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Pipe Fittings

The major piping materials are also produced in the form of standard fittings. Among the more widely used materials are ductile or cast iron, malleable iron, brass, copper, cast steel, forged steel, and wrought steel. Other major nonferrous piping materials are also produced in the form of cast and wrought fittings. Ductile and cast-iron fittings are made by conventional foundry methods for a variety of joints including bell-and-spigot, push-on flanged, and mechanical (gland-type) or other proprietary designs.

Ductile and Cast-Iron Fittings

Cast-iron fittings are covered by a number of ASME and ANSI/AWWA standards:

  • ASME B16.1 Cast Iron Pipe Flanges and Flanged Fittings, Class 25, 125, 250, and 800 (The standard also includes bolt, nut, and gasket data.)

  • ASME B16.4 Gray Iron Threaded Fittings, Class 125 and 250

  • ASME B16.12 Cast Iron Threaded Drainage Fittings ANSI/AWWA C110/A21.10 Ductile Iron and Gray Iron Fittings, 3-in through 48-in (76 mm through 6200 mm), for Water and Other Liquids

  • ANSI/AWWA C115/A21.15 Ductile Iron and Gray Iron Fittings, 3-in through 48-in (76 mm through 1200 mm), for Water

  • ANSI/AWWA C153/A21.53 Ductile Iron Compact Fittings, 3-in through 24-in (76 mm through 610 mm) and 54-in through 64-in (1400 mm through 1600 mm), for Water Service

Cast-Iron Threaded Fittings

Cast-iron threaded fittings are covered by ASME Standard B16.4. The standard specifies the below-listed attributes for Class 125 and Class 250 tees, crosses, 45° and 90° elbows, reducing tees, caps, couplings, and reducing couplings in sizes ranging from NPS ¹⁄₄ (DN 6) through NPS 12 (DN 300), inclusive. However, in Class 250, the standard only covers 45° and 90° elbows, straight tees, and straight crosses.

  • Pressure-temperature ratings

  • Size and method of designating openings of reducing fittings

  • Marking

  • Minimum requirements for materials

  • Dimensions and tolerances

  • Threading

  • Coatings

Pressure-Temperature Rating of ANSI-ASME B16.4 Cast-Iron Fittings

The pressure-temperature ratings of Class 125 and Class 250 are listed in Table A2.2. The ratings are independent of the contained fluid and are the maximum non-shock pressure at the listed temperature. As a minimum, the material must conform to class A of ASTM A126. The fittings are threaded with ASME B1.20.1 pipe threads.

Malleable-Iron Threaded Fittings

Malleable-iron fittings are also extensively produced. They are generally made with threaded joints. Malleable-iron threaded fittings for Classes 150 and 300 are standardized in ASME B16.3. The standard specifies the same attributes for Class 150 and 300 fittings as discussed under ASME B16.4 for gray-iron fittings. The fittings are available in a variety of configurations from NPS ¹⁄₈ (DN 3) through NPS 6 (DN 150). The pressure-temperature ratings of these fittings are listed in Table A2.3. As with cast-iron fittings, the ratings are independent of the contained fluid and are maximum nonshock pressures at the listed temperatures. Malleable- iron fittings are furnished black, galvanized, or as otherwise ordered by the buyer. The galvanized threaded fittings commonly used in water piping for homes are Class 150 malleable iron. Minimum properties of malleable iron are required to meet ASTM A197 Cupola Malleable Iron requirements. The fittings are threaded with ASME B1.20.1 pipe threads.

Pressure-Temperature Rating of ASME B16.3 Malleable-Iron Threaded Fittings

Cast-Brass and Cast-Bronze Threaded Fittings

Cast-brass and -bronze threaded fittings are commonly produced for use with brass pipe. The fittings are manufactured in accordance with ASME B16.15 in pressure Classes 125 and 250. The standard establishes pressure-temperature ratings, size and method of designating openings of reducing fittings, marking, minimum require- ments for casting quality, and materials. The nonshock pressure-temperature ratings are listed in Table A2.4. The permitted materials for the fittings are:

  • ASTM B62, alloy C83600

  • ASTM B584, alloy C83800 and C84400

  • ASTM B16, alloy C36000 (bar stock)

  • ASTM B140, alloy C32000 or C31400 (bar stock)

Pressure-Temperature Rating for Classes 125 and 250 Cast-Bronze Threaded Fittings (ANSI-ASME B16.15-1985)

Soldered-Joint Fittings

Soldered-joint wrought metal and cast-brass or -bronze fittings for use with copper water tubes are covered by ASTM B88 and H23.1. The fittings are made in accordance with ASME B16.22 and B16.18, respectively. Joints using these types of fittings and made with 50–50 tin-lead solder, 95-tin 5-antimony solder, or solder melting above 1100°F (593°C) have the pressure-temperature ratings shown in Table A2.5. (Note: Lead-bearing solder is not permitted for potable water service.)

Wrought copper fittings normally have a minimum copper content of 83 percent. Cast-brass fittings conform to ASTM B62 and have a nominal composition of 85 percent copper, 5 percent tin, 5 percent lead, and 5 percent zinc. The minimum requirements for 50–50 tin-lead solder generally used with these fittings are covered in ASTM B32 alloy grade 50A. Metal thickness tolerances and general dimensions of fittings are given in ASME B16.18.

Pressure Ratings for Solder Joints (ASME B16.18-1984). Maximum Working Pressure (psi)

Cast-Iron Flanged Fittings

Cast-iron flanged fittings are produced in accordance with ASME B16.1. The standard specifies pressure-temperature ratings, sizes, marking, minimum requirements for materials, dimensions and tolerances, bolting, gasketing, and testing requirements. The fittings are manufactured in a variety of configurations (tees, elbows, crosses, laterals, etc.) in pressure Classes 25, 125, 250, and 800. Not all sizes and styles are available in all ratings. The sizes available in each class are listed below:

piping pressure class

Cast- and Forged-Steel and Nickel-Alloy Flanged Fittings

Flanged fittings of steel and nickel alloys are manufactured in accordance with ASME B16.5. The standard covers ratings, materials, dimensions, tolerances, mark- ing, testing, and methods of designating openings for pipe flanges and flanged fittings in sizes NPS ¹⁄₂ (DN 15) through NPS 24 (DN 600) and in rating Classes 150, 300, 400, 600, 900, 1500, and 2500. However, not all sizes are available in all pressure classes. The standard also contains recommendations and requirements for bolting and gaskets.

Within each pressure class, the dimensions of the fittings are held constant, irrespective of the materials being used. Since the physical properties of different materials vary, the pressure-temperature ratings within each pressure class vary with the material. As an example, a Class 600 forged carbon steel (A105) flange is rated at 1270 psig at 400°F, whereas a Class 600 forged stainless steel (A182, F304) flange is rated at 940 psig at 400°F. The matrix of materials and pressure classes is too numerous to reproduce here; therefore, the reader is referred to ASME B16.5 for the flanged fitting pressure-temperature ratings.

Forged-Steel Threaded and Socket-Welding Fittings

Forged-steel socket welding and threaded fittings are manufactured in accordance with ASME B16.11. The standard covers pressure-temperature ratings, dimensions, tolerances, marking, and material requirements for forged carbon and alloy steel fittings in the styles and sizes.Acceptable material forms are forgings, bars, seamless pipe, and seamless tubes which conform to the chemical compositions, melting practices, and mechanical property requirements of ASTM A105, A182, or A350. Threaded fittings are available in pressure Classes 2000, 3000, and 6000. Socket- welded fittings are available in pressure Classes 3000, 6000, and 9000. Limitations on fitting size and service conditions are as provided for by the code governing the installation. The maximum allowable pressure of the fitting is equal to that computed for straight seamless pipe of equivalent material, considering manufacturing tolerance, corrosion allowance, and mechanical strength allowance. Also, for socket- welding fittings, the pressure rating must be matched to the pipe wall thickness to ensure that the flat of the band can accommodate the size of the fillet weld required by the applicable code.

Wrought-Steel Butt-Welding Fittings

Wrought-steel welding fittings include elbows, tees, crosses, reducers, laterals, lap- joint stub ends, caps, and saddles.

Wrought-steel fittings are made to the dimensional requirements of ASME B16.9 in sizes NPS ¹⁄₂ (DN 15) through NPS 48 (DN 1200). Also, short-radius elbows and returns are produced in accordance with ASME B16.28 in sizes NPS ¹⁄₂ (DN 15) through NPS 24 (DN 600). The wrought fitting materials conform to ASTM A234, A403, or A420, the grades of which have chemical and physical properties equivalent to that of the mating pipe. ASME B16.9 requires that the pressure-temperature rating of the fitting equal or exceed that of the mating pipe of the same or equivalent material, same size, and same nominal wall thickness. The pressure-temperature rating may be established by analysis or by proof testing. Short-radius elbows and returns (fitting centerline bend radius is equal to the fitting NPS) manufactured under ASME B16.28 are rated at 80 percent of the rating calculated for seamless straight pipe of the same size and nominal thickness and same or equivalent material. Therefore, both standards require that, in lieu of specifying any pressure rating, the pipe wall thickness and pipe material type with which the fittings are intended to be used be identified on the fitting.

Pressure testing of the fittings is not required by either standard. However, the fittings are required to be capable of withstanding, without leakage, a test pressure equal to that prescribed in the specification of the pipe with which the fitting is recommended to be used.

Both ASME B16.9 and B16.28 prescribe dimensions and manufacturing toler- ances of wrought butt-welded fittings. The standards establish laying dimensions, which remain fixed for each size and type of fitting irrespective of the fitting wall thickness. Laterals are not governed by any national standard.

Forged Branch Fittings

Under the various pressure piping codes, branch connections may be made by welding the branch pipe or a welding outlet fitting to the run pipe, provided sufficient reinforcement is available to compensate for the material removed from the run pipe to create the branch opening. The reinforcement may be in the form of excess material already available in the run and branch pipes, or it may be added. At the writing of this book, national standards governing the dimensions, tolerances, and manufacture of welding outlet fittings had not been issued. However, MSS-SP-97, 1995, has been developed to cover forged-carbon-steel 90° branch outlet fittings in butt-welding, socket-welding, and threaded outlet ends. The standard provides essential dimensions, finish, tolerances, and testing requirements. Because of the absence of strict standards, manufacturers produce welding outlet fittings of their own proprietary designs. These fittings must comply with the codes governing the systems in which the fittings are to be installed. The fittings, when installed in accordance with the manufacturers’ recommendations, include the required reinforcement. The dimensions of these fittings vary; standardized dimensions and properties must be obtained from the manufacturers. Also, designers must consider the appropriate parameters (e.g., stress intensification factors). The fittings are produced in carbon and alloy steels under the ASTM specifications for forgings permitted by applicable codes. #Little_PEng


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