INTRODUCTION
Piping systems are like arteries and veins. They carry the lifeblood of modern civilization. In a modern city they transport water from the sources of water supply to the points of distribution; convey waste from residential and commercial buildings and other civic facilities to the treatment facility or the point of discharge. Similarly, pipelines carry crude oil from oil wells to tank farms for storage or to refineries for processing. The natural gas transportation and distribution lines convey natural gas from the source and storage tank forms to points of utilization, such as power plants, industrial facilities, and commercial and residential communities. In chemical plants, paper mills, food processing plants, and other similar industrial establishments, the piping systems are utilized to carry liquids, chemicals, mixtures, gases, vapors, and solids from one location to another. The fire protection piping networks in residential, commercial, industrial, and other buildings carry fire suppression fluids, such as water, gases, and chemicals to provide protection of life and property. The piping systems in thermal power plants convey high-pressure and high-temperature steam to generate electricity. Other piping systems in a power plant transport high- and low-pressure water, chemicals,
low-pressure steam, and condensate. Sophisticated piping systems are used to process and carry hazardous and toxic substances. The storm and wastewater piping systems transport large quantities of water away from towns, cities, and industrial and similar establishments to safeguard life, property, and essential facilities. In health facilities, piping systems are used to transport gases and fluids for
medical purposes. The piping systems in laboratories carry gases, chemicals, vapors, and other fluids that are critical for conducting research and development. In short, the piping systems are an essential and integral part of our modern civilization just as arteries and veins are essential to the human body.
The design, construction, operation, and maintenance of various piping systems involve understanding of piping fundamentals, materials, generic and specific design considerations, fabrication and installation, examinations, and testing and inspection requirements, in addition to the local, state and federal regulations.
PIPING
Piping includes pipe, flanges, fittings, bolting, gaskets, valves, and the pressure containing portions of other piping components. It also includes pipe hangers and supports and other items necessary to prevent over pressurization and over stressing of the pressure-containing components. It is evident that pipe is one element or a part of piping. Therefore, pipe sections when joined with fittings, valves, and other mechanical equipment and properly supported by hangers and supports, are called piping.
PIPE
Pipe is a tube with round cross section conforming to the dimensional requirements of
- ASME B36.10M Welded and Seamless Wrought Steel Pipe
- ASME B36.19M Stainless Steel Pipe
PIPE SIZE
Initially a system known as iron pipe size (IPS) was established to designate the pipe size. The size represented the approximate inside diameter of the pipe in inches. An IPS 6 pipe is one whose inside diameter is approximately 6 inches (in). Users started to call the pipe as 2-in, 4-in, 6-in pipe and so on. To begin, each pipe size was produced to have one thickness, which later was termed as standard (STD) or standard weight (STD. WT.). The outside diameter of the pipe was standardized. As the industrial requirements demanded the handling of higher-pressure fluids, pipes were produced having thicker walls, which came to be known as extra strong (XS) or extra heavy (XH). The higher pressure requirements increased further, requiring thicker wall pipes. Accordingly, pipes were manufactured with double extra strong (XXS) or double extra heavy (XXH) walls while the standardized outside diameters are unchanged.
With the development of stronger and corrosion-resistant piping materials, the need for thinner wall pipe resulted in a new method of specifying pipe size and wall thickness. The designation known as nominal pipe size (NPS) replaced IPS, and the term schedule (SCH) was invented to specify the nominal wall thickness of pipe.
Nominal pipe size (NPS) is a dimensionless designator of pipe size. It indicates standard pipe size when followed by the specific size designation number without an inch symbol. For example, NPS 2 indicates a pipe whose outside diameter is 2.375 in. The NPS 12 and smaller pipe has outside diameter greater than the size designator (say, 2, 4, 6, . . .). However, the outside diameter of NPS 14 and larger pipe is the same as the size designator in inches. For example, NPS 14 pipe has an outside diameter equal to 14 in. The inside diameter will depend upon the pipe wall thickness specified by the schedule number. Refer to ASME B36.10M or ASME B36.19M. Refer to App. E2 or E2M.
Diameter nominal (DN) is also a dimensionless designator of pipe size in the metric unit system, developed by the International Standards Organization (ISO). It indicates standard pipe size when followed by the specific size designation number
Pipe Wall Thickness
Schedule is expressed in numbers (5, 5S, 10, 10S, 20, 20S, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160). A schedule number indicates the approximate value of the expression 1000 P/S, where P is the service pressure and S is the allowable stress, both expressed in pounds per square inch (psi). The higher the schedule number, the thicker the pipe is. The outside diameter of each pipe size is standardized. Therefore, a particular nominal pipe size will have a different inside diameter depending upon the schedule number specified.
Note that the original pipe wall thickness designations of STD, XS, and XXS have been retained; however, they correspond to a certain schedule number depending upon the nominal pipe size. The nominal wall thickness of NPS 10 and smaller schedule 40 pipe is same as that of STD. WT. pipe. Also, NPS 8 and smaller schedule 80 pipe has the same wall thickness as XS pipe. The schedule numbers followed by the letter S are per ASME B36.19M, and they are primarily intended for use with stainless steel pipe. The pipe wall thickness specified by a schedule number followed by the letter S may or may not be the same as that specified by a schedule number without the letter S. Refer to ASME B36.19M and ASME B36.10M.10,11
ASME B36.19M does not cover all pipe sizes. herefore, the dimensional requirements of ASME B36.10M apply to stainless steel pipe of the sizes and schedules not covered by ASME B36.19M.
PIPING CLASSIFICATION
It is usual industry practice to classify the pipe in accordance with the pressure temperature rating system used for classifying flanges. However, it is not essential
French equivalent of pressure nominal.
In addition, the piping may be classified by class ratings covered by other ASME standards, such as ASME B16.1, B16.3, B16.24, and B16.42. A piping system may be rated for a unique set of pressures and temperatures not covered by any standard.
Pression nominal (PN) is the rating designator followed by a designation number, which indicates the approximate pressure rating in bars. The bar is the unit of pressure, and 1 bar is equal to 14.5 psi or 100 kilopascals (kPa). Table A1.2 provides a cross-reference of the ASME class ratings to PN rating designators. It is evident that the PN ratings do not provide a proportional relationship between different PN numbers, whereas the class numbers do. Therefore, it is recommended that class numbers be used to designate the ratings. Refer to Chap. B2 for a more detailed discussion of class rating of piping systems.
GENERAL DEFINITIONS
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. Refer to Chap. B8 of this handbook.
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
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
- Molybdenum
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 operator. The equipment may or may not perform the loading and unloading of the work.3,5
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. See Fig. A1.1.
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. See Fig. A1.2.
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 action.
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. See Fig. A1.3.
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. Replaced filler metal which is completely fused into the root of the joint and becomes part of the weld. See Fig. A1.4.
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 furnishing materials and services for fabrication and installation of piping and associated equipment.
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. See Fig. A1.5.
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. See Fig. A1.6.
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 nondestructive 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. See Fig. A1.7.
Electric Flash-Welded Pipe. Pipe having a longitudinal butt joint in which coalescence is produced simultaneously 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.
Electrode. See Covered Electrode.
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. Refer to Chap. A6 of this handbook.
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 exchangers, 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 nondestructive 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 hemispherically 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 auto frettage (hydraulic expansion) and heat treatment, above the recrystallization 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.5 See Fig. A1.8.
Fire Hazard. Situation in which a material of more than average combustibility or explodibility 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. See Fig. A1.9
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. See Fig. A1.10.
Flaw. An imperfection of unintentional discontinuity which is detectable by a nondestructive 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. See Fig. A1.11.
Galvanizing. A process by which the surface of iron or steel is covered with a layer of zinc.
Gas Metal Arc Welding (GMAW ). An arc welding process that employs a continuous 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 (non consumable) 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. See Fig. A1.12.
Groove Face. That surface of a member included in the groove. See Fig. A1.13.
Groove Radius. The radius of a J or U groove. See Fig. A1.14.
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. See Fig. A1.15 for a typical groove weld.
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 overhung 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. See Fig. A1.16.
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. See Fig. A1.17.
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. See Fig. A1.18.
Horizontal Rolled Position. The position of a pipe joint in which welding is performed in the flat position by rotating the pipe. See Fig. A1.19.
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 chrome-moly 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
Root Edge. A root face of zero width.
Root Face. That portion of the groove face adjacent to the root of the joint. This portion is also referred to as the root land. See Fig. A1.21.
Single-Bevel-, Single-J, Single-U, Single-V-Groove Welds. All are specific types of groove welds and are illustrated in Fig. A1.22.
Single-Welded Butt Joint. A butt joint welded from one side only.
Size of Weld. For a groove weld, the joint penetration, which is the depth of chamfering plus the root penetration. See Fig. A1.21. For fillet welds, the leg length of the largest isosceles right triangle which can be inscribed within the fillet-weld cross section. See Fig. A1.23.
Welding Rod. Filler metal, in wire or rod form, used in gas welding and brazing procedures and those arc welding processes where the electrode does not furnish the filler metal.
Welding Sequence. The order of making the welds in a weldment.
Weldment. An assembly whose component parts are to be joined by welding.
Wrought Iron. Iron refined in a plastic state in a puddling furnace. It is characterized by the presence of about 3 percent of slag irregularly mixed with pure iron and about 0.5 percent carbon and other elements in solution.
Wrought Pipe. The term wrought pipe refers to both wrought steel and wrought iron. Wrought in this sense means ‘‘worked,’’ as in the process of forming furnace welded pipe from skelp or seamless pipe from plates or billets. The expression wrought pipe is thus used as a distinction from cast pipe. Wrought pipe in this sense should not be confused with wrought-iron pipe, which is only one variety of wrought pipe. When wrought-iron pipe is referred to, it should be designated by its complete name.
