. The contour prepared on the edge of a member for welding.

  • Electric Flash-Welded Pipe. Pipe having a longitudinal butt joint in which coalescence is produced simultaneously.

  • Edge preparation. over the entire area of abutting surfaces by the heat obtained from resistance to the flow of electric current between the two surfaces and by the application of pressure after heating is substantially completed. Flashing and upsetting are accompanied by expulsion of metal from the joint.

  • Electric Fusion-Welded Pipe. Pipe having a longitudinal or spiral butt joint in which coalescence is produced in the preformed tube by manual or automatic electric arc welding. The weld may be single or double and may be made with or without the use of filler metal.

  • Electric Resistance-Welded Pipe. Pipe produced in individual lengths or in continuous lengths from coiled skelp and subsequently cut into individual lengths having a longitudinal butt joint in which coalescence is produced by the heat obtained from resistance of the pipe to the flow of electric current in a circuit of which the pipe is a part and by the application of pressure.

  • End Preparation. The contour prepared on the end of a pipe, fitting, or nozzle for welding. The particular preparation is prescribed by the governing code.

  • Engineering Design. The detailed design developed from process requirements and conforming to established design criteria, including all necessary drawings and specifications, governing a piping installation.

  • Equipment Connection. An integral part of such equipment as pressure vessels, heat exchanges, pumps, etc., designed for attachment of pipe or piping components.

  • Erection. The complete installation of a piping system, including any field assembly, fabrication, testing, and inspection of the system.

  • Erosion. Destruction of materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles.

  • Examination. The procedures for all visual observation and non-destructive testing.

  • Expansion Joint. A flexible piping component which absorbs thermal and/or terminal movement.

  • Extruded Nozzles. The forming of nozzle (tee) outlets in pipe by pulling hemi-spherically or conically shaped dies through a circular hole from the inside of the pipe. Although some cold extruding is done, it is generally performed on steel after the area to be shaped has been heated to temperatures between 2000 and 1600°F (1093 and 871°C).

  • Extruded Pipe. Pipe produced from hollow or solid round forgings, usually in a hydraulic extrusion press. In this process, the forging is contained in a cylindrical die. Initially a punch at the end of the extrusion plunger pierces the forging. The extrusion plunger then forces the contained billet between the cylindrical die and the punch to form the pipe, the latter acting as a mandrel. One variation of this process utilizes autofrettage (hydraulic expansion) and heat treatment, above the re-crystallization temperature of the material, to produce a wrought structure.

  • Fabrication. Primarily, the joining of piping components into integral pieces ready for assembly. It includes bending, forming, threading, welding, or other operations upon these components, if not part of assembly. It may be done in a shop or in the field.

  • Face of Weld. The exposed surface of a weld on the side from which the welding was done.

  • Filler Metal. Metal to be added in welding, soldering, brazing, or braze welding.

  • Fillet Weld. A weld of an approximately triangular cross section joining two surfaces approximately at right angles to each other in a lap joint, tee joint, corner joint, or socket weld.

  • Fire Hazard. Situation in which a material of more than average combustibility or excludability exists in the presence of a potential ignition source.

  • Flat-Land Bevel. A square extended root face preparation extensively used in inert-gas, root-pass welding of piping.

  • Flat Position. The position of welding which is performed from the upper side of the joint, while the face of the weld is approximately horizontal.

  • Flaw. An imperfection of unintentional discontinuity which is detectable by a non-destructive examination.

  • Flux. Material used to dissolve, prevent accumulation of, or facilitate removal of oxides and other undesirable substances during welding, brazing, or soldering.

  • Flux-Cored Arc Welding (FCAW). An arc welding process that employs a continuous tubular filler metal (consumable) electrode having a core of flux for shielding. Adding shielding may or may not be obtained from an externally supplied gas or gas mixture.

  • Forge Weld. A method of manufacture similar to hammer welding. The term forge welded is applied more particularly to headers and large drums, while hammer welded usually refers to pipe.

  • Forged and Bored Pipe. Pipe produced by boring or trepanning of a forged billet.

  • Full-Fillet Weld. A fillet weld whose size is equal to the thickness of the thinner member joined.

  • Fusion. The melting together of filler and base metal, or of base metal only, which results in coalescence.

  • Fusion Zone. The area of base metal melted as determined on the cross section of a weld.

  • Galvanizing. A process by which the Fusion zone is the section of surface of iron or steel is covered with the parent metal which melts during the weld a layer of zinc coating process.

  • Gas Metal Arc Welding (GMAW). An arc welding process that employs a contin- uous solid filler metal (consumable) electrode. Shielding is obtained entirely from an externally supplied gas or gas mixture.4,8 (Some methods of this process have been called MIG or CO2 welding.)

  • Gas Tungsten Arc Welding (GTAW). An arc welding process that employs a tungsten (nonconsumable) electrode. Shielding is obtained from a gas or gas mixture. Pressure may or may not be used, and filler metal may or may not be used. (This process has sometimes been called TIG welding.) When shielding is obtained by the use of an inert gas such as helium or argon, this process is called inert-gas tungsten arc welding.

  • Gas Welding. Welding process in which coalescence is produced by heating with a gas flame or flames, with or without the application of pressure and with or without the use of filler metal.

  • Groove. The opening provided for a groove weld.

  • Groove Angle. The total included angle of the groove between parts to be joined by a groove weld.

  • Groove Face. That surface of a member included in the groove.

  • Groove Radius. The radius of a J or U groove.

  • Groove Weld. A weld made in the groove between two members to be joined. The standard type of groove welds are square, single-V, single-bevel, single-U, single-J, double-V, double-U, double-bevel, double-J, and flat-land single, and double-V groove welds.

  • Hammer Weld. Method of manufacturing large pipe (usually NPS 20 or DN 500 and larger) by bending a plate into circular form, heating the overlapped edges to a welding temperature, and welding the longitudinal seam with a power hammer applied to the outside of the weld while the inner side is supported on an over- hung anvil.

  • Hangers and Supports. Hangers and supports include elements which transfer the load from the pipe or structural attachment to the supporting structure or equipment. They include hanging-type fixtures such as hanger rods, spring hangers, sway braces, counterweights, turnbuckles, struts, chains, guides, and anchors and bearing-type fixtures such as saddles, bases, rollers, brackets, and sliding supports.

  • Header. A pipe or fitting to which a number of branch pipes are connected.

  • Heat-Affected Zone. That portion of the base metal which has not been melted but whose mechanical properties or micro-structure has been altered by the heat of welding or cutting.

  • Heat Fusion Joint. A joint made in thermoplastic piping by heating the parts sufficiently to permit fusion of the materials when the parts are pressed together.

  • Horizontal Fixed Position. In pipe welding, the position of a pipe joint in which the axis of the pipe is approximately horizontal and the pipe is not rotated during the operation.

  • Horizontal-Position Fillet Weld. Welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface.

  • Horizontal-Position Groove Weld. The position of welding in which the weld axis lies in an approximately horizontal plane and the face of the weld lies in an approximately vertical plane.

  • Horizontal Rolled Position. The position of a pipe joint in which welding is performed in the flat position by rotating the pipe.

  • Hot Bending. Bending of piping to a predetermined radius after heating to a suitably high temperature for hot working. On many pipe sizes, the pipe is firmly packed with sand to avoid wrinkling and excessive out-of-roundness.

  • Hot Taps. Branch piping connections made to operating pipelines, mains, or other facilities while they are in operation.

  • Hot Working. The plastic deformation of metal at such a temperature and rate that strain hardening does not occur. Extruding or swaging of chromemoly piping at temperatures between 2000 and 1600°F (1093 and 871°C) would be considered hot-forming or hot-working operations.

  • Hydraulic Radius. The ratio of area of flowing fluid to the wetted perimeter.

  • Impact Test. A test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension, or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in Charpy or Izod tests.

  • Imperfection. A condition of being imperfect; a departure of a quality characteristic from its intended condition.

  • Incomplete Fusion. Fusion which is less than complete and which does not result in melting completely through the thickness of the joint.

  • Indication. The response or evidence from the application of a nondestructive examination.

  • Induction Heating. Heat treatment of completed welds in piping by means of placing induction coils around the piping. This type of heating is usually performed during field erection in those cases where stress relief of carbon and alloy-steel field welds is required by the applicable code.

  • Inspection. Activities performed by an authorized inspector to verify whether an item or activity conforms to specified requirements.

  • Instrument Piping. All piping, valves, and fittings used to connect instruments to main piping, to other instruments and apparatus, or to measuring equipment.

  • Interpass Temperature. In a multiple-pass weld, the minimum or maximum temperature of the deposited weld metal before the next pass is started.

  • Interrupted Welding. Interruption of welding and preheat by allowing the weld area to cool to room temperature as generally permitted on carbon-steel and on chromemoly alloy-steel piping after sufficient weld passes equal to at least one- third of the pipe wall thickness or two weld layers, whichever is greater, have been deposited.

  • Joint. A connection between two lengths of pipe or between a length of pipe and a fitting.

  • Joint Penetration. The minimum depth a groove weld extends from its face into a joint, exclusive of reinforcement.

  • Kinematic Viscosity. The ratio of the absolute viscosity to the mass density.

  • Weld joint penetration. In the metric system, kinematic viscosity is measured in strokes or square centimeters per second.

  • Laminar Flow. Fluid flow in a pipe is usually considered laminar if the Reynolds number is less than 2000. Depending upon many possible varying conditions, the flow may be laminar at a Reynolds number as low as 1200 or as high as 40,000; however, such conditions are not experienced in normal practice.

  • Lap Weld. Weld along a longitudinal seam in which one part is overlapped by the other. A term used to designate pipe made by this process.

  • Lapped Joint. A type of pipe joint made by using loose flanges on lengths of pipe whose ends are lapped over to give a bearing surface for a gasket or metal-to- metal joint.

  • Liquid Penetrant Examination or Inspection. This is a non-destructive examination method for finding discontinuities that are open to the surface of solid and essentially nonporous materials. This method is based on capillary action or capillary attraction by which the surface of a liquid in contact with a solid is elevated or depressed. A liquid penetrant, usually a red dye, is applied to the clean surface of the specimen. Time is allowed for the penetrant to seep into the opening. The excess penetrant is removed from the surface. A developer, normally white, is applied to aid in drawing the penetrant up or out to the surface. The red penetrant is drawn out of the discontinuity, which is located by the contrast and distinct appearance of the red penetrant against the white background of the developer.

  • Local Preheating. Preheating of a specific portion of a structure.

  • Local Stress-Relief Heat Treatment. Stress-relief heat treatment of a specific portion of a weldment. This is done extensively with induction coils, resistance coils, or propane torches in the field erection of steel piping.

  • Machine Welding. Welding with equipment which performs the welding operation under the observation and control of an operator. The equipment may or may not perform the loading and unloading of the work.

  • Magnetic Particle Examination or Inspection. This is a non-destructive examination method to locate surface and subsurface discontinuities in ferromagnetic materials. The presence of discontinuities is detected by the use of finely divided ferromagnetic particles applied over the surface. Some of these magnetic particles are gathered and held by the magnetic leakage field created by the discontinuity. The particles gathered at the surface form an outline of the discontinuity and generally indicate its location, size, shape, and extent.

  • Malleable Iron. Cast iron which has been heat-treated in an oven to relieve its brittleness. The process somewhat improves the tensile strength and enables the material to stretch to a limited extent without breaking.

  • Manual Welding. Welding wherein the entire welding operation is performed and controlled by hand.

  • Mean Velocity of Flow. Under steady state of flow, the mean velocity of flow at a given cross section of pipe is equal to the rate of flow Q divided by the area of cross section A. It is expressed in feet per second or meters per second.

where v = mean velocity of flow, in feet per second, ft/s (meters per second, m/s)

Q = rate of flow, in cubic feet per second, ft3 /s (cubic meters per second, m3 /s)

A = area of cross section, in square feet, ft2 (square meters, m2)

  • Mechanical Joint. A joint for the purpose of mechanical strength or leak resistance or both, where the mechanical strength is developed by threaded, grooved, rolled, flared, or flanged pipe ends or by bolts, pins, and compounds, gaskets, rolled ends, caulking, or machined and mated surfaces. These joints have particular application where ease of disassembly is desired.

  • Mill Length. Also, known as random length. The usual run-of-mill pipe is 16 to 20 ft (5 to 6 m) in length. Line pipe and pipe for power plant use are sometimes made in double lengths of 30 to 35 ft (10 to 12 m).

  • Miter. Two or more straight sections of pipe matched and joined on a line bisecting the angle of junction so as to produce a change in direction.4

  • Newtonian Liquid. A liquid is called newtonian if its viscosity is unaffected by the kind and magnitude of motion or agitation to which it may be subjected, as long as the temperature remains constant. Water and mineral oil are examples of n