Related Commercial Resources CHAPTER 22 Licensed for single user. © 2021 ASHRAE, Inc. PIPE DESIGN FUNDAMENTALS................................................................... 22.1 Codes and Standards ............................................................... 22.1 Design Considerations............................................................. 22.1 General Pipe Systems .............................................................. 22.1 Design Equations ..................................................................... 22.5 Sizing Procedure.................................................................... 22.10 Pipe-Supporting Elements ..................................................... 22.10 Pipe Expansion and Flexibility.............................................. 22.11 Pipe Bends and Loops............................................................ 22.12 PIPE AND FITTING MATERIALS........................................ 22.14 Pipe ........................................................................................ 22.14 Fittings ................................................................................... 22.18 Joining Methods ..................................................................... 22.18 Expansion Joints and Expansion Compensating Devices...... 22.20 APPLICATIONS..................................................................... 22.22 Water Piping .......................................................................... 22.22 Service Water Piping.............................................................. 22.23 Steam Piping .......................................................................... 22.29 Low-Pressure Steam Piping................................................... 22.30 Steam Condensate Systems .................................................... 22.32 Gas Piping.............................................................................. 22.35 Fuel Oil Piping....................................................................... 22.36 T • Pressure and temperature of the fluid. • External environment of the pipe: outdoor installations deal with temperature extremes, environmental contaminants, and ultraviolet radiation. Other environments could contain caustic chemicals. Soil can contain elements that can be corrosive to underground pipe systems. • Installation cost. • Pipe’s resistance to chemical attack from the fluid. HIS CHAPTER discusses pipe systems, materials, design, installation, supports, stress calculations, pipe expansion and flexibility, bends and loops, and application of pipe systems commonly used for heating, air conditioning, refrigeration, and service water. When selecting and applying components; applicable local codes, state or provincial codes, and voluntary industry standards (some of which have been adopted by code jurisdictions) must be followed. Further details on specific piping systems can be found in application-specific chapters of the ASHRAE Handbook. 1. FUNDAMENTALS 1.1 CODES AND STANDARDS The following organizations in the United States issue codes and standards for piping systems and components: ASME ASTM NFPA ICC MSS American Society of Mechanical Engineers American Society for Testing and Materials National Fire Protection Association International Code Council Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. AWWA American Water Works Association Parallel federal specifications also have been developed by government agencies and are used for many public works projects. Chapter IV of ASME Standard B31.9 lists applicable U.S. codes and standards for HVAC piping. In addition, it gives requirements for safe design and construction of piping systems for building heating and air conditioning. ASME Standard B31.5 gives similar requirements for refrigerant piping. 1.2 DESIGN CONSIDERATIONS Pipes are conduits in which fluids [compressible (e.g., air, steam) and noncompressible (e.g., water)] flow in a system, in response to a pressure differential. Piping system designers should assess the following aspects: • Code requirements. • Load: the amount of energy or fluid to be moved through the pipe to where it is needed; determination of load is not covered in this chapter (see Chapters 16 to 18 for information on load calculations). • Working fluid and fluid properties in the pipe. The preparation of this chapter is assigned to TC 6.1, Hydronic and Steam Equipment and Systems. 22.1 Copyright © 2021, ASHRAE When designing a fluid flow system, two related but distinct concerns emerge: sizing the pipe and determining the flow/pressure relationship. The two are often confused because they can use the same equations and design tools. Nevertheless, they should be determined separately. This chapter focuses on sizing the pipe during the design phase, and to this end presents design charts and tables for specific fluids in addition to the equations that describe fluid flow in pipes. Once a system has been sized, it should be analyzed with more detailed methods of calculation to determine the pump pressure, if applicable, required to achieve the desired flow. Computerized methods are well suited to handling the details of calculating losses around an extensive system. Not discussed in detail in this chapter, but of potentially great importance, are physical and chemical considerations such as pipe and fitting design; materials; and joining methods appropriate for working pressures and temperatures encountered, as well as resistance to chemical attack by the fluid. For more information, see Eshbach (2009), Heald (2002), and Nayyar (1999). For fluids not included in this chapter or for piping materials of different dimensions, manufacturers’ literature frequently supplies pressure drop charts. The Darcy-Weisbach equation, with the Moody chart or Colebrook equation, can be used as an alternative to pressure drop charts or tables. 1.3 GENERAL PIPE SYSTEMS Metallic Pipe Systems Each HVAC system and, under some conditions, portions of a system require a study of the conditions of operation to determine suitable materials. For example, because the static pressure of water in a high-rise building is higher in the lower levels than in the upper levels, a heavier pipe or different materials may be required for different vertical zones. Table 1 lists some typical systems and materials used for heating and air-conditioning metallic piping. The list is not all inclusive, because piping systems are constantly being developed. The pressure and temperature rating of each component selected must be 22.2 2021 ASHRAE Handbook—Fundamentals (SI) Table 1 Application Size, mm Chilled water Common Applications of Pipe, Fittings, and Valves for Heating and Air Conditioning Material Type 51 Steel Type F (CW) Schedule 40 62.5 to 305 Steel A or B, Type E Schedule 40 (ERW) Joint Type Fitting Material Thread Weld Flange Cast iron Wrought steel Wrought steel Cast iron Cast iron Wrought or cast Cu Copper, hard or soft Type K or L Licensed for single user. © 2021 ASHRAE, Inc. Copper, hard 10 to 25 PEX (barrier) 13 to 152 PE Heating and 51 and recirculating smaller 6 to 305 Steel Type F (CW) Steel B Type E (ERW) Steam and condensate Copper, hard Schedule 40 Schedule 40 Type M 10 to 25 PEX (barrier) SDR-9 51 and smaller Steel Type F (CW) or S Schedule 40d Steel B Type E (ERW) or S Schedule 40d Steel B Type E (ERW) or S Schedule 80 51 to 305 Steel B Type E (ERW) or S 125 Standard 150 125 250 Solder Flared (soft) Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Type M Solder Wrought or cast Cu Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld SDR-9 Crimp Bronze Clamp Brass Expansion Copper Compression Engineered plastic Push fit Proprietary Schedule 40,f 80, Thermal fusion, PE SDR compression Copper, hard or soft Type K or L 6 to 305 Systemg Class (When Temperature, Maximum Pressure at Applicable) °C Temperature,a,b kPa Schedule 40 Thread Weld Flange Cast iron Wrought steel Wrought steel Cast iron Cast iron Wrought or cast Cu 862 2758 1724 1207 2758 2586 Type K soft 4378 Type K hard 1724 Type L soft 2999 Type L hard 38 38 1724 Type L soft 2586 Type K soft 2724 Type M hard 38 1586 Type M soft 23 1000 49 (60 limit for Varies with pipe wall thickness, some applica- grade, schedule, size. Check manutions) facturer’s documentation for design ratings 207 to 758 at 54°C 125 Standard 150 125 250 Solder Braze Flared (soft) Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Solder Wrought or cast Cu Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Crimp Bronze Clamp Brass Expansion Copper Compression Engineered plastic Push fit Proprietary Thread Thread Socket Thread Thread Socket Thread Socket Thread Socket Weld Flange 121 121 121 121 121 38 121 121 121 121 121 93 862 2758 1724 862 2758 2069 Type K soft 4378 Type K hard 1413 Type L soft 2999 Type L hard 93 93 2069 Type K soft 1413 Type L soft 2724 Type M hard 93 1379 Type M soft 93 545 Cast iron Malleable iron Forged steel Cast iron Malleable iron Forged steel Cast iron 125 150 3000 125 150 3000 250 621 621 621 690 862 2758 1379 Malleable iron Forged steel Wrought steel Wrought steel 300 3000 Standard 150 1724 2758 1724 1379 Pipe Design Table 1 Application Size, mm Common Applications of Pipe, Fittings, and Valves for Heating and Air Conditioning (Continued) Material Type Joint Type Fitting Material Systemg Class (When Temperature, Maximum Pressure at Applicable) °C Temperature,a,b kPa 125 XS 300 250 Steel B Type E (ERW) or S Schedule 80 Weld Flange Cast iron Wrought steel Wrought steel Cast iron Ground6 to 51 source heat pump 10 to 25 Copper, hard or soft PEX (barrier) Type L or ACR Flared or brazed Wrought or cast Cu 93 SDR-9 Crimp Clamp Expansion Compression Push fit Proprietary Bronze Brass Copper Engineered plastic 82 Refrigerant Schedule 40 Weld 10 to 105 Steel B Type E (ERW) Copper, hard Type L or ACR Braze 6 to 305 Copper, hard or soft Type K or L Natural gas and LP Licensed for single user. © 2021 ASHRAE, Inc. 22.3 Wrought or Forged Cu 93 2999 Type L hard, 4655 ACR soft Solder Wrought or cast Cu Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanically formed Braze Wrought or cast Cu Weld Solder Wrought or cast Cu Braze Wrought or cast Cu Crimp Bronze Clamp Brass Expansion Copper Compression Engineered plastic Push fit Proprietary Thermal fusion, PE compression 38 2551 Type K soft 4378 Type K hard 1724 Type L soft 2999 Type L hard 38 2551 Type K soft 1724 Type L soft 3448 Type ACR hard 2000 Type ACR Soft 1000 Copper, hard ACR 10 to 25 PEX SDR-9 13 to 152 PE Schedule 40, 80, SDR 13 to 152 HDPE SDR Thermal fusion, compression HDPE Black Steel, B Type E (ERW) or S (seamless) Schedule 40 Thread or weld Copper, hard or soft Type K or L Black malleable iron 150 Wrought steel weld Forged steel flanges 150 Wrought or cast Cu 6 to 305 Copper, hard 6 to 305 ABS 13 to 152 HDPE Compressed 62.5 and air smaller 62.5 10 to 105 13 to 102 1413 Type L soft, 2999 Type L hard, 4655 ACR soft, 3448 ACR hard 690 Wrought steel 10 to 105 Fuel oil, 51 to 305 aboveground 690 4826 3448 1379 Solder Flared (soft) Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze or weld Wrought or cast Cu Type M Solder Wrought or cast Cu Braze Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed ABS Schedule 40,f 80, Solvent weld, thread, SDR flange SDR-9 Thermal fusion, HDPE compression 38 38 23 49 (60limit for Depends on pipe, grade, schedule, some applica- size. Generally 207 to 758 at 54°C tions) 49 Depends on pipe, grade, schedule, size. Generally 441 for SDR 11 at 49°C 38 2069 Type K soft 4378 Type K hard 1724 Type L soft 2999 Type L hard 38 38 2069 Type K soft, 1724 Type L soft 2724 Type M hard 71 limit Depends on pipe class: approximately 345 at 71°C Depends on pipe, grade, schedule, size. Generally 441 for SDR 11 at 49°C 49 Black steel Schedule 40 Thread Black malleable iron 150 177 Black steel Copper, hard Schedule 40 ACR Black malleable iron 150 Wrought or cast Cu 177 93 ABS HDPE Schedule 40 Schedule 40, 80, SDR Flange or weld Solder Flared (soft) Mechanical formed Braze Solvent weld ABS HDPE 93 23 4655 ACR soft 3448 ACR hard 4655 ACR hard 1276 22.4 2021 ASHRAE Handbook—Fundamentals (SI) Table 1 Common Applications of Pipe, Fittings, and Valves for Heating and Air Conditioning (Continued) Application Size, mm 10 to 25 Potable water, 6 to 305 inside building Licensed for single user. © 2021 ASHRAE, Inc. 6 to 305 Material Type PEX SDR-9 Steel, galvanized Copper, hard or soft Copper, hard Joint Type Fitting Material Schedule 40 Thread Type K or L Galv. cast iron 150 Galv. cast iron 150 Wrought or cast Cu Solderc Flared (soft) Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Wrought or cast Cu Solderc Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld CPVC Type M 13 to 203 CPVC Schedule 40,f 80 10 to 25 PEX SDR-9 13 to 152 PE 13 to 152 PP Water serThrough 152 Ductile iron vices, under- 6 to 305 Copper, hard or ground soft 6 to 305 Copper, hard Crimp Clamp Expansion Compression Push fit Proprietary Schedule 40,f 80, Thermal fusion, SDR compression Bronze Brass Copper Engineered plastic Schedule 40,f 80, Thermal fusion, flange, SDR Threade PP Class 50 Type K or L Type M PEX SDR-9 6 to 508 PVC Schedule 40, 80, 120, SDR Copper, hard ABS DWV Solder Schedule DWV, Solvent weld, thread, flange 40,f 80, SDR Schedule 40,f 80, Solvent weld, thread, 120, SDR thermal weld 32 to 508 PV PE aMaximum allowable working pressures have been derated in this table. Higher system pressures can be used for lower temperatures and smaller pipe sizes. Pipe, fittings, joints, and valves must all be considered. bTemperature and pressure relationships can vary based on pipe material composition, size, class, and schedule. cLead- and antimony-based solders are prohibited for potable water systems. Brazing should be used. 38 38 38 862 1034 2551 Type K soft 4378 Type K hard 1724 Type L soft 2999 Type L hard 38 38 2551 Type K soft 1724 Type L soft 2724 Type M hard 38 1586 Type M soft 99 Limit, 93 operating 38 1000 49 (60 limit for Depends on pipe, grade, schedule, some applica- size generally 207 to 758 at 54°C tions) 82 345 Mechanical joint Cast iron Wrought or cast Cu Solderc Flared (soft) Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Flange Bronze Wrought or cast Cu Solderc Rolled groove (51 to 203) Press-connect (13 to 102) Push connect (13 to 51) Mechanical formed Braze Wrought or cast Cu Weld Crimp Bronze Clamp Brass Expansion Copper Compression Engineered plastic Push fit Proprietary PVC Solvent weld, thread,f thermal weld 10 to 25 Drainage, 32 to 203 waste, and 32 to 305 vent (DWV) Systemg Class (When Temperature, Maximum Pressure at Applicable) °C Temperature,a,b kPa 24 38 1724 2551 Type K soft 4378 Type K hard 1724 Type L soft 2999 Type L hard 38 2551 Type K soft 1724 Type L soft 38 38 2724 Type K hard 38 1586 Type M soft 23 1000 66 limit, 60 operating 545 to 724, depending on schedule and size Wrought or cast Cu ABS 38 71 limit PVC 66 limit, 60 operating 1724 DWV hard Depends on pipe class: approximately 345 at 71°C 545 to 724, depending on schedule and size dPiping codes typically require thicker-walled pipe for threaded joints to maintain corrosion allowance and pressure ratings. eAll plumbing codes require both hot and cold water piping to have a 689 kPa at 82°C rating. fThreads are not recommended on Schedule 40 plastic pipe. gDesigner should confirm that all materials are suitably rated for intended opera- tion. Pipe Design 22.5 Table 2 Manufacturers’ Recommendationsa,b for Plastic Materials Cold-water service Hot (60°C) water Potable-water service Drain, waste, and vent (DWV)R Demineralized water Deionized water Salt water Heating (93°C) hot water Natural gas Compressed air Sunlight and weather resistance Underground service Food handling R = Recommended N = Not recommended — = Insufficient information PVC CPVC HDPE PEX PP ABS PVDF RTRP R N R R R R R N N N N R R R R R R R R — — — R N R R R R — R R R — — — R N R R R — — R R R R R R R N N N — R R R R R R R R R N N R R R R R R R — R R — — — — R — R R R R — — R R R — — R R R R R R N N N N R R aBefore selecting material, check availability of suitable range of sizes and fittings and of satisfactory joining method. Also have manufacturer verify the best material for purpose intended. bConsult local building codes for compliance of materials listed. Licensed for single user. © 2021 ASHRAE, Inc. considered; the lowest rating establishes the operating limits of the system. Nonmetallic (Plastic) Pipe Systems Nonmetallic pipe is used in HVAC and plumbing. Plastic is light, generally inexpensive, and corrosion resistant. Plastic also has a low “C” factor (i.e., its surface is very smooth), resulting in lower pumping power requirements and smaller pipe sizes. Plastic pipe’s disadvantages include rapid loss of strength at temperatures above ambient and a high coefficient of linear expansion. The modulus of elasticity of plastics is low, resulting in a short support span. Some jurisdictions do not allow certain plastics in buildings because of toxic products emitted during fires. Plenum-rated plastic and insulation may be used to achieve a plenum rating; check with the authority having jurisdiction (AHJ). Table 2 lists nonmetallic materials used for service water and heating and air-conditioning piping. The pressure and temperature rating of each component selected must be considered; the lowest rating establishes the operating limits of the system. Special Systems Some piping systems are governed by separate codes or standards. Generally, any failure of the piping in these systems is dangerous to the public, so some local areas have adopted laws enforcing the codes, such as the following: • Boiler piping: ASME Standard B31.1 and the ASME Boiler and Pressure Vessel Code (Section I) specify piping inside code-required stop valves on boilers that operate above 100 kPa (gage) with steam, or above 1.1 MPa or 120°C with water. These codes require fabricators and contractors to be certified for such work. The field or shop work must also be inspected while it is in progress, by inspectors commissioned by the National Board of Boiler and Pressure Vessel Inspectors. • Refrigeration piping: ASHRAE Standard 15 and ASME Standard B31.5. • Plumbing systems: Local codes. • Sprinkler systems: NFPA Standard 13. • Fuel gas: NFPA Standard 54/ANSI Standard Z223.1. 1.4 DESIGN EQUATIONS Darcy-Weisbach Equation Pressure drop caused by fluid friction in fully developed flows of all well-behaved (Newtonian) fluids is described by the DarcyWeisbach equation: dominates; at high /D and Re (fully rough limit), the 2/D term L 2 --------- p = f ---- V D 2 (1) where p = pressure drop, Pa f = friction factor, dimensionless (from Moody chart, Figure 13 in Chapter 3) L = length of pipe, m D = internal diameter of pipe, m = fluid density at mean temperature, kg/m3 V = average velocity, m/s This equation is often presented in specific energy form as L V 2 - h = ------p- = f ---- ----g D 2g (2) where h = energy loss, m g = acceleration of gravity, m/s2 In this form, the fluid’s density does not appear explicitly (although it is in the Reynolds number that influences f ). The friction factor f is a function of pipe roughness , inside diameter D, and parameter Re, the Reynolds number: Re = DV/ (3) where Re = Reynolds number, dimensionless = absolute roughness of pipe wall, m = dynamic viscosity of fluid, Pa·s The friction factor is frequently presented on a Moody chart (Figure 13 in Chapter 3) giving f as a function of Re with /D as a parameter. A useful fit of smooth and rough pipe data for the usual turbulent flow regime is the Colebrook equation: 1 - = 1.74 – 2 log 2 18.7 ------- ----- + ------------------ D f Re f (4) Another form of Equation (4) appears in Chapter 21, but the two are equivalent. Equation (4) is useful in showing behavior at limiting cases: as /D approaches 0 (smooth limit), the 18.7/Re f term dominates. 22.6 2021 ASHRAE Handbook—Fundamentals (SI) Table 3 K Factors: Threaded Steel Pipe Fittings Nominal Pipe Dia., mm 90° Ell Reg. 90° Ell Long 45° Ell Return Bend TeeLine TeeBranch Globe Valve Gate Valve Angle Valve Swing Check Valve Bell Mouth Inlet 10 15 20 25 32 40 50 65 80 100 2.5 2.1 1.7 1.5 1.3 1.2 1.0 0.85 0.80 0.70 — — 0.92 0.78 0.65 0.54 0.42 0.35 0.31 0.24 0.38 0.37 0.35 0.34 0.33 0.32 0.31 0.30 0.29 0.28 2.5 2.1 1.7 1.5 1.3 1.2 1.0 0.85 0.80 0.70 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 2.7 2.4 2.1 1.8 1.7 1.6 1.4 1.3 1.2 1.1 20 14 10 9 8.5 8 7 6.5 6 5.7 0.40 0.33 0.28 0.24 0.22 0.19 0.17 0.16 0.14 0.12 — — 6.1 4.6 3.6 2.9 2.1 1.6 1.3 1.0 8.0 5.5 3.7 3.0 2.7 2.5 2.3 2.2 2.1 2.0 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Square Projected Inlet Inlet 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Source: Engineering Data Book (Hydraulic Institute 1990). Licensed for single user. © 2021 ASHRAE, Inc. Table 4 K Factors: Flanged Welded Steel Pipe Fittings Nominal Pipe Dia., mm 90° Ell Reg. 90° Ell Long 45° Ell Long 25 32 40 50 65 80 100 150 200 250 300 0.43 0.41 0.40 0.38 0.35 0.34 0.31 0.29 0.27 0.25 0.24 0.41 0.37 0.35 0.30 0.28 0.25 0.22 0.18 0.16 0.14 0.13 0.22 0.22 0.21 0.20 0.19 0.18 0.18 0.17 0.17 0.16 0.16 Return Return Bend Bend LongStandard Radius 0.43 0.41 0.40 0.38 0.35 0.34 0.31 0.29 0.27 0.25 0.24 0.43 0.38 0.35 0.30 0.27 0.25 0.22 0.18 0.15 0.14 0.13 TeeLine TeeBranch Globe Valve Gate Valve Angle Valve Swing Check Valve 0.26 0.25 0.23 0.20 0.18 0.17 0.15 0.12 0.10 0.09 0.08 1.0 0.95 0.90 0.84 0.79 0.76 0.70 0.62 0.58 0.53 0.50 13 12 10 9 8 7 6.5 6 5.7 5.7 5.7 — — — 0.34 0.27 0.22 0.16 0.10 0.08 0.06 0.05 4.8 3.7 3.0 2.5 2.3 2.2 2.1 2.1 2.1 2.1 2.1 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Source: Engineering Data Book (Hydraulic Institute 1990). Equation (4) is implicit in f; that is, f appears on both sides, so a value for f is usually obtained iteratively. Solution: Use Equation (7). From Table 3, the K for a 25 mm, 90° threaded elbow is 1.5. Hazen-Williams Equation A less widely used alternative to the Darcy-Weisbach formulation for calculating pressure drop is the Hazen-Williams equation, which is expressed as V p = 6.819L ---- C Example 1. Determine the pressure drop for 15°C water flowing at 1 m/s through a nominal 25 mm, 90° threaded elbow. 1.852 1.167 1 ---- D (g) (5) or p = 1.5 1000 12/2 = 750 Pa The loss coefficient for valves appears in another form as Av , a dimensional coefficient expressing the flow through a valve at a specified pressure drop. Q = A v p (8) where V h = 6.819L ---- C 1.852 1 ---- D 1.167 (6) where C = roughness factor. Typical values of C are 150 for plastic pipe and copper tubing, 140 for new steel pipe, down to 100 and below for badly corroded or very rough pipe. Valve and Fitting Losses Valves and fittings cause pressure losses greater than those caused by the pipe alone. One formulation expresses losses as V 2 V 2 p = K ----- or h = K ----- 2 2g (7) where K = geometry- and size-dependent loss coefficient (Tables 3 to 6)and = density of fluid 1000 kg/m3 for water at temperatures below 120°C. Q = volumetric flow, m3/s Av = valve coefficient, m3/s at p = 1 Pa p = pressure drop, Pa See the section on Control Valve Sizing in Chapter 46 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment for more information on valve coefficients. Example 2. Determine the volumetric flow through a valve with Av = 0.00024 for an allowable pressure drop of 35 kPa. Solution: Use Equation (8). Q = 0.00024 35 000 1000 = 0.0014 m3/s = 1.4 L/s Alternative formulations express fitting losses in terms of equivalent lengths of straight pipe (see Tables 8 and 27). Pressure loss data for fittings are also presented in Idelchik (1986). Equation (7) and data in Tables 3 and 4 are based on the assumption that separated flow in the fitting causes the K factors to be independent of Reynolds number. In reality, the K factor for most pipe fittings Pipe Design 22.7 Table 5 Approximate Range of Variation for K Factors of Steel Fittings 90° Elbow Regular threaded ±20% above 50 mm Tee ±40% below 50 mm Long-radius threaded 45° Elbow Return bend (180°) ±25% Regular flanged ±35% Long-radius flanged ±30% Regular threaded ±10% Long-radius flanged ±10% Regular threaded ±25% Regular flanged ±35% Long-radius flanged ±30% Threaded, line or branch ±25% Flanged, line or branch ±35% Globe valve Threaded ±25% Flanged ±25% Gate valve Threaded ±25% Flanged ±50% Angle valve Threaded ±20% Flanged ±50% Check valve Threaded ±50% Flanged +200% –80% Source: Engineering Data Book (Hydraulic Institute 1990). Table 6 Summary of K Values for Steel Ells, Reducers, and Expansions Licensed for single user. © 2021 ASHRAE, Inc. ASHRAE Researchb,c Past a 1.2 m/s 2.4 m/s 3.6 m/s 50 mm S.R.e ell (R/D = 1) thread 0.60 to 1.0 (1.0)d 100 mm S.R. ell (R/D = 1) weld 0.30 to 0.34 0.60 0.37 0.68 0.34 0.736 0.33 25 mm L.R. ell (R/D = 1.5) weld 50 mm L.R. ell (R/D = 1.5) weld 100 mm L.R. ell (R/D = 1.5) weld 150 mm L.R. ell (R/D = 1.5) weld 200 mm L.R. ell (R/D = 1.5) weld 250 mm L.R. ell (R/D = 1.5) weld 300 mm L.R. ell (R/D = 1.5) weld 400 mm L.R. ell (R/D = 1.5) weld 500 mm L.R. ell (R/D = 1.5) weld 600 mm L.R. ell (R/D = 1.5) weld Reducer (50 by 40 mm) thread (100 by 80 mm) weld (150 by 100 mm) weld (200 by 150 mm) weld (250 by 200 mm) weld (300 by 250 mm) weld (400 by 300 mm) weld (500 by 400 mm) weld (600 by 500 mm) weld Expansion (40 by 50 mm) thread (80 by 100 mm) weld (100 by 150 mm) weld (150 by 200 mm) weld (200 by 250 mm) weld (250 by 300 mm) weld (300 by 400 mm) weld (400 by 500 mm) weld (500 by 600 mm) weld to 1.0 0.50 to 0.7 0.22 to 0.33 (0.22)d 0.25 0.20 to 0.26 0.17 0.16 0.12 0.09 0.07 — 0.22 — — 0.26 0.26 0.22 0.21 0.17 0.12 0.12 0.098 0.53 0.23 0.62 0.31 0.16 0.14 0.17 0.16 0.053 0.16 0.11 0.28 0.15 0.11 0.11 0.073 0.024 0.020 — — 0.24 0.24 0.20 0.17 0.17 0.12 0.10 0.089 0.28 0.14 0.54 0.28 0.14 0.14 0.16 0.13 0.053 0.13 0.11 0.28 0.12 0.09 0.11 0.076 0.021 0.023 — — 0.23 0.24 0.19 0.16 0.17 0.11 0.10 0.089 0.20 0.10 0.53 0.26 0.14 0.14 0.17 0.13 0.055 0.02 0.11 0.29 0.11 0.08 0.11 0.073 0.022 0.020 Source: Rahmeyer (2003a). aPublished data by Crane Co. (1988), Freeman (1941), and Hydraulic Institute (1990). bRahmeyer (1999a, 2002a). varies with Reynolds number. Tests by Rahmeyer (1999a, 1999b, 2002a, 2002b) (ASHRAE research projects RP-968 and RP-1034) on 50 mm threaded and 100, 300, 400, 500, and 600 mm welded steel fittings demonstrate the variation and are shown in Tables 6 and 7. The studies also present K factors of diverting and mixing flows in tees, ranging from full through flow to full branch flow. They also examined the variation in K factors caused by variations in geometry among manufacturers and by surface defects in individual fittings. Hegberg (1995) and Rahmeyer (1999a, 1999b) discuss the origins of some of the data shown in Tables 6 and 7. The Hydraulic Institute (1990) data appear to have come from Freeman (1941), — — — — — — — — — — — — — cDing et al. (2005) d ( ) Data published in 1993 ASHRAE Handbook—Fundamentals. eS.R.—short radius or regular ell; L.R.—long-radius ell. work that was actually performed in 1895. The work of Giesecke (1926) and Giesecke and Badgett (1931, 1932a, 1932b) may not be representative of present-day fittings. Further extending the work on determination of fitting K factors to PVC piping systems, Rahmeyer (2003a, 2003b) (ASHRAE research project RP-1193) found the data in Tables 8 and 9 giving K factors for Schedule 80 PVC 50, 100, 150, and 200 mm ells, reducers, expansions, and tees. The results of these tests are also presented in the cited papers in terms of equivalent lengths. In general, PVC fitting geometry varied much more from one manufacturer to another than steel fittings did. 22.8 2021 ASHRAE Handbook—Fundamentals (SI) Table 7 Summary of Test Data for Loss Coefficients K for Steel Pipe Tees Licensed for single user. © 2021 ASHRAE, Inc. ASHRAE Researchb,c Pasta 1.2 m/s 2.4 m/s 3.6 m/s 50 mm thread tee, 100% branch 100% line (flow-through) 100% mix 1.20 to 1.80 (1.4)d 0.50 to 0.90 (0.90)d — 0.93 0.19 1.19 — — — — — 100 mm weld tee, 100% branch 100% line (flow-through) 100% mix 0.70 to 1.02 (0.70)d 0.15 to 0.34 (0.15)d — — — — 0.57 0.06 0.49 — — — 150 mm weld tee, 100% branch 100% line (flow-through) 100% mix — — — — — — 0.56 0.12 0.88 — — — 200 mm weld tee, 100% branch 100% line (flow-through) 100% mix — — — — — — 0.53 0.08 0.70 — — — 250 mm weld tee, 100% branch 100% line (flow-through) 100% mix — — — — — — 0.52 0.06 0.77 — — — 300 mm weld tee, 100% branch 100% line (flow-through) 100% mix 0.52 0.09 — 0.70 0.062 0.88 0.63 0.091 0.72 0.62 0.096 0.72 400 mm weld tee, 100% branch 100% line (flow-through) 100% mix 0.47 0.07 — 0.54 0.032 0.74 0.55 0.028 0.74 0.54 0.028 0.76 aPublished data by Crane Co. (1988), Freeman (1941), and Hydraulic Institute (1990). cDing et al. (2005). bRahmeyer (1999b, 2002b). dData published in 1993 ASHRAE Handbook—Fundamentals. Table 8 Test Summary for Loss Coefficients K and Equivalent Loss Lengths Schedule 80 PVC Fitting Injected molded elbow, 50 mm 100 mm 150 mm 200 mm K L, m 0.91 to 1.00 0.86 to 0.91 0.76 to 0.91 0.68 to 0.87 2.6 to 2.8 5.6 to 5.9 8.0 to 9.5 10.0 to 12.8 200 mm fabricated elbow, Type I, components Type II, mitered 0.40 to 0.42 5.9 to 6.2 0.073 to 0.76 10.8 to 11.2 150 by 100 mm injected molded reducer Bushing type 0.12 to 0.59 0.49 to 0.59 1.2 to 6.2 5.2 to 6.2 200 by 150 mm injected molded reducer Bushing type Gradual reducer type 0.13 to 0.63 0.48 to 0.68 0.21 1.9 to 9.3 7.1 to 10.0 3.1 100 by 150 mm injected molded expansion 0.069 to 1.19 Bushing type 0.069 to 1.14 0.46 to 7.7 0.46 to 7.4 150 by 200 mm injected molded expansion 0.95 to 0.96 Bushing type 0.94 to 0.95 Gradual reducer type 0.99 10.0 to 10.1 9.9 to 10.0 10.4 Losses in Multiple Fittings Typical fitting loss calculations are done as if each fitting is isolated and has no interaction with any other. Rahmeyer (2002c) (ASHRAE research project RP-1035) tested 50 mm threaded ells and 100 mm ells in two and three fitting assemblies of several geometries, at varying spacing. Figure 1 shows the geometries, and Figures 2 and 3 show the ratio of coupled K values to uncoupled K values (i.e., fitting losses for the assembly compared with the sum of losses from the same number of isolated fittings). The most important conclusion is that the interaction between fittings always reduces the loss. Also, although geometry of the assembly has a definite effect, the effects are not the same for 50 mm threaded and 100 mm welded ells. Thus, the traditional Fig. 1 Close-Coupled Test Configurations practice of adding together losses from individual fittings gives a conservative (high-limit) estimate. Calculating Pressure Losses The most common engineering design flow loss calculation selects a pipe size for the desired total flow rate and available or allowable pressure drop. Because either formulation of fitting losses requires a known diameter, pipe size must be selected before calculating the detailed influence of fittings. A frequently used rule of thumb assumes that the design length of pipe is 50 to 100% longer than actual to account for fitting losses. After a pipe diameter has been selected on this basis, the influence of each fitting can be evaluated. Stress Calculations Metallic Pipe. Although stress calculations are seldom required, the factors involved should be understood. The main areas of concern are (1) internal pressure stress, (2) longitudinal stress caused by pressure and mass, and (3) stress from expansion and contraction. ASME Standard B31 standards establish a basic allowable stress S equal to one-fourth of the minimum tensile strength of the material. This value is adjusted, as discussed in this section, because of the nature of certain stresses and manufacturing processes. Pipe Design 22.9 Table 9 Test Summary for Loss Coefficients K of PVC Tees Branching K1-2 Schedule 80 PVC Fitting Fig. 2 Summary Plot of Effect of Close-Coupled Configurations for 50 mm Ells Licensed for single user. © 2021 ASHRAE, Inc. K1-3 50 mm injection molded branching tee, 100% 0.13 to 0.26 — line flow 50/50 flow 0 to 0.12 0.74 to 1.02 100% branch flow — 0.98 to 1.39 100 mm injection molded branching tee, 100% 0.07 to 0.22 — line flow 50/50 flow 0.03 to 0.13 0.74 to 0.82 100% branch flow — 0.97 to 1.12 150 mm injection molded branching tee, 100% 0.01 to 0.14 — line flow 50/50 flow 0.06 to 0.11 0.70 to 0.84 100% branch flow — 0.95 to 1.15 150 mm fabricated branching tee, 100% line flow 0.21 to 0.22 — 50/50 flow 0.04 to 0.09 1.29 to 1.40 100% branch flow — 1.74 to 1.88 200 mm injection molded branching tee, 100% 0.04 to 0.09 — line flow 50/50 flow 0.04 to 0.07 0.64 to 0.75 100% branch flow — 0.85 to 0.96 200 mm fabricated branching tee, 100% line flow 0.09 to 0.16 — 50/50 flow 0.08 to 0.13 1.07 to 1.16 100% branch flow — 1.40 to 1.62 Mixing PVC Fitting Fig. 3 Summary Plot of Effect of Close-Coupled Configurations for 100 mm Ells Hoop stress caused by internal pressure is the major stress on pipes. Because some forming methods form a seam that may be weaker than the base material, ASME Standard B31.9 specifies a joint efficiency factor E, multiplied by the basic allowable stress to establish a maximum allowable stress value in tension SE. (Table A-1 in ASME Standard B31.9 lists values of SE for commonly used pipe materials.) The joint efficiency factor can be significant; for example, seamless pipe has a joint efficiency factor of 1, so it can be used to the full allowable stress (one-quarter of the tensile strength). In contrast, butt-welded pipe has a joint efficiency factor of 0.60, so its maximum allowable stress must be derated (SE = 0.6S). Equation (9) determines the minimum wall thickness for a given pressure. Equation (10) determines the maximum pressure allowed for a given wall thickness. pD t m = --------- + A 2S E (9) 2S E t m – A p = ----------------------------D (10) K1-2 K3-2 50 mm injection molded mixing tee, 100% line 0.12 to 0.25 — flow 50/50 flow 1.22 to 1.19 0.89 to 1.88 100% mix flow — 0.89 to 1.54 100 mm injection molded mixing tee, 100% line 0.07 to 0.18 — flow 50/50 flow 1.19 to 1.88 0.98 to 1.88 100% mix flow — 0.88 to 1.02 150 mm injection molded mixing tee, 100% line 0.06 to 0.14 — flow 50/50 flow 1.26 to 1.80 1.02 to 1.60 100% mix flow — 0.90 to 1.07 150 mm fabricated mixing tee, 100% line flow 0.19 to 0.21 — 50/50 flow 2.94 to 3.32 2.57 to 3.17 100% mix flow — 1.72 to 1.98 200 mm injection molded mixing tee, 100% line 0.04 to 0.09 — flow 50/50 flow 1.10 to 1.60 0.96 to 1.32 100% mix flow — 0.81 to 0.93 200 mm fabricated mixing tee, 100% line flow 0.13 to 0.70 — 50/50 flow 2.36 to 10.62 2.02 to 2.67 100% mix flow — 1.34 to 1.53 Coefficients based on average velocity of 2.43 m/s. Range of values varies with fitting manufacturers. Line or straight flow is Q2/Q1 = 100%. Branch flow is Q2/Q1 = 0%. where SA = allowable stress range, kPa Sc = allowable cold stress at coolest temperature system will experience, kPa Sh = allowable hot stress at hottest temperature system will experience, kPa Both equations incorporate an allowance factor A to compensate for manufacturing tolerances, material removed in threading or grooving, and corrosion. For the seamless, butt-welded, and electric resistance welded (ERW) pipe most commonly used in HVAC work, the standards apply a manufacturing tolerance of 12.5%. Working pressure for steel pipe (see Table 16) has been calculated using a manufacturing tolerance of 12.5%, standard allowance for depth of thread (where applicable), and a corrosion allowance of 1.65 mm for pipes 65 mm and larger and 0.64 mm for pipes 50 mm 22.10 2021 ASHRAE Handbook—Fundamentals (SI) and smaller. Where corrosion is known to be greater or smaller, pressure rating can be recalculated using Equation (10). Higher pressure ratings than shown in Table 16 can be obtained (1) by using ERW or seamless pipe in lieu of continuous-weld (CW) pipe 100 mm and less, and seamless pipe in lieu of ERW pipe 125 mm and greater (because of higher joint efficiency factors); or (2) by using heavier-wall pipe. Longitudinal stresses caused by pressure, mass, and other sustained forces are additive, and the sum of all such stresses must not exceed the basic allowable stress S at the highest temperature at which the system will operate. Longitudinal stress caused by pressure equals approximately one-half the hoop stress caused by internal pressure; thus, at least one-half the basic allowable stress is available for mass and other sustained forces. This factor is taken into account in Table 11. Stresses caused by expansion and contraction are cyclical, and, because creep allows some stress relaxation, the ASME Standard B31 series allows designing to an allowable stress range SA as calculated by Equation (11). Table 15 lists allowable stress ranges for commonly used piping materials. SA = 1.25Sc + 0.25Sh (11) Licensed for single user. © 2021 ASHRAE, Inc. where SA = allowable stress range, kPa Sc = allowable cold stress at coolest temperature system will experience, kPa Sh = allowable hot stress at hottest temperature system will experience, kPa Nonmetallic. Both thermoplastics and thermosets have an allowable stress derived from a hydrostatic design basis stress (HDBS). The HDBS is determined by a statistical analysis of both static and cyclic stress rupture test data as set forth in ASTM Standard D2837 for thermoplastics and ASTM Standard D2992 for glass-fiber-reinforced thermosetting resins. The allowable stress, called the hydrostatic design stress (HDS), is obtained by multiplying the HDBS by a service factor. HDS values recommended by some manufacturers and those allowed by ASME Standard B31 are listed in Table 18. The pressure design thickness for plastic pipe can be calculated using the code stress values and the formula in Equation (12): t = pD/(2S + p) There are many formulations of the polymers used for piping materials, and different joining methods for each, so manufacturers’ recommendations should be followed. Most catalogs give pressure ratings for pipe and fittings at various temperatures up to the maximum the material will withstand. 1.5 A procedure for sizing piping systems is as follows: 1. Determine system type (open, closed, compressible, incompressible, pumped, gravity feed, domestic, etc.). 2. Determine type and properties of fluid to be conveyed in the pipe. 3. Determine temperatures used (high, low) and temperature differentials. 4. Identify system pressures encountered in the system (working, maximum, low, fill, and relief pressures). 5. Determine load at each device (e.g., heating or cooling requirements, fixture units for plumbing) to find flow. 6. Sketch main, risers, and branches, and indicate equipment to be served and each device’s flow rate. 7. Determine flow of supply pipe for each pipe segment run by summing the loads at the furthest device and running back to the source. 8. Determine flow of each return pipe by starting at the first device returning water and summing the loads back to the source (when applicable). 9. Determine equivalent length of pipe in the main lines, risers, branches, and returns. Because pipe sizes are not known, the exact equivalent length of various fittings cannot be determined. Add the equivalent lengths, starting at the beginning and proceeding along the mains, risers, branches, and returns (when applicable). 10. In domestic or gravity feed: calculate the approximate design value of the average pressure drop per metre length of pipe in equivalent length determined in step 9. In pumped system: calculate pressure drop H using the flow rate and pressure drop for pipe from Equations (2) or (6), the valves and fittings using head drop from Equation (7), and head from the devices from the manufacturer’s data. p = (ps – 9.8H – pf – pm)/L (12) where SIZING PROCEDURE (14) where t = pressure design thickness, mm p = internal design pressure, kPa (gage) D = pipe outside diameter, mm S = hydrostatic design stress (HDS), kPa The minimum required wall thickness can be found by adding an allowance for mechanical strength, threading, grooving, erosion, and corrosion to the calculated pressure design thickness. Another method of rating pressure rating of piping used by manufacturers is the standard dimension ratio (SDR), which is the ratio of the pipe diameter to the wall thickness: SDR= D/s (13) where D = pipe outside diameter, mm s = pipe wall thickness, mm An SDR of 11 means that the outside diameter D of the pipe is 11 times the thickness of the wall s. A high SDR means that the pipe’s wall is thin compared to its diameter, and a low SDR means that the pipe’s wall is thick relative to pipe diameter. SDR is inversely correlated with pressure rating: high SDR indicates a low pressure rating, whereas low-SDR pipes have higher pressure ratings. p = average pressure loss per metre of equivalent length of pipe, kPa ps = pressure at the source, kPa pf = minimum pressure required to operate device, kPa pm = pressure drop through any meters, kPa H = height of highest fixture above source (if open system), m L = equivalent length determined in step 4, m 11. In domestic or gravity system: from the expected rate of flow (step 5) and p (step 10), select pipe sizes. In pumped system: select the pump using the flow rate and calculated H. 1.6 PIPE-SUPPORTING ELEMENTS Pipe-supporting elements consist of (1) hangers, which support from above; (2) supports, which bear load from below; and (3) restraints, such as anchors and guides, that limit or direct movement as well as support loads. Pipe-supporting elements must withstand all static and dynamic conditions, including the following: • Mass of pipe, valves, fittings, insulation, and fluid contents, including test fluid if using heavier-than-normal media • Occasional loads such as ice, wind, and seismic forces or testing loads (e.g., hydrostatic loads on a steam pipe) Pipe Design 22.11 Table 10 Capacities of ASTM A36 Steel Threaded Rods Rod Diameter, mm Root Area of Coarse Thread, mm2 Maximum Load,* N 6.4 10 13 16 19 22 25 32 17.4 43.9 81.3 130.3 194.8 270.3 356.1 573.5 1 070 2 720 5 030 8 060 12 100 16 800 22 100 35 600 *Based on allowable stress of 83 MPa reduced by 25% using root area in accordance with ASME Standard B31.1 and MSS Standard SP-58. Licensed for single user. © 2021 ASHRAE, Inc. • Forces imposed by thermal expansion and contraction of pipe bends and loops • Frictional, spring, and pressure thrust forces imposed by expansion joints in the system • Frictional forces of guides and supports • Other loads (e.g., water hammer, vibration, reactive force of relief valves) • Test load and force In addition, pipe-supporting elements must be evaluated in terms of stress at the points of connection to the pipe and the building. Stress at the point of connection to the pipe is especially important for base elbow and trunnion supports, because this stress is usually the limiting parameter, not the strength of the structural member. Loads on anchors, cast-in-place inserts, and other attachments to concrete should not be more than one-fifth the ultimate strength of the attachment, as determined by manufacturers’ tests. All loads on the structure should be communicated to and coordinated with the structural engineer. The ASME B31 standards establish criteria for the design of pipe-supporting elements, and the Manufacturers Standardization Society of the Valve and Fittings Industry (MSS) has established standards for the design, fabrication, selection, and installation of pipe hangers and supports based on these codes. MSS Standard SP-69 and the catalogs of many manufacturers illustrate the various hangers and components and provide information on the types to use with different pipe systems. Table 10 lists maximum safe loads for threaded steel rods, and Tables 11 and 12 show suggested pipe support spacing for metal and PVC pipes, respectively. Loads on most pipe-supporting elements are moderate and can be selected safely in accordance with manufacturers’ catalog data and the information presented in this section; however, some loads and forces can be very high, especially in multistory buildings and for large-diameter pipe, particularly where expansion joints are used at a high operating pressure. Consequently, a qualified engineer should design or review all anchors and pipe-supporting elements, especially for the following: • Steam systems operating above 100 kPa (gage) • Hydronic systems operating above 1.1 MPa or 120°C • Risers over 10 stories or 30 m • Systems with expansion joints, especially for pipe diameters 80 mm and greater • Pipe sizes over 300 mm diameter • Anchor loads greater than 44 kN • Moments on pipe or structure in excess of 1.4 kN·m Table 11 Suggested Hanger Spacing and Rod Size for Straight Horizontal Runs Nominal O.D., mm 15 20 25 40 50 65 80 100 150 200 250 300 350 400 450 500 Hanger Spacing, m Standard Steel Pipe* Copper Tube Water Steam Water 2.1 2.1 2.1 2.7 3.0 3.4 3.7 4.3 5.2 5.8 6.1 7.0 7.6 8.2 8.5 9.1 2.4 2.7 2.7 3.7 4.0 4.3 4.6 5.2 6.4 7.3 7.9 9.1 9.8 10.7 11.3 11.9 1.5 1.5 1.8 2.4 2.4 2.7 3.0 3.7 4.3 4.9 5.5 5.8 Rod Size, mm 6.4 6.4 6.4 10 10 10 10 13 13 16 19 22 25 25 32 32 Source: Adapted from MSS Standard SP-69 *Spacing does not apply where span calculations are made or where concentrated loads are placed between supports such as flanges, valves, specialties, etc. are hoop stress caused by internal pressure, and longitudinal stresses caused by pressure, mass, and other sustained loads. Detailed stress calculations are seldom required for HVAC applications because standard pipe has ample thickness to sustain the pressure and longitudinal stress caused by mass (assuming hangers are spaced in accordance with Table 11). Support spacings for PVC and CPVC pipe systems are influenced by operating temperatures. Table 12 recommends horizontal spacing based on pipe size, schedule, material (PVC or industrialgrade CPVC), and operating temperature. Hangers and supports should not be clamped tightly because the axial movement of the pipe would be restricted. The charts are based on continuous spans and uninsulated lines carrying liquids. They are not applicable where loads between supports are concentrated (e.g., for valves, flanges) or where there is a change in direction. Hangers/supports should be located adjacent to joints, branch connections, and changes in direction. Risers should be in installed independently of adjacent horizontal hangers/supports. For cast iron pipe, maximum spacing should be 3.7 m, with at least one hanger/support for each pipe section. 1.7 PIPE EXPANSION AND FLEXIBILITY Temperature changes cause dimensional changes in all materials. Table 13 shows the coefficients of expansion for metallic piping materials commonly used in HVAC. For systems operating at high temperatures, such as steam and hot water, the rate of expansion is high, and significant movements can occur in short runs of piping. Even though rates of expansion may be low for systems operating in the range of 5 to 40°C, such as chilled and condenser water, they can cause large movements in long runs of piping, which are common in distribution systems and high-rise buildings. Therefore, in addition to design requirements for pressure, mass, and other loads, piping systems must accommodate thermal and other movements to prevent the following: Hanger Spacing and Pipe Wall Thickness • Failure of pipe and supports from overstress and fatigue • Leakage of joints • Detrimental forces and stresses in connected equipment Table 11 suggests minimum pipe hanger spacing for use unless exceeded by the local authority having jurisdiction or engineering calculations. The primary factors determining pipe wall thickness An unrestrained pipe operates at the lowest overall stress level. Anchors and restraints are needed to support pipe mass and to protect equipment connections. Anchor forces and bowing of pipe 22.12 2021 ASHRAE Handbook—Fundamentals (SI) Licensed for single user. © 2021 ASHRAE, Inc. Table 12 Suggested Maximum Spacing Between Hangers/Support for PVC and CPVC Pipe anchored at both ends are generally too large to be acceptable, so general practice is to never anchor a straight run of steel pipe at both ends. Piping must be allowed to expand or contract through thermal changes. Ample flexibility can be attained by designing pipe bends and loops or by including supplemental devices, such as expansion joints. End reactions transmitted to rotating equipment, such as pumps or turbines, may deform the equipment case and cause bearing misalignment that may ultimately cause the component to fail. Consequently, manufacturers’ recommendations on allowable forces and movements that may be placed on their equipment should be followed. 1.8 Fig. 4 Guided Cantilever Beam PIPE BENDS AND LOOPS Detailed stress analysis requires involved mathematical analysis and is generally performed by computer programs. However, such involved analysis is not typically required for most HVAC systems because the piping arrangements and temperature ranges at which they operate are usually simple to analyze. Expansion stresses discussed in this section relate only to aboveground pipe located in open air, or preinsulated pipe. L Bends The guided cantilever beam method of evaluating L bends can be used to design L bends, Z bends, pipe loops, branch take-off connections, and some more complicated piping configurations. The guided cantilever equation [see Equation (17)] is generally conservative because it assumes that the pipe arrangement does not rotate. The anchor force results will be higher because of the lack of rotation, and rigorous analysis is recommended for complicated or expensive systems. Equation (15) may be used to calculate the length of leg BC needed to accommodate thermal expansion or contraction of leg AB for a guided cantilever beam (Figure 4). L= 3 DE-------------SA (15) where L = length of leg BC required to accommodate thermal expansion of long leg AB, mm = thermal expansion or contraction of leg AB, mm D = actual pipe outside diameter, mm E = modulus of elasticity, kPa SA = allowable stress range, kPa For the commonly used A53 Grade B seamless or ERW pipe, an allowable stress SA of 155 MPa (see Table 15) can be used without overstressing the pipe. However, this can result in very high end reactions and anchor forces, especially with large-diameter pipe. Designing to a stress range SA of 103 MPa and assuming E = 193 GPa, Equation (15) reduces to Equation (16), which provides reasonably low end reactions without requiring too much extra pipe. In addition, Equation (16) may be used with A53 continuous (butt-) welded, seamless, and ERW pipe, and B88 drawn copper tubing. L = 75 D (16) Pipe Design Table 13 22.13 Thermal Expansion of Metal Pipe Licensed for single user. © 2021 ASHRAE, Inc. Vacuum Linear Thermal Expansion, mm/m Saturated Steam Pressure, Temperature, Carbon Type 304 kPa (gage) °C Steel Stainless Steel Copper –34 –29 –23 –18 –12 –7 –0.16 –0.10 –0.05 0.00 0.07 0.13 –0.25 –0.17 –0.08 0.00 0.09 0.18 –0.27 –0.18 –0.09 0.00 0.10 0.20 –100.7 –100.7 –100.0 –99.3 –98.6 –97.9 –96.5 –94.5 –89.6 –81.4 –69.0 –49.6 –22.1 0 4 10 16 21 27 32 38 49 60 71 82 93 0.20 0.25 0.32 0.38 0.44 0.51 0.57 0.63 0.76 0.88 1.02 1.14 1.27 0.30 0.38 0.47 0.56 0.65 0.75 0.84 0.93 1.13 1.31 1.49 1.68 1.87 0.31 0.38 0.47 0.57 0.66 0.75 0.85 0.94 1.14 1.33 1.50 1.71 1.92 0 17.2 71.0 142.7 238.6 360.6 517.1 712.3 953.6 1249 100 104 116 127 138 149 160 171 182 193 1.35 1.41 1.54 1.68 1.82 1.96 2.11 2.25 2.40 2.54 1.98 2.07 2.26 2.45 2.64 2.83 3.03 3.23 3.43 3.63 2.03 2.10 2.30 2.49 2.68 2.88 3.08 3.28 3.48 3.68 1604 9039 204 304 404 504 2.69 4.11 5.67 7.31 3.83 5.65 7.56 9.54 4.06 5.77 7.72 9.76 The guided cantilever method of designing L bends assumes no restraints; therefore, care must be taken in supporting the pipe. For horizontal L bends, it is usually necessary to place a support near point B (see Figure 4), and any supports between points A and C must provide minimal resistance to piping movement; this is done by using slide plates or hanger rods of ample length, with hanger components selected to allow for swing no greater than 4°. For L bends containing both vertical and horizontal legs, any supports on the horizontal leg must be spring hangers designed to support the full mass of pipe at normal operating temperature with a maximum load variation of 25%. The force developed in an L bend that must be sustained by anchors or connected equipment is determined by the following equation: 12E c I F = ----------------6 10 L 3 where F = force, kN Ec = modulus of elasticity, kPa I = moment of inertia, mm4 L = length of offset leg, mm = deflection of offset leg, mm (17) Fig. 5 Z Bend in Pipe Z Bends Z bends, as shown in Figure 5, are very effective for accommodating pipe movements. A simple and conservative method of sizing Z bends is to design the offset leg to be 65% of the values used for an L bend in Equation (15): L = 48.7 D (18) where L = length of offset leg, mm = anchor-to-anchor expansion, mm D = pipe outside diameter, mm The force developed in a Z bend can be calculated with acceptable accuracy as follows: F = C1(D/L)2 (19) where C1 = 101 kN/mm F = force, kN D = pipe outside diameter, mm L = length of offset leg, mm = anchor-to-anchor expansion, mm U Bends and Pipe Loops Pipe loops or U bends are commonly used in long runs of piping. A simple method of designing pipe loops is to calculate the anchorto-anchor expansion and, using Equation (15), determine the length L necessary to accommodate this movement. The pipe loop dimensions can then be determined using W = L/5 and H = 2W. Note that guides must be spaced no closer than twice the height of the loop, and piping between guides must be supported, as described in the section on L Bends, when the length of pipe between guides exceeds the maximum allowable hanger spacing for the size pipe. Table 14 lists pipe loop dimensions for pipe sizes 25 to 600 mm and anchor-to-anchor expansion (contraction) of 50 to 300 mm. No simple method has been developed to calculate pipe loop force; however, it is generally low. A conservative estimate is 35 N per millimetre diameter (e.g., a 50 mm pipe will develop 1.75 kN of force and a 300 mm pipe will develop 10.5 kN of force). Additional analysis should be done for pipes greater than 300 mm in diameter, because other simplified methodologies predict higher anchor forces. Expansion and Contraction Control of Other Materials To design expansion and contraction loops and bends for other materials, consult the Copper Development Association (CDA 2010) for copper pipes, and Plastic Pipe and Fitting Association (PPFA 2009) for plastic pipes. 22.14 2021 ASHRAE Handbook—Fundamentals (SI) Licensed for single user. © 2021 ASHRAE, Inc. Table 14 Pipe Loop Design for A53 Grade B Carbon Steel Pipe Through 200°C Pipe Nom., O.D., mm Anchor-to-Anchor Expansion, mm W H W H W H W H W H W H 25 50 80 100 150 200 250 300 350 400 450 500 600 0.6 0.9 1.1 1.2 1.5 1.7 1.8 2.0 2.1 2.3 2.4 2.6 2.7 1.2 1.8 2.1 2.4 3.0 3.4 3.7 4.0 4.3 4.6 4.9 5.2 5.5 0.9 1.2 1.5 1.7 2.0 2.3 2.6 2.7 2.9 3.0 3.4 3.5 3.8 1.8 2.4 3.0 3.4 4.0 4.6 5.2 5.5 5.8 6.1 6.7 7.0 7.6 1.1 1.5 1.8 2.0 2.4 2.7 3.0 3.4 3.5 3.8 4.0 4.3 4.4 2.1 3.0 3.7 4.0 4.9 5.5 6.1 6.7 7.0 7.6 7.9 8.5 8.8 1.2 1.7 2.0 2.3 2.7 3.2 3.5 3.8 4.0 4.3 4.6 4.9 5.3 2.4 3.4 4.0 4.6 5.5 6.4 7.0 7.6 7.9 8.5 9.1 9.8 10.7 1.4 1.8 2.3 2.6 3.0 3.7 4.0 4.3 4.6 4.9 5.2 5.5 5.9 2.7 3.7 4.6 5.2 6.1 7.3 7.9 8.5 9.1 9.8 10.4 11.0 11.9 1.5 2.1 2.4 2.7 3.4 4.0 4.3 4.7 4.9 5.3 5.6 5.9 6.4 3.0 4.3 4.9 5.5 6.7 7.9 8.5 9.4 9.8 10.7 11.3 11.9 12.8 Notes: 1. W and H dimensions are metres. 2. L is determined from Equation (15). W = L/5 H = 2W 2H + W = L 50 100 150 200 250 300 3. Approximate force to deflect loop = 35 N/mm pipe diameter. For example, 200 mm pipe creates 7600 N of force. Cold Springing of Pipe Cold springing or cold positioning of pipe consists of offsetting or springing the pipe in a direction opposite the expected movement. Cold springing is not recommended for most HVAC piping. Furthermore, cold springing does not allow designing a pipe bend or loop for twice the calculated movement. For example, if a particular L bend can accommodate 75 mm of movement from a neutral position, cold springing does not allow the L bend to accommodate 150 mm of movement. Analyzing Existing Piping Configurations Piping is best analyzed using a computer stress analysis program, which can provide all pertinent data, including stress, movements, and loads. Services can perform such analysis if programs are not available in house. However, many situations do not require such detailed analysis. A simple, satisfactory method for single and multiplane systems is to divide the system with real or imaginary anchors into a number of single-plane units, as shown in Figure 6, that can be evaluated as L and Z bends. 2. PIPE AND FITTING MATERIALS 2.1 PIPE Steel Pipe Steel pipe is manufactured by several processes. Seamless pipe (Type S), made by piercing or extruding, has no longitudinal seam. Other manufacturing methods roll a strip or sheet of steel (skelp) into a cylinder and weld a longitudinal seam. A continuous-weld (Type F CW) furnace butt-welding (BW; i.e., welding pipe in a single plane) process forces and joins the edges together at high temperature. An electric current welds the seam in electric-resistance-welded (Type E ERW) pipe. ASTM standards such as A53 and A106 specify steel Fig. 6 Multiplane Pipe System pipe A and B grades. The A grade has a lower tensile strength and is not widely used. The ASME pressure piping codes require that a longitudinal joint efficiency factor E (Table 15) be applied to each type of seam when calculating the allowable stress. ASME Standard B36.10M specifies the dimensional standard for wrought steel pipe. Steel pipe is manufactured with wall thicknesses identified by schedule or weight class. Although schedule numbers and weight class designations are related, they are not constant for all pipe sizes. United States standard (STD) and Schedule 40 pipe have the same wall thickness through 250 mm NPS. For 300 mm and larger standard weight pipe, the wall thickness remains constant at 10 mm, whereas Schedule 40 wall thickness increases with each size. A similar equality exists between Extra Strong (XS) and Schedule 80 pipe through 200 mm; above 200 mm, XS pipe has a 12.7 mm wall, whereas Schedule 80 increases in wall thickness. Table 16 lists properties of representative steel pipe. Joints in steel pipe are made by welding or by using threaded, flanged, or grooved fittings or socket welding. Unreinforced welded-in branch connections weaken a main pipeline, and added reinforcement is necessary, unless the excess wall thickness of both mains and branches is sufficient to sustain the pressure. Pipe Design 22.15 Table 15 Allowable Stressesa for Pipe and Tube ASTM Specification Grade A53 steel A53 steel A53 steel A106 steel B88 copper — B B B — Type Manufacturing Process Available Sizes, mm F S E S — Cont. weld Seamless ERW Seamless Hard drawn 15 to 100 15 to 660 50 to 500 15 to 660 8 to 300 Minimum Basic Tensile Allowable Strength, MPa Stress S, MPa 310 413 413 413 248 77.5 103 103 103 62 Joint Efficiency Factor E Allowable Stressb SE, MPa Allowable Stress Rangec SA, MPa 0.6 1.0 0.85 1.0 1.0 46.5 103 87.6 103 62 117 155 155 155 93.1 aListed stresses are for temperatures to 340°C for steel pipe (to 205°C for Type F) and to 120°C for copper tubing. bTo be used for internal pressure stress calculations in Equations (10) and (11). cTo be used only for piping flexibility calculations; see Equations (12) and (13). Licensed for single user. © 2021 ASHRAE, Inc. The ASME Standard B31 series gives formulas and guidelines for determining whether reinforcement is required. Such calculations are seldom needed in HVAC applications because (1) the fitting is designed in accordance with a standard listed in the applicable ASME B31 table and used within the pressure and temperature limits of that standard, and (2) fittings such as tees and reinforced outlet fittings provide integral reinforcement. Type F steel pipe is not allowed for ASME Standard B31.5 refrigerant piping. Copper Tube Because of their inherent resistance to corrosion and ease of installation, copper and copper alloys are often used in heating, airconditioning, refrigeration, and water supply installations. The two main standards for copper tube are (1) ASTM Standard B88, which includes Types K, L, M, and DWV for water and drain service; and (2) ASTM Standard B280, which specifies air-conditioning and refrigeration (ACR) tube for refrigeration service. Types K, L, M, and DWV designate descending wall thicknesses for copper tube. All types have the same outside diameter (OD) for corresponding sizes. Table 17 lists properties of ASTM B88 copper tube. In the plumbing industry, tube of nominal size approximates the inside diameter. The heating and refrigeration trades specify copper tube by the outside diameter. ACR tubing has a different set of wall thicknesses. Types K, L, and M tube may be hard drawn or annealed (soft) temper. Copper tubing is joined with soldered or brazed, wrought or cast copper capillary socket-end fittings. See Table 20 for lists pressure/ temperature ratings of soldered and brazed joints. Small copper tube is also joined by flare or compression fittings. Hard-drawn tubing has a higher allowable stress than annealed tubing, but if hard tubing is joined by soldering or brazing, the annealed allowable stress should be used. Brass pipe and copper pipe are also made in steel pipe thicknesses for threading. High cost has eliminated these materials from the market, except for special applications. The heating and air-conditioning industry generally uses Types L and M tubing, which have higher internal working pressure ratings than the solder joints used at fittings. Type K may be used with brazed joints for higher pressure-temperature requirements or for direct burial. Type M should be used with care where exposed to potential external damage. Copper and brass should not be used in ammonia refrigerating systems, or in acidic drains from condensing boilers. The section on Special Systems covers other limitations on refrigerant piping. Ductile Iron and Cast Iron Cast-iron soil pipe comes as Class 4000 series. It is not used under pressure because the pipe is not suitable and the joints are not restrained. Cast-iron pipe and fittings typically have bell and spigot ends for lead and oakum joints or elastomer push-on joints. Castiron pipe and fittings are also furnished with no-hub ends for joining with no-hub clamps. Local plumbing codes specify permitted materials and joints. Ductile iron has now replaced cast iron for pressure pipe. Ductile iron is stronger, less brittle, and similar to cast iron in corrosion resistance. It is commonly used for buried pressure water mains or in other locations where internal or external corrosion is a problem. Joints are made with flanged fittings, mechanical joint (MJ) fittings, or elastomer gaskets for bell and spigot ends. Bell and spigot and MJ joints are not self-restrained, though restrained MJ systems are available. Ductile-iron pipe is made in seven thickness classes for different service conditions. AWWA Standard C150/A21.50 covers the proper selection of pipe classes. Nonmetallic (Plastic) Selecting a plastic for a specific purpose requires attention to the temperatures, pressures, chemicals, and stresses the piping will be subjected to in the specific application. All are suitable for cold water. Plastic pipe should not be used for compressed gases or compressed air if the pipe’s material is subject to brittle failure. For other liquids and chemicals, refer to charts provided by plastic pipe manufacturers and distributors. Table 18 gives properties of the various plastics discussed in this section; the last column gives the relative cost of small pipe in each category. Table 2 lists some applications pertinent to HVAC. The following are brief descriptions of common uses for the various materials. Plastic piping materials fall into two main categories: thermoplastics and thermosets. Thermoplastics melt and are formed by extruding or molding. They are usually used without reinforcing filaments. Thermosets are cured and cannot be reformed. They are normally used with glass fiber reinforcing filaments. For the purposes of this chapter, thermoplastic piping is made of the following materials: PVC. Because polyvinyl chloride has the best overall range of properties at the lowest cost, it is the most widely used plastic. It is joined by solvent cementing, threading, or flanging. Gasketed pushon joints are also used for larger sizes. ASTM Standards D1784, D1785, and D2665 cover PVC pipe. CPVC. Chlorinated polyvinyl chloride has the same properties as PVC and can withstand a higher temperature before losing strength. It is joined by the same methods as PVC. ASTM Standards D1784 and 1785 discuss CPVC. PE. Low-density polyethylene (LDPE) is a flexible, low-mass tubing with good low-temperature properties. It is used in the food and beverage industry and for instrument tubing. Joins are mechanical, such as compression fittings or push-on connectors and clamps. See ASTM Standard D2239 for details. HDPE. High-density polyethylene is a tough, weather-resistant material used for large pipelines in the gas industry. Fabricated fittings are available. It is joined by heat fusion for large sizes; flare, compression, or insert fittings can be used on small sizes. ASTM Standard D3350 discusses HDPE. 22.16 2021 ASHRAE Handbook—Fundamentals (SI) Table 16 Licensed for single user. © 2021 ASHRAE, Inc. U.S. Surface Area Wall Inside Nominal Nominal Thickness Diameter Outside, Inside, Size, Size, m2/m d, mm m2/m in. mm Schedulea t, mm 1/4 8 3/8 10 1/2 15 3/4 20 1 25 1 1/4 32 1 1/2 40 2 50 2 1/2 65 3 80 4 100 6 150 8 200 10 250 12 300 14 350 16 400 18 450 500 Cross Section Metal Flow Area, Area, mm2 mm2 Working Pressurec ASTM A53 B to 200°C Mass Pipe, kg/m Water, kg/m Mfr. Process Joint Typeb kPa (gage) 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 2.24 3.02 2.31 3.20 2.77 3.73 2.87 3.91 9.25 7.67 12.52 10.74 15.80 13.87 20.93 18.85 0.043 0.043 0.054 0.054 0.067 0.067 0.084 0.084 0.029 0.024 0.039 0.034 0.050 0.044 0.066 0.059 80.6 101.5 107.7 140.2 161.5 206.5 214.6 279.7 67.1 46.2 123.2 90.7 196.0 151.1 344.0 279.0 0.631 0.796 0.844 1.098 1.265 1.618 1.68 2.19 0.067 0.046 0.123 0.091 0.196 0.151 0.344 0.279 CW CW CW CW CW CW CW CW T T T T T T T T 1296 6006 1400 5654 1476 5192 1496 4695 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 3.38 4.55 3.56 4.85 3.68 5.08 3.91 5.54 5.16 7.01 26.64 24.31 35.05 32.46 40.89 38.10 52.50 49.25 62.71 59.00 0.105 0.105 0.132 0.132 0.152 0.152 0.190 0.190 0.229 0.229 0.084 0.076 0.110 0.102 0.128 0.120 0.165 0.155 0.197 0.185 318.6 412.1 431.3 568.7 515.5 689.0 690.3 953 1 099 1 454 557.6 464.1 965.0 827.6 1 313 1 140 2 165 1 905 3 089 2 734 2.50 3.23 3.38 4.45 4.05 5.40 5.43 7.47 8.62 11.40 0.558 0.464 0.965 0.828 1.313 1.140 2.165 1.905 3.089 2.734 CW CW CW CW CW CW CW CW CW CW T T T T T T T T W W 1558 4427 1579 4096 1593 3972 1586 3799 3675 5757 40 ST 80 XS 40 ST 80 XS 40 ST 80 XS 30 40 ST 80 XS 5.49 7.62 6.02 8.56 7.11 10.97 7.04 8.18 12.70 77.93 73.66 102.26 97.18 154.05 146.33 205.0 202.7 193.7 0.279 0.279 0.359 0.359 0.529 0.529 0.688 0.688 0.688 0.245 0.231 0.321 0.305 0.484 0.460 0.644 0.637 0.608 1 438 1 946 2 048 2 844 3 601 5 423 4 687 5 419 8 234 4 769 4 261 8 213 7 417 18 639 16 817 33 000 32 280 29 460 11.27 15.25 16.04 22.28 28.22 42.49 36.73 42.46 64.51 4.769 4.261 8.213 7.417 18.64 16.82 33.01 32.28 29.46 CW CW CW CW ERW ERW ERW ERW ERW W W W W W W W W W 3323 5288 2965 4792 4799 8336 3627 4433 7626 30 40 ST XS 80 30 ST 40 XS 80 7.80 9.27 12.70 15.06 8.38 9.53 10.31 12.70 17.45 257.5 254.5 247.7 242.9 307.1 304.8 303.2 298.5 289.0 0.858 0.858 0.858 0.858 1.017 1.017 1.017 1.017 1.017 0.809 0.800 0.778 0.763 0.965 0.958 0.953 0.938 0.908 6 498 7 683 10 388 12 208 8 307 9 406 10 158 12 414 16 797 52 060 50 870 48 170 46 350 74 060 72 970 72 190 69 940 65 550 50.91 60.20 81.39 95.66 65.09 73.70 79.59 97.28 131.62 52.06 50.87 48.17 46.35 74.06 72.97 72.21 69.96 65.57 ERW ERW ERW ERW ERW ERW ERW ERW ERW W W W W W W W W W 3344 4178 6116 7453 3096 3641 4020 5157 7419 30 ST 40 XS 80 30 ST 40 XS 9.53 11.10 12.70 19.05 9.53 12.70 336.6 333.4 330.2 317.5 387.4 381.0 1.117 1.117 1.117 1.117 1.277 1.277 1.057 1.047 1.037 0.997 1.217 1.197 10 356 12 013 13 681 20 142 11 876 15 708 88 970 87 290 85 610 79 160 117 800 114 000 81.15 94.13 107.21 157.82 93.06 123.09 88.96 87.30 85.63 79.17 117.8 114.0 ERW ERW ERW ERW ERW ERW W W W W W W 3316 3999 4695 7453 2903 4109 ST 9.53 11.10 12.70 14.27 9.53 12.70 15.06 438.2 435.0 431.8 428.7 489.0 482.6 477.9 1.436 1.436 1.436 1.436 1.596 1.596 1.596 1.376 1.367 1.357 1.347 1.536 1.516 1.501 13 396 15 556 17 735 19 863 14 916 19 762 23 325 150 800 148 600 146 450 144 300 187 700 182 900 179 400 104.98 121.90 138.97 155.65 116.88 154.85 182.78 150.8 148.6 146.4 144.3 187.4 182.9 179.4 ERW ERW ERW ERW ERW ERW ERW W W W W W W W 2579 3110 3654 4185 2324 3289 4006 30 20 Steel Pipe Data XS 40 20 ST 30 XS 40 aNumbers are schedule numbers per ASME Standard B36.10M; ST = Standard; XS = Extra Strong. bT = Thread; W = Weld (2)An arbitrary corrosion allowance of 0.64 mm for pipe sizes through NPS 2 and 1.65 mm from NPS 2 1/2 through 20, plus (3) A thread cutting allowance for sizes through NPS 2. cWorking pressures were calculated per ASME Standard B31.9 using furnace butt- weld (continuous weld, CW) pipe through 100 mm and electric resistance weld Because the pipe wall thickness of threaded standard pipe is so small after deducting the (ERW) thereafter. The allowance A has been taken as allowance A, the mechanical strength of the pipe is impaired. It is good practice to limit (1) 12.5% of t for mill tolerance on pipe wall thickness, plus standard threaded pipe pressure to 620 kPa (gage) for steam and 860 kPa (gage) for water. Pipe Design 22.17 Table 17 Copper Tube Data Wall U.S. ThickNominal ness Size, in. Type t, mm 1/4 3/8 1/2 5/8 3/4 1 Licensed for single user. © 2021 ASHRAE, Inc. 1 1/4 1 1/2 2 2 1/2 3 3 1/2 4 5 6 8 10 12 K 0.89 L 0.76 K 1.24 L 0.89 M 0.64 K 1.24 L 1.02 M 0.71 K 1.24 L 1.07 K 1.65 L 1.14 M 0.81 K 1.65 L 1.27 M 0.89 K 1.65 L 1.40 M 1.07 DWV 1.02 K 1.83 L 1.52 M 1.24 DWV 1.07 K 2.11 L 1.78 M 1.47 DWV 1.07 K 2.41 L 2.03 M 1.65 K 2.77 L 2.29 M 1.83 DWV 1.14 K 3.05 L 2.54 M 2.11 K 3.40 L 2.79 M 2.41 DWV 1.47 K 4.06 L 3.18 M 2.77 DWV 1.83 K 4.88 L 3.56 M 3.10 DWV 2.11 K 6.88 L 5.08 M 4.32 DWV 2.77 K 8.59 L 6.35 M 5.38 K 10.29 L 7.11 M 6.45 Diameter Surface Area Outside D, mm Inside d, mm Outside, m2/m Inside, m2/m 9.53 9.53 12.70 12.70 12.70 15.88 15.88 15.88 19.05 19.05 22.23 22.23 22.23 28.58 28.58 28.58 34.93 34.93 34.93 34.93 41.28 41.28 41.28 41.28 53.98 53.98 53.98 53.98 66.68 66.68 66.68 79.38 79.38 79.38 79.38 92.08 92.08 92.08 104.78 104.78 104.78 104.78 130.18 130.18 130.18 130.18 155.58 155.58 155.58 155.58 206.38 206.38 206.38 206.38 257.18 257.18 257.18 307.98 307.98 307.98 7.75 8.00 10.21 10.92 11.43 13.39 13.84 14.45 16.56 16.92 18.92 19.94 20.60 25.27 26.04 26.80 31.62 32.13 32.79 32.89 37.62 38.23 38.79 39.14 49.76 50.42 51.03 51.84 61.85 62.61 63.37 73.84 74.80 75.72 77.09 85.98 87.00 87.86 97.97 99.19 99.95 101.83 122.05 123.83 124.64 126.52 145.82 148.46 149.38 151.36 192.61 196.22 197.74 200.84 240.00 244.48 246.41 287.40 293.75 295.07 0.030 0.030 0.040 0.040 0.040 0.050 0.050 0.050 0.060 0.060 0.070 0.070 0.070 0.090 0.090 0.090 0.110 0.110 0.110 0.110 0.130 0.130 0.130 0.130 0.170 0.170 0.170 0.170 0.209 0.209 0.209 0.249 0.249 0.249 0.249 0.289 0.289 0.289 0.329 0.329 0.329 0.329 0.409 0.409 0.409 0.409 0.489 0.489 0.489 0.489 0.648 0.648 0.648 0.648 0.808 0.808 0.808 0.968 0.968 0.968 0.0244 0.0250 0.0320 0.0344 0.0360 0.0421 0.0436 0.0454 0.0521 0.0530 0.0594 0.0628 0.0646 0.0792 0.0817 0.0841 0.0994 0.1009 0.1030 0.1033 0.1183 0.1201 0.1219 0.1228 0.1564 0.1585 0.1603 0.1628 0.1942 0.1966 0.1990 0.2320 0.2350 0.2378 0.2423 0.2701 0.2733 0.2761 0.3078 0.3115 0.3139 0.3200 0.3834 0.3889 0.3917 0.3975 0.4581 0.4663 0.4694 0.4755 0.6050 0.6163 0.6212 0.6309 0.7541 0.7681 0.7742 0.9028 0.9229 0.9269 Cross Section Metal Flow Area, Area, mm2 mm2 24 21 45 33 24 57 48 34 70 60 106 75 55 139 109 77 173 147 114 108 226 190 157 135 343 292 243 177 487 413 337 666 554 446 281 852 714 596 1084 895 776 478 1610 1266 1108 737 2309 1698 1484 1016 4314 3212 2741 1771 6705 5004 4259 9621 6722 6112 47 50 82 94 103 141 151 164 215 225 281 312 333 502 532 564 785 811 845 850 1 111 1 148 1 181 1 203 1 945 1 997 2 045 2 111 3 004 3 079 3 154 4 282 4 395 4 503 4 667 5 806 5 944 6 063 7 538 7 727 7 846 8 144 11 699 12 042 12 201 12 572 16 701 17 311 17 525 17 993 29 137 30 238 30 710 31 680 45 241 46 942 47 686 64 873 67 771 68 382 Mass Working Pressurea,b,c ASTM B88 to 120°C Tube, kg/m Water, kg/m MPa (gage) Annealed Drawn 0.216 0.188 0.400 0.295 0.216 0.512 0.424 0.302 0.622 0.539 0.954 0.677 0.488 1.249 0.973 0.691 1.543 1.316 1.015 0.967 2.025 1.701 1.399 1.204 3.070 2.606 2.171 1.585 4.35 3.69 3.02 5.96 4.95 3.98 2.51 7.62 6.39 5.33 9.69 8.00 6.94 4.27 14.39 11.32 9.91 6.59 20.64 15.18 13.27 9.09 38.56 28.71 24.50 15.83 59.93 44.73 38.07 85.99 60.09 54.63 0.047 0.050 0.082 0.094 0.103 0.141 0.151 0.164 0.215 0.225 0.281 0.312 0.333 0.502 0.532 0.564 0.785 0.811 0.845 0.850 1.111 1.148 1.182 1.203 1.945 1.997 2.045 2.111 3.004 3.079 3.154 4.282 4.395 4.503 4.667 5.806 5.944 6.063 7.538 7.727 7.846 8.144 11.70 12.04 12.20 12.57 16.70 17.31 17.53 17.99 29.14 30.24 30.71 31.62 45.15 46.94 47.69 64.87 67.77 68.38 5.868 5.033 6.164 4.399 3.144 4.930 4.027 2.820 4.109 3.523 4.668 3.234 2.303 3.634 2.792 1.958 2.972 2.517 1.924 1.827 2.786 2.324 1.896 1.627 2.455 2.069 1.717 1.241 2.275 1.917 1.558 2.193 1.813 1.448 0.903 2.082 1.738 1.441 2.041 1.675 1.448 0.883 1.965 1.531 1.338 0.883 1.972 1.434 1.255 0.855 2.096 1.544 1.317 0.841 2.096 1.551 1.317 2.103 1.455 1.317 11.004 9.432 11.556 8.253 5.895 9.246 7.543 5.282 7.702 6.605 8.757 6.061 4.309 6.812 5.240 3.668 5.571 4.716 3.599 3.427 5.226 4.351 3.558 3.048 4.606 3.951 3.220 2.331 4.268 3.592 2.917 4.109 3.392 2.717 1.696 3.903 3.254 2.703 3.827 3.144 2.717 1.655 3.682 2.875 2.510 1.655 3.696 2.696 2.351 1.600 3.930 2.903 2.468 1.579 3.937 2.910 2.468 3.937 2.724 2.468 aWhen using soldered or brazed fittings, the joint determines the limiting pressure. cIf soldered or brazed fittings are used on hard-drawn tubing, use the annealed ratings. bWorking pressures were calculated using ASME Standard B31.9 allowable stresses. A Full-tube allowable pressures can be used with suitably rated flare or compression-type fittings. 5% mill tolerance has been used on the wall thickness. Higher tube ratings can be calculated using the allowable stress for lower temperatures. 22.18 2021 ASHRAE Handbook—Fundamentals (SI) Table 18 Properties of Pipe Materialsa Material Designation Type and Grade Metals Copper Steel Stainless steel Type L A 53 B 304 Thermoplastics PVC 1120 T I,G1 PVC 1200 T I,G2 PVC 2120 T II,G1 CPVC 4120 T IV,G1 Licensed for single user. © 2021 ASHRAE, Inc. PE 2306 PE 3306 PE 3406 HDPE 3408 PP ABS ABS 1210 ABS 1316 ABS 2112 PVDF Gr. P23 Gr. P34 Gr. P33 Gr. P34 Cell No. Drawn ERW Drawn or Welded 248 413 12454-B 12454-C 14333-D 23447-B 52 14 55 14 355434-C Acrylonitrile 6-3-3 copolymer T I,G2 5-2-2 T I,G3 3-5-5 T II,G1 4-4-5 Thermosetting Epoxy-glass RTRP-11AF PEX A,B,Cd Polyester-glass RTRP-12EF For Comparison Steel A 53 B Copper Type L Hydrostaticb Design Stress, Tensile MPa (at 23°C) Strength, ASME MPa (at B31 23°C) Mfr. ERW Drawn 34 34 38 Upper Temperature Limit, °C HDSb Upper ASME Limit, Mfr. B31 MPa 62 88 11 4.9 14 14 14 14 4.3 4.3 4.3 5.5 60 99 60 100 80 7 11 8.6 48 8.8 138 303 22 303 55 4.3 62 99 93 93 413 248 88 62 Impact Modulus of Coefficient of Thermal Relative Density, Strength, N Elasticity, Expansion, Conductivity, Pipe 3 kg/m (at 23°C) GPa (at 23°C) m/(m·K) W/(m·K) Costc 204 427 177 56 63 8900 7800 7900 1600 66 66 66 99 3.0 1400 2.2 1550 60 70 82 82 99 5.5 82 82 82 135 4.4 6.9 5.5 2.1 82 427 204 960 910 1060 117 190 193 17.1 11.4 17.6 33.5 3.8 1.2 3.5 1.3 43 2.90 2.83 0.159 1.0 80 2.92 54 63 54 63 0.137 2.9 640 70 450 0.62 0.90 1.03 0.76 0.83 1.65 144 126 108 216 108 101 0.389 0.187 0.245 1.1 2.9 3.4 1.72 2.34 0.115 28.0 0.75 1780 200 0.86 99 72 72 142 48 0.54 34 940 200 6.90 0.52 6.90 16 to 23 162 16 to 20 0.418 0.462 0.187 63 56 7800 8900 1600 11.4 17.1 49.6 190 117 1.3 3.5 a Properties listed are for the specific materials listed; each plastic has other formulations. c Based on cost of pipe only, without factoring in fittings, joints, hangers, and Consult the manufacturer of the system chosen. These values are for comparative purposes. b Hydrostatic design stress (HDS) is equivalent to allowable design stress. d A, B, and C are the three manufacturing processes of PEX pipe. The classifica- PP. Polypropylene is a low-mass plastic used for pressure applications and also for chemical waste lines, because it is inert to a wide range of chemicals. A broad variety of drainage fittings are available. For pressure uses, regular fittings are made. It is joined by heat fusion. See ASTM Standards F2830 and F2389 for details. ABS. Acrylonitrile butadiene styrene is a high-strength, impactand weather-resistant material. Some formulations can be used for beverage industry. A wide range of fittings is available. It is joined by solvent cement, threading, or flanging. ASTM Standards D2661 and D3965 cover ABS. PVDF. Polyvinylidene fluoride is widely used for ultrapure water systems and in the pharmaceutical industry and has a wide temperature range. This material is over 20 times more expensive than PVC. It is joined by heat fusion, and fittings are made for this purpose. For smaller sizes, mechanical joints can be used. See ASTM Standard D2122 for information on PVDF. Thermosetting piping used in HVAC is called (1) reinforced thermosetting resin (RTR) and (2) fiberglass-reinforced plastic (FRP). RTR and FRP are interchangeable and refer to pipe and fittings commonly made of (1) fiberglass-reinforced epoxy resin, (2) fiberglassreinforced vinyl ester, and (3) fiberglass-reinforced polyester. Pipe and fittings made from epoxy resin are generally stronger and operate at a higher temperature than those made from polyester or vinyl ester resins, so they are more likely to be used in HVAC. PEX. Cross-linked polyethylene is made from high-density polyethylene (HDPE) and contains cross-linked bonds in the polymer structure. This changes the thermoplastic to a thermoset. It can be used up to 150°C. PEX is used in building services pipework systems, hydronic radiant heating and cooling systems, and domestic water piping. PEX comes in two types: barrier and nonbarrier. The barrier, a thin sheet of aluminum between layers of PEX material or labor. tions are not related to a ranking system. a layer of polymer film, prevents oxygen dissolved in water from diffusing through the pipe and corroding metal components. Nonbarrier PEX is acceptable for plumbing systems. PEX can be ordered as A, B, or C (these designations refer to the manufacturing process and not the pipe’s structural or chemical properties). All PEX tubing (A, B, C) comply with the same standards: refer to ASTM Standards F876, F877, and F2023; CSA Standard B137.5; and NSF/ANSI Standards 14 and 61 for further information. 2.2 FITTINGS Table 19 lists standards that give dimensions and pressure ratings for fittings, flanges, and flanged fittings. These data are also available from manufacturers’ catalogs. 2.3 JOINING METHODS Threading Threading as per ASME Standard B1.202M is the most common method for joining small-diameter steel or brass pipe. Pipe with a wall thickness less than standard should not be threaded. ASME Standard B31.5 limits the threading for various refrigerants and pipe sizes. Soldering and Brazing Copper tube is usually joined by soldering or brazing socket end fittings. Brazing materials melt above 540°C and produce a stronger joint than solder. Table 20 lists soldered and brazed joint strengths. ASME Standard B16.22-specified wrought copper solder joint fittings and ASME Standard B16.18-specified cast copper solder joint fittings are pressure rated the same way as annealed Type L copper Pipe Design 22.19 Table 19 Applicable Standards for Fittings Steela Pipe flanges and flanged fittings Factory-made wrought steel butt-welding fittings Forged fittings, socket-welding and threaded Wrought steel butt-welding short radius elbows and returns Cast Iron, Malleable Iron, Ductile Ironb Cast iron pipe flanges and flanged fittings Malleable iron threaded fittings Gray iron threaded fittings Cast iron threaded drainage fittings ASME Std. B16.5 B16.9 B16.11 B16.9 ASME Std. B16.1 B16.3 B16.4 B16.12 Ductile iron pipe flanges and flanged fittings, Classes 150 and 300 B16.42 ASME Std. Copper and Bronzec Cast bronze threaded fittings, Classes 125 and 25 B16.15 Cast copper alloy solder joint pressure fittings B16.18 Wrought copper and copper alloy solder joint pressure fittings B16.22 Cast copper alloy solder joint drainage fittings, DWV B16.23 Cast copper alloy pipe flanges and flanged fittings, Classes 150, 300, 400, 600, 900, 1500, and 2500 B16.24 Copper and Bronzec(Continued) Cast copper alloy fittings for flared copper tubes ASME Std. B16.26 Wrought copper and wrought copper alloy solder joint drainage fittings B16.29 ASTM Std. Nonmetallicd Threaded PVC plastic pipe fittings, Schedule 80 D2464 Threaded PVC plastic pipe fittings, Schedule 40 D2466 Socket-Type PVC plastic pipe fittings, Schedule 80 D2467 Reinforced epoxy resin gas pressure pipe and fittings D2517 Threaded CPVC plastic pipe fittings, Schedule 80 F437 Socket-Type CPVC plastic pipe fittings, Schedule 40 F438 Socket-Type CPVC plastic pipe fittings, Schedule 80 F439 Insert fittings for PEX tubing F877 Plastic brass, bronze, and copper insert fittings for PEX tubing F877 Solvent cements for PVC plastic piping systems D2564 Solvent cements for CPVC plastic pipe and fittings F493 Licensed for single user. © 2021 ASHRAE, Inc. aWrought steel butt-welding fittings are made to match steel pipe wall thicknesses and are rated at the same working pressure as seamless pipe. Flanges and flanged fittings are rated by working steam pressure classes. Forged steel fittings are rated from 14 to 41 MPa in classes and are used for high-temperature and high-pressure service for small pipe sizes. bClass numbers refer to maximum working saturated steam gage pressure (in pounds per square inch. Multiply these values by 6.9 to convert to kilopascals). For liquids at lower temperatures, higher pressures are allowed. Groove-end fittings of these materials are made by various manufacturers who publish their own ratings. cClasses refer to maximum working steam gage pressure (in pounds per square inch. Multiply these values by 6.9 to convert to kilopascals). At ambient temperatures, higher liquid pressures are allowed. Solder joint fittings are limited by the strength of the soldered or brazed joint (see Table 20). dRatings of plastic fittings match the pipe of corresponding schedule number. Table 20 Internal Working Pressure for Copper Tube Joints Internal Working Pressure, kPa Sat. Steam and Condensate Water and Noncorrosive Liquids and Gasesa Service Temperature, °C 8 to 25 32 to 50 65 to 100 125 to 200a 250 to 300a 8 to 200 38 66 93 120 1380 1030 690 590 1210 860 620 520 1030 690 520 350 900 620 480 310 690 480 350 280 — — — 100 95-5 tin/antimonyc solder (ASTM B32 Gr 50TA) 38 66 93 120 3450 2760 2070 1380 2760 2410 1720 1200 2070 1900 1380 1030 1860 1720 1240 930 1030 1030 970 760 — — — 100 Brazing alloys melting at or above 540°C 38 to 93 120 175 d d d d d 2070 1860 1450 1310 1170 1030 1030 1030 1030 1030 — — 830 Alloy Used for Joints 50-50 tin/leadb solder (ASTM B32 Gr 50A) Nominal Tube Size (Types K, L, M), mm Source: Based on ASME Standard B31.9 aSolder joints are not to be used for (1) Flammable or toxic gases or liquids (2) Gas, vapor, or compressed air in tubing over 100 mm, unless maximum pressure is limited to 140 kPa (gage). tube of the same size. Health concerns have caused many jurisdictions to ban solder containing lead or antimony for joining pipe in potable-water systems. Lead-based solder, in particular, must not be used for potable water. Flared and Compression Joints Flared and compression fittings can be used to join copper, steel, stainless steel, and aluminum tubing. Properly rated fittings can keep the joints as strong as the tube. bLead solders must not be used in potable-water systems. c Tin/antimony solder is allowed for potable-water supplies in some jurisdic- tions. dRated pressure for temperatures up to 93°C is that of the tube being joined. Flanges Flanges can be used for large pipe and all piping materials. They are commonly used to connect to equipment and valves, and wherever the joint must be opened to allow service or replacement of components. For steel pipe, flanges are available in pressure ratings to 17 MPa. High-tensile-strength bolts must be used for highpressure flanged joints. For welded pipe, weld neck, slip-on, or socket weld flanges are available. Thread-on flanges are available for threaded pipe. 22.20 Flanges are generally flat faced or raised face. Flat-faced flanges with full-faced gaskets are most often used with cast iron and materials that cannot take high bending loads. Raised-face flanges with ring gaskets are preferred with steel pipe because they facilitate increasing the sealing pressure on the gasket to help prevent leaks. Other facings, such as O ring and ring joint, are available for special applications. All flat-faced, raised-face, and lap-joint flanges require a gasket between the mating flange surfaces. Gaskets are made from rubber, synthetic elastomers, cork, fiber, plastic, polytetrafluoroethylene (PTFE), metal, and combinations of these materials. The gasket must be compatible with the flowing media and the temperatures at which the system operates. Licensed for single user. © 2021 ASHRAE, Inc. Welding Welded-steel pipe joints offer the following advantages: • Do not age, dry out, or deteriorate as gasketed joints do • Can accommodate greater vibration and water hammer and higher temperatures and pressures than other joints • For critical service, can be tested by several nondestructive examination (NDE) methods, such as radiography or ultrasound • Provide maximum long-term reliability The applicable sections of the ASME Standard B31 series and the ASME Boiler and Pressure Vessel Code give rules for welding. ASTM Standard B31 requires that all welders and welding procedure specifications (WPS) be qualified. Separate WPS are needed for different welding methods and materials. The qualifying tests and the variables requiring separate procedure specifications are set forth in the ASME Boiler and Pressure Vessel Code, Section IX. The manufacturer, fabricator, or contractor is responsible for the welding procedure and welders. ASME Standard B31.9 requires visual examination of welds and outlines limits of acceptability. The following welding processes are often used in the HVAC industry: • Shielded metal arc welding (SMAW), also called stick welding): the molten weld metal is shielded by vaporization of the electrode coating. • Gas metal arc welding (GMAW), also called metal inert gas (MIG) welding: the electrode is a continuously fed wire shielded by argon or carbon dioxide gas from the welding gun nozzle. • Gas tungsten arc welding (GTAW), also called tungsten insert gas (TIG) welding: this process uses a nonconsumable tungsten electrode surrounded by a shielding gas. The weld material may be provided from a separate noncoated rod. Integrally Reinforced Outlet Fittings Integrally reinforced outlet fittings are used to make branch and take-off connections and are designed to allow welding directly to pipe without supplemental reinforcing. Fittings are available with threaded, socket welded, or butt-weld outlets. Solvent Cement Solvent cement welds nonmetallic pipe together by softening surface of the materials being joined. It is different from gluing, which hardens and holds the material together. Sometimes this join is called a solvent-welded joint. Rolled-Groove Joints Grooved joints require special grooved fittings and a shallow groove cut or rolled into the pipe end. These joints can be used with steel, cast iron, ductile iron, copper, and plastic pipes. A segmented clamp engages the grooves and a special gasket uses internal pressure to tighten the seal. Some clamps are designed with clearance between tongue and groove to accommodate misalignment and thermal movements, and others are designed to limit movement and 2021 ASHRAE Handbook—Fundamentals (SI) provide a rigid system. Manufacturers’ data give temperature and pressure limitations. Bell-and-Spigot Joints A bell-and-spigot joint is mechanical joint consists of a sleeve slightly larger than the outside diameter of the pipe. The pipe ends are inserted into the sleeve, and gaskets are packed into the annular space between the pipe and coupling and held in place by retainer rings. This type of joint can accept some axial misalignment, but it must be anchored or otherwise restrained to prevent axial pullout or lateral movement. Manufacturers provide pressure/temperature data. Press-Connect (Press Fit) Joints These joints rely on an elastomeric gasket or seal and an approved pressing tool and jaws to seal the joint. Push-Connect Joints Push-connect joining use and integral elastomeric seal or gasket and stainless steel ring to make a leak-free joint. There are two common types, both of which form strong, permanent joints: one type is removable for servicing, and the other type is not easily removed after installation. Unions Unions allow disassembly of threaded pipe systems. Unions are three-part fittings with a mating machined seat on the two parts that thread onto the pipe ends. A threaded locking ring holds the two ends tightly together. A union also allows threaded pipe to be turned at the last joint connecting two pieces of equipment. Companion flanges (a pair) for small pipe serve the same purpose. 2.4 EXPANSION JOINTS AND EXPANSION COMPENSATING DEVICES Although the inherent flexibility of the piping should be used to the maximum extent possible, expansion joints must be used where movements are too large to accommodate with pipe bends or loops or where insufficient room exists to construct a loop of adequate size. Typical situations are tunnel piping and risers in high-rise buildings, especially for steam and hot-water pipes where large thermal movements are involved. Packed and packless expansion joints and expansion compensating devices are used to accommodate movement, either axially or laterally. In the axial method of accommodating movement, the expansion joint is installed between anchors in a straight-line segment and accommodates axial motion only. This method has high anchor loads, primarily because of pressure thrust. It requires careful guiding, but expansion joints can be spaced conveniently to limit movement of branch connections. The axial method finds widest application for long runs without natural offsets, such as tunnel and underground piping and risers in tall buildings. The lateral or offset method requires the device to be installed in a leg perpendicular to the expected movement and accommodates lateral movement only. This method generally has low anchor forces and minimal guide requirements. It finds widest application in lines with natural offsets, especially where there are few or no branch connections. Packed expansion joints depend on slipping or sliding surfaces to accommodate the movement and require some type of seals or packing to seal the surfaces. Most such devices require some maintenance but are not subject to catastrophic failure. Further, with most packed expansion joint devices, any leaks that develop can be repacked under full line pressure without shutting down the system. Packless expansion joints depend on the flexing or distortion of the sealing element to accommodate movement. They generally do Pipe Design 22.21 Licensed for single user. © 2021 ASHRAE, Inc. Fig. 7 Packed Slip Expansion Joint not require any maintenance, but maintenance or repair is not usually possible. If a leak occurs, the system must be shut off and drained, and the entire device must be replaced. Further, catastrophic failure of the sealing element can occur and, although likelihood of such failure is remote, it must be considered in certain design situations. Packed expansion joints are preferred where long-term system reliability is of prime importance (using types that can be repacked under full line pressure) and where major leaks can be life threatening or extremely costly. Typical applications are risers, tunnels, underground pipe, and distribution piping systems. Packless expansion joints are generally used where even small leaks cannot be tolerated (e.g., for gas and toxic chemicals), where temperature limitations preclude the use of packed expansion joints, and for very-largediameter pipe where packed expansion joints cannot be constructed or the cost would be excessive. In all cases, expansion joints should be installed, anchored, and guided in accordance with expansion joint manufacturers’ recommendations. joint from the system. The packing technology of the packed slip expansion joint, explained previously, has been incorporated into the flexible ball joint design; now, packed flexible ball joints have self-lubricating semiplastic packing that can be injected under full line pressure without shutting off the system (Figure 8). Standard flexible ball joints are available in sizes 32 to 760 mm with threaded (32 to 50 mm), weld, and flange ends for pressures to 2.1 MPa and temperatures to 400°C. Flexible ball joints are available in larger sizes and for higher temperature and pressure ranges. Packed Expansion Joints Packless Expansion Joints There are two types of packed expansion joints: packed slip expansion joints and flexible ball joints. Packed Slip Expansion Joints. These are telescoping devices designed to accommodate axial movement only. Packing seals the sliding surfaces. The original packed slip expansion joint used multiple layers of braided compression packing, similar to the stuffing box commonly used with valves and pumps; this arrangement requires shutting and draining the system for maintenance and repair. Advances in design and packing technology have eliminated these problems, and most current packed slip joints use selflubricating semiplastic packing, that can be injected under full line pressure without shutting off the system (Figure 7). (Many manufacturers use asbestos-based packings, unless requested otherwise. Asbestos-free packings, such as flake graphite, are available and, although more expensive, should be specified in lieu of products containing asbestos.) Standard packed slip expansion joints are constructed of carbon steel with weld or flange ends in sizes 40 to 910 mm for pressures up to 2.1 MPa and temperatures up to 425°C. Larger, highertemperature, and higher-pressure designs are available. Standard single joints are generally designed for 100, 200, or 300 mm axial traverse; double joints with an intermediate anchor base can accommodate twice these movements. Special designs for greater movements are available. Flexible Ball Joints. These joints are used in pairs to accommodate lateral or offset movement and must be installed in a leg perpendicular to the expected movement. The original flexible ball joint design incorporated only inner and outer containment seals that could not be serviced or replaced without removing the ball Types include metal bellows expansion joints, rubber expansion joints, and flexible hose or pipe connectors. Metal Bellows Expansion Joints. These expansion joints have a thin-walled convoluted section that accommodates movement by bending or flexing. The bellows material is generally Type 304, 316, or 321 stainless steel, but other materials are commonly used to satisfy service conditions. Small-diameter expansion joints 20 to 80 mm are generally called expansion compensators and are available in all-bronze or steel construction. Metal bellows expansion joints can generally be designed for the pressures and temperatures commonly encountered in HVAC systems and can also be furnished in rectangular configurations for ducts and chimney connectors. Overpressurization, improper guiding, and other forces can distort the bellows element. For low-pressure applications, such distortion can be controlled by the geometry of the convolution or the thickness of the bellows material. For higher pressure, internally pressurized joints require reinforcing. Externally pressurized designs are not subject to such distortion and are not generally furnished without supplemental bellows reinforcing. Single- and double-bellows expansion joints primarily accommodate axial movement only, similar to packed slip expansion joints. Although bellows expansion joints can accommodate some lateral movement, the universal tied bellows expansion joint better accommodates large lateral movement. This device operates much like a pair of flexible ball joints, except that bellows elements are used instead of flexible ball elements. The tie rods on this joint contain the pressure thrust, so anchor loads are much lower than with axial-type expansion joints. Fig. 8 Flexible Ball Joint 22.22 2021 ASHRAE Handbook—Fundamentals (SI) Table 21 Piping System Design Maximum Flow Rate for Energy Conservationa,b 2000 Operating Hours/year Pipe Size, mm Nominal Other IPS Sched. 40 Std. ID 63 76 102 127 152 203 255 305 305 62.7 77.9 102.3 128.2 153.8 202.7 254.5 303.2 2000 and 4400 Variable Flow/ Variable Speed 4400 Variable Flow/ Variable Speed Other Variable Flow/ Variable Speed Other L/s m/s L/s m/s L/s m/s L/s m/s L/s m/s L/s m/s 7.57 11.35 22.08 25.87 47.32 75.71 113.55 157.72 NA 2.5 2.5 2.7 2.0 2.5 2.3 2.2 2.2 2.5 11.35 17.03 33.45 39.12 64.00 113.55 170.35 239.75 NA 3.7 3.5 4.1 3.0 3.7 3.5 3.3 3.3 4.0 5.35 8.83 16.40 19.55 39.55 56.78 82.02 119.87 NA 1.7 1.8 2.0 1.5 1.9 1.8 1.5 1.7 2.0 8.20 13.25 25.25 29.65 54.25 88.33 126.18 182.95 NA 2.5 2.8 3.1 2.3 2.9 2.7 2.5 2.5 2.9 4.29 6.95 13.25 15.77 27.75 44.15 63.09 94.65 NA 1.5 1.5 1.5 1.2 1.5 1.5 1.2 1.3 1.5 6.95 10.72 20.19 23.35 42.90 69.40 100.95 145.11 NA 2.2 2.2 2.5 1.8 2.3 2.1 2.0 2.0 2.3 aSource: Based on ASHRAE Standard 90.1-2013 Table 6.5.4.5 with the addition of IPS and calculation for velocity in metres per second. bThis table does not apply to district energy systems, and velocities in larger-bore piping can exceed these values per an interpretation of the ASHRAE 90.1 committee. Licensed for single user. © 2021 ASHRAE, Inc. Table 22 Water Velocities Based on Type of Service Table 23 Maximum Water Velocity to Minimize Erosion Type of Service Velocity, m/s Reference Normal Operation, h/yr Water Velocity, m/s General service City water 1.2 to 3.0 0.9 to 2.1 0.6 to 1.5 1.8 to 4.6 1.2 to 2.1 a, b, c a, b c a, c a, b 1500 2000 3000 4000 6000 4.6 4.4 4.0 3.7 3.0 Boiler feed Pump suction and drain lines a Crane Co. (1976). b Carrier (1960). c Grinnell Company (1951). Rubber Expansion Joints. Similar to single-metal bellows expansion joints, rubber expansion joints incorporate a nonmetallic elastomeric bellows sealing element and generally have more stringent temperature and pressure limitations. Although rubber expansion joints can be used to accommodate expansion and contraction of the piping, they are primarily used as flexible connectors at equipment to isolate sound and vibration and eliminate stress at equipment nozzles. Flexible Hose. This type of hose can be constructed of elastomeric material or corrugated metal with an outer braid for reinforcing and end restraint. Flexible hose is primarily used as a flexible connector at equipment to isolate sound and vibration and eliminate stress at equipment nozzles; however, flexible metal hose is well suited for use as an offset-type expansion joint, especially for copper tubing and branch connections off risers. 3. APPLICATIONS 3.1 WATER PIPING Flow Rate Limitations Stewart and Dona (1987) surveyed the literature relating to water flow rate limitations. Noise, erosion, and installation and operating costs all limit the maximum and minimum velocities in piping systems. If piping sizes are too small, noise levels, erosion levels, and pumping costs can be unfavorable. If piping sizes are too large, installation costs are excessive. Therefore, pipe sizes are chosen to minimize initial cost while avoiding the undesirable effects of high velocities. ASHRAE Standard 90.1 has been accepted by authorities having jurisdiction (AHJs) as a code and, as such, limits the flow for energy conservation. The table (Table 21) is reproduced with modification showing velocity limitations. Various upper limits of water velocity and/or pressure drop in piping and piping systems are used. One recommendation places a velocity limit of 1.2 m/s for 50 mm pipe and smaller, and a pressure drop limit of 400 Pa/m for piping over 50 mm. Other guidelines are based on the type of service (Table 22) or annual operating hours Source: Carrier (1960). (Table 23). These limitations are imposed either to control the levels of pipe and valve noise, erosion, and water hammer pressure or for economic reasons. Carrier (1960) recommends that the velocity not exceed 4.6 m/s in any case. Noise Generation Velocity-dependent noise in piping and piping systems results from any or all of four sources: turbulence, cavitation, release of entrained air, and water hammer. In investigations of flow-related noise, Ball and Webster (1976), Marseille (1965), and Rogers (1953, 1954, 1956) reported that velocities on the order of 3 to 5 m/s lie within the range of allowable noise levels for residential and commercial buildings. The experiments showed considerable variation in noise levels obtained for a specified velocity. Generally, systems with longer pipe and with more numerous fittings and valves were noisier. In addition, sound measurements were taken under widely differing conditions; for example, some tests used plastic-covered pipe, whereas others did not. Thus, no detailed correlations relating sound level to flow velocity in generalized systems are available. Noise generated by fluid flow in a pipe increases sharply if cavitation or release of entrained air occurs. Usually, the combination of high water velocity with a change in flow direction or a decrease in pipe cross section, causing a sudden pressure drop, is necessary to cause cavitation. Ball and Webster (1976) found that at their maximum velocity of 13 m/s, cavitation did not occur in straight 10 and 15 mm pipe; using the apparatus with two elbows, cold-water velocities up to 6.5 m/s caused no cavitation. Cavitation did occur in orifices of 1:8 area ratio (orifice flow area is one-eighth of pipe flow area) at 1.5 m/s and in 1:4 area ratio orifices at 3 m/s (Rogers 1954). Some data are available for predicting hydrodynamic (liquid) noise generated by control valves. The International Society of Automation compiled prediction correlations in an effort to develop control valves for reduced noise levels (ISA 2007). The correlation to predict hydrodynamic noise from control valves is SL = 10 log Av + 20 log p – 30 log t + 76.6 (20) Pipe Design where SL = sound level, dB Av = valve coefficient, m3/(s·Pa)0.5 Q = flow rate, m3/s p = pressure drop across valve, Pa t = downstream pipe wall thickness, mm Air entrained in water usually has a higher partial pressure than the water. Even when flow rates are small enough to avoid cavitation, the release of entrained air may create noise. Every effort should be made to vent the piping system or otherwise remove entrained air. Erosion Erosion in piping systems is caused by water bubbles, sand, or other solid matter impinging on the inner surface of the pipe. Generally, at velocities lower than 3 m/s, erosion is not significant as long as there is no cavitation. When solid matter is entrained in the fluid at high velocities, erosion occurs rapidly, especially in bends. Thus, high velocities should not be used in systems where sand or other solids are present or where slurries are transported. Licensed for single user. © 2021 ASHRAE, Inc. Allowances for Aging With age, the internal surfaces of pipes become increasingly rough. This reduces the available flow with a fixed pressure supply. However, designing with excessive age allowances may result in oversized piping. Age-related decreases in capacity depend on type of water, type of pipe material, temperature of water, and type of system (open or closed) and include • Sliming (biological growth or deposited soil on the pipe walls): occurs mainly in unchlorinated, raw water systems. • Caking of calcareous salts: occurs in hard water (i.e., water bearing calcium salts) and increases with water temperature. • Corrosion (incrustations of ferrous and ferric hydroxide on the pipe walls): occurs in metal pipe in soft water. Because oxygen is necessary for corrosion to take place, significantly more corrosion takes place in open systems. Allowances for expected decreases in capacity are sometimes treated as a specific amount (percentage). Dawson and Bowman (1933) added an allowance of 15% friction loss to new pipe (equivalent to an 8% decrease in capacity). The HDR Design Guide (1981) increased the friction loss by 15 to 20% for closed piping systems and 75 to 90% for open systems. Carrier (1960) indicates a factor of approximately 1.75 between friction factors for closed and open systems. Obrecht and Pourbaix (1967) differentiated between the corrosive potential of different metals in potable water systems and concluded that iron is the most severely attacked, then galvanized steel, lead, copper, and finally copper alloys (e.g., brass). Freeman (1941) and Hunter (1941) showed the same trend. After four years of coldand hot-water use, copper pipe had a capacity loss of 25 to 65%. Aged ferrous pipe has a capacity loss of 40 to 80%. Smith (1983) recommended increasing the design discharge by 1.55 for uncoated cast iron, 1.08 for iron and steel, and 1.06 for cement or concrete. The Plastic Pipe Institute (1971) found that corrosion is not a problem in plastic pipe; the capacity of plastic pipe in Europe and the United States remains essentially the same after 30 years in use. Extensive age-related flow data are available for use with the Hazen-Williams empirical equation. Difficulties arise in its application, however, because the original Hazen-Williams roughness coefficients are valid only for the specific pipe diameters, water velocities, and water viscosities used in the original experiments. Thus, when the Cs are extended to different diameters, velocities, and/or water viscosities, errors of up to about 50% in pipe capacity can occur (Sanks 1978; Williams and Hazen 1933). 22.23 Water Hammer When any moving fluid (not just water) is abruptly stopped, as when a valve closes suddenly, large pressures can develop. Although detailed analysis requires knowledge of the elastic properties of the pipe and the flow-time history, the limiting case of rigid pipe and instantaneous closure is simple to calculate. Under these conditions, ph = csV (21) where ph = pressure rise caused by water hammer, Pa = fluid density, kg/m3 cs = velocity of sound in fluid, m/s V = fluid flow velocity, m/s The cs for water is 1439 m/s, although the pipe’s elasticity reduces the effective value. Example 3. What is the maximum pressure rise if water flowing at 3 m/s is stopped instantaneously? Solution: ph = 1000 1439 3 = 4.32 MPa 3.2 SERVICE WATER PIPING Sizing service water piping differs from sizing process lines in that design flows in service water piping are determined by the probability of simultaneous operation of multiple individual loads such as water closets, urinals, lavatories, sinks, and showers. The full-flow characteristics of each load device are readily obtained from manufacturers; however, service water piping sized to handle all load devices simultaneously would be seriously oversized. Thus, a major issue in sizing service water piping is to determine the diversity of the loads. The procedure shown in this chapter uses the work of R.B. Hunter for estimating diversity (Hunter 1940, 1941). The present-day plumbing designer is usually constrained by building or plumbing codes, which specify the individual and collective loads to be used for pipe sizing. Frequently used codes (including the ICC International Plumbing Code and the PHCC National Standard Plumbing Code) contain procedures quite similar to those shown here. The designer must be aware of the applicable code for the location being considered. Federal mandates are forcing plumbing fixture manufacturers to reduce design flows to many types of fixtures, but these may not yet be included in locally adopted codes. Also, the designer must be aware of special considerations; for example, toilet usage at sports arenas will probably have much less diversity than codes allow and thus may require larger supply piping than the minimum specified by codes. Table 24 gives the rate of flow desirable for many common fixtures and the average pressure necessary to give this rate of flow. Pressure varies with fixture design. In estimating load, the rate of flow is frequently computed in fixture units that are relative indicators of flow. Table 25 gives the demand weights in terms of fixture units for different plumbing fixtures under several conditions of service, and Figure 9 gives the estimated demand corresponding to any total number of fixture units. Figures 10 and 11 provide more accurate estimates at the lower end of the scale. The estimated demand load for fixtures used intermittently on any supply pipe can be obtained by multiplying the number of each kind of fixture supplied through that pipe by its weight from Table 25, adding the products, and then referring to the appropriate curve of Figure 9, 10, or 11 to find the demand corresponding to the total fixture units. In using this method, note that the demand for fixture or supply outlets other than those listed in the table of fixture units is not yet included in the estimate. The demands for outlets (e.g., hose connections and air-conditioning apparatus) that are likely to impose 22.24 2021 ASHRAE Handbook—Fundamentals (SI) Table 24 Proper Flow and Pressure Required During Flow for Different Fixtures Flow Pressure, kPa (gage)a Flow, L/s Fixture Ordinary basin faucet Self-closing basin faucet Sink faucet, 10 mm Sink faucet, 15 mm Dishwasher Bathtub faucet Laundry tube cock, 8 mm Shower Ball cock for closet Flush valve for closet Flush valve for urinal Garden hose, 15 m, and sill cock 55 85 70 35 105 to 175 35 35 85 105 70 to 140 105 210 0.2 0.2 0.3 0.3 —b 0.4 0.3 0.2 to 0.6 0.2 1.0 to 2.5c 1.0 0.3 a Flow pressure is that in pipe at entrance to fixture. b Varies; see manufacturers’ data. c Wide range because of variation in design and type of flush valve closets. Licensed for single user. © 2021 ASHRAE, Inc. Table 25 Demand Weights of Fixtures in Fixture Unitsa Fixture or Groupb Occupancy Water closet Public Type of Supply Control Flush valve Flush tank Pedestal urinal Public Flush valve Stall or wall urinal Public Flush valve Flush tank Lavatory Public Faucet Bathtub Public Faucet Shower head Public Mixing valve Service sink Office, etc. Faucet Kitchen sink Hotel or restaurant Faucet Water closet Private Flush valve Flush tank Lavatory Private Faucet Bathtub Private Faucet Shower head Private Mixing valve Bathroom group Private Flush valve for closet Flush tank for closet Separate shower Private Mixing valve Kitchen sink Private Faucet Laundry trays (1 to 3) Private Faucet Combination fixture Private Faucet Weight in Fixture Unitsc 10 5 10 5 3 2 4 4 3 4 6 3 1 2 2 8 6 2 2 3 3 Fig. 9 Demand Versus Fixture Units, Mixed System, High Part of Curve (Adapted from Hunter 1941) Source: Hunter (1941). a For supply outlets likely to impose continuous demands, estimate continuous supply separately, and add to total demand for fixtures. b For fixtures not listed, weights may be assumed by comparing fixture to listed one using water in similar quantities and at similar rates. c Given weights are for total demand. For fixtures with both hot- and cold-water supplies, weights for maximum separate demands can be assumed to be 75% of listed demand for the supply. continuous demand during heavy use of the weighted fixtures should be estimated separately and added to demand for fixtures used intermittently to estimate total demand. The Hunter curves in Figures 9, 10, and 11 are based on use patterns in residential buildings and can be erroneous for other usages such as sports arenas. Williams (1976) discusses the Hunter assumptions and presents an analysis using alternative assumptions. So far, the information presented shows the design rate of flow to be determined in any particular section of piping. The next step is to determine the size of piping. As water flows through a pipe, the pressure continually decreases along the pipe because of loss of energy from friction. The problem is then to ascertain the minimum pressure in the street main and the minimum pressure required to operate the topmost fixture. (A pressure of 100 kPa may be ample for most flush valves, but manufacturers’ requirements should be consulted. Some fixtures require a pressure up to 175 kPa. A minimum of 55 kPa should be allowed for other fixtures.) The pressure differential Fig. 10 Estimate Curves for Demand Load (Adapted from Hunter 1941) overcomes pressure losses in the distributing system and the difference in elevation between the water main and the highest fixture. The pressure loss (in kPa) resulting from the difference in elevation between the street main and the highest fixture can be obtained by multiplying the difference in elevation in metres by the conversion factor 9.8. Pressure losses in the distributing system consist of pressure losses in the piping itself, plus the pressure losses in the pipe fittings, valves, and the water meter, if any. Approximate design pressure losses and flow limits for disk-type meters for various rates of flow are given in Figure 12. Water authorities in many localities Pipe Design 22.25 Licensed for single user. © 2021 ASHRAE, Inc. Fig. 11 Section of Figure 10 on Enlarged Scale Fig. 13 Variation of Pressure Loss with Flow Rate for Various Faucets and Cocks Fig. 12 Pressure Losses in Disk-Type Water Meters require compound meters for greater accuracy with varying flow; consult the local utility. Design data for compound meters differ from the data in Figure 12. Manufacturers give data on exact pressure losses and capacities. Figure 13 shows the variation of pressure loss with rate of flow for various faucets and cocks. The water demand for hose bibbs or other large-demand fixtures taken off the building main frequently results in inadequate water supply to the upper floor of a building. This condition can be prevented by sizing the distribution system so that pressure drops from the street main to all fixtures are the same. An ample building main (not less than 25 mm where possible) should be maintained until all branches to hose bibbs have been connected. Where street main pressure is excessive and a pressure-reducing valve is used to prevent water hammer or excessive pressure at fixtures, hose bibbs should be connected ahead of the reducing valve. The principles involved in sizing upfeed and downfeed systems are the same. In the downfeed system, however, the difference in elevation between the overhead supply mains and the fixtures provides the pressure required to overcome pipe friction. Because friction pressure loss and height pressure loss are not additive, as in an upfeed system, smaller pipes may be used with a downfeed system. Plastic Pipe The maximum safe water velocity in a thermoplastic piping system under most operating conditions is typically 1.5 m/s; however, higher velocities can be used in cases where the operating characteristics of valves and pumps are known so that sudden changes in flow velocity can be controlled. The total pressure in the system at any time (operating pressure plus surge of water hammer) should not exceed 150% of the pressure rating of the system. Procedure for Sizing Cold-Water Systems The recommended procedure for sizing piping systems is as follows: 1. Sketch the main lines, risers, and branches, and indicate the fixtures to be served. Indicate the rate of flow of each fixture. 2. Using Table 25, compute the demand weights of the fixtures in fixture units. 3. Determine the total demand in fixture units and, using Figure 9, 10, or 11, find the expected demand. 4. Determine the equivalent length of pipe in the main lines, risers, and branches. Because the sizes of the pipes are not known, the exact equivalent length of various fittings cannot be determined. Add the equivalent lengths, starting at the street main and proceeding along the service line, main line of the building, and up the riser to the top fixture of the group served. 5. Determine the average minimum pressure in the street main and the minimum pressure required for operation of the topmost fixture, which should be 50 to 175 kPa above atmospheric. 6. Calculate the approximate design value of the average pressure drop per unit length of pipe in equivalent length determined in step 4 and using Equation (1). p = ( ps – 9.8H – pf – pm)/L where p = average pressure loss per metre of equivalent length of pipe, kPa ps = pressure in street main, kPa pf = minimum pressure required to operate topmost fixture, kPa pm = pressure drop through water meter, kPa H = height of highest fixture above street main, m L = equivalent length determined in step 4, m If the system is downfeed supply from a gravity tank, height of water in the tank, converted to kPa by multiplying by 9.8, replaces the street main pressure, and the term 9.8H is added 22.26 2021 ASHRAE Handbook—Fundamentals (SI) instead of subtracted in calculating p. In this case, H is the vertical distance of the fixture below the bottom of the tank. The pressure conversion factor 9.8 is determined by the mass of water occupying a 1 m3 volume, or 9800 N/m2 (9.8 kPa/m). 7. From the expected rate of flow determined in step 3 and the value of p calculated in step 6, choose the sizes of pipe from Figure 14, 15, or 16. Example 4. Assume a minimum street main pressure of 375 kPa; a height of topmost fixture (a urinal with flush valve) above street main of 15 m; an equivalent pipe length from water main to highest fixture of 30 m; a total load on the system of 50 fixture units; and that the water closets are flush valve operated. Find the required size of supply main. Solution: Use Equation (1): p = ( ps – 9.8H – pf – pm)/L ps = Street main pressure (given) = 375 kPa H = 15 m (given) Pf = 105 kPa from Table 24 Flow = 3.2 L/s from Figure 11 Licensed for single user. © 2021 ASHRAE, Inc. For a trial run, use 40 mm; then Pm = 45 kPa from Figure 12 at 3.2 L/s. The pressure drop available for overcoming friction in pipes and fittings is 375 – 9.8 15 – 105 – 45 = 78 kPa. At this point, estimate the equivalent pipe length of the fittings on the direct line from the street main to the highest fixture. The exact equivalent length of the various fittings cannot be determined because the pipe sizes of the building main, riser, and branch leading to the highest fixture are not yet known, but a first approximation is necessary to tentatively select pipe sizes. If the computed pipe sizes differ from those used in determining the equivalent length of pipe fittings, a recalculation using the computed pipe sizes for the fittings will be necessary. It is common practice for the first trial to assume that the total equivalent length of the pipe fittings is 50% of the total length of pipe. In this example, 30 m 50% = 15 m. The permissible pressure loss per metre of equivalent pipe is 78/(30 + 15) = 1.7 kPa/m. A 40 mm building main is adequate. The sizing of the branches of the building main, the risers, and the fixture branches follows these principles. For example, assume that one of the branches of the building main carries the cold-water supply for three water closets, two bathtubs, and three lavatories. Using the permissible pressure loss of 1.7 kPa/m, the size of branch (determined from Table 25 and Figures 14 and 11) is found to be 40 mm. Items included in the computation of pipe size are as follows: Table 26 is a guide to minimum pipe sizing where flush valves are used. Fig. 14 Fixtures, No. and Type Fixture Units (Table 25 and Note c) 3 flush valves 2 bathtubs 3 lavatories Total 36 = 18 0.75 2 2 = 3 0.75 3 1 = 2.25 = 23.25 Demand Pipe Size (Figure 11) (Figure 14) 2.4 L/s 40 mm Velocities exceeding 3 m/s cause undesirable noise in the piping system. This usually governs the size of larger pipes in the system, whereas in small pipe sizes, the friction loss usually governs the selection because the velocity is low compared to friction loss. Velocity is the governing factor in downfeed systems, where friction loss is usually neglected. Velocity in branches leading to pump suctions should not exceed 1.5 m/s. If the street pressure is too low to adequately supply upper-floor fixtures, the pressure must be increased. Constant- or variable-speed booster pumps, alone or in conjunction with gravity supply tanks, or hydropneumatic systems may be used. Flow control valves for individual fixtures under varying pressure conditions automatically adjust flow at the fixture to a predetermined quantity. These valves allow the designer to (1) limit flow at the individual outlet to the minimum suitable for the purpose, (2) hold total demand for the system more closely to the required minimum, and (3) design the piping system as accurately as is practicable for the requirements. Hydronic System Piping The Darcy-Weisbach equation with friction factors from the Moody chart or Colebrook equation (or, alternatively, the HazenWilliams equation) is fundamental to calculating pressure drop in hot- and chilled-water piping; however, charts calculated from these equations (such as Figures 14, 15, and 16) provide easy determination of pressure drops for specific fluids and pipe standards. In addition, tables of pressure drops can be found in Crane Co. (1976) and Hydraulic Institute (1990). The Reynolds numbers represented on the charts in Figures 14, 15, and 16 are all in the turbulent flow regime. For smaller pipes and/ or lower velocities, the Reynolds number may fall into the laminar regime, in which the Colebrook friction factors are no longer valid. Most tables and charts for water are calculated for properties at 15°C. Using these for hot water introduces some error, although the answers are conservative (i.e., cold-water calculations overstate the pressure drop for hot water). Using 15°C water charts for 90°C water should not result in errors in p exceeding 20%. Friction Loss for Water in Commercial Steel Pipe (Schedule 40) Pipe Design 22.27 Licensed for single user. © 2021 ASHRAE, Inc. Fig. 15 Friction Loss for Water in Copper Tubing (Types K, L, M) Fig. 16 Friction Loss for Water in Plastic Pipe (Schedule 80) Table 26 Allowable Number of 25 mm Flush Valves Served by Various Sizes of Water Pipe* Pipe Size, mm 32 40 50 65 75 100 No. of 25 mm Flush Valves 1 2 to 4 5 to 12 13 to 25 26 to 40 41 to 100 *Two 20 mm flush valves are assumed equal to one 25 mm flush valve but can be served by a 25 mm pipe. Water pipe sizing must consider demand factor, available pressure, and length of run. Range of Usage of Pressure Drop Charts General Design Range. The general range of pipe friction loss used for design of hydronic systems is between 100 and 400 Pa per metre of pipe. A value of 250 Pa/m represents the mean to which most systems are designed. Wider ranges may be used in specific designs if certain precautions are taken. Piping Noise. Closed-loop hydronic system piping is generally sized below certain arbitrary upper limits, such as a velocity limit of 1.2 m/s for 50 mm pipe and under, and a pressure drop limit of 400 Pa/m for piping over 50 mm in diameter. Velocities in excess of 1.2 m/s can be used in piping of larger size. This limitation is generally accepted, although it is based on relatively inconclusive experience with noise in piping. Water velocity noise is not caused by water but by free air, sharp pressure drops, turbulence, or a combination of these, that cause cavitation or flashing of water into steam. Therefore, higher velocities may be used if proper precautions are taken to eliminate air and turbulence. Air Separation Air in hydronic systems is usually undesirable because it causes flow noise, allows oxygen to react with piping materials, and sometimes even prevents flow in parts of a system. Air may enter a system at an air/water interface in an open system or in an expansion tank in a closed system, or it may be brought in dissolved in makeup water. Most hydronic systems use air separation devices to remove air. The solubility of air in water increases with pressure and decreases with temperature; thus, separation of air from water is best achieved at the point of lowest pressure and/or highest temperature in a system. For more information, see Chapter 13 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment. 22.28 2021 ASHRAE Handbook—Fundamentals (SI) Table 27 Equivalent Length in Metres of Pipe for 90° Elbows Pipe Size, mm Velocity, m/s 15 20 25 32 40 50 65 90 100 125 150 200 250 300 0.33 0.67 1.00 1.33 1.67 0.4 0.4 0.5 0.5 0.5 0.5 0.6 0.6 0.6 0.7 0.7 0.8 0.8 0.8 0.9 0.9 1.0 1.1 1.1 1.2 1.1 1.2 1.3 1.3 1.4 1.4 1.5 1.6 1.7 1.8 1.6 1.8 1.9 2.0 2.1 2.0 2.3 2.5 2.5 2.6 2.6 2.9 3.1 3.2 3.4 3.2 3.6 3.8 4.0 4.1 3.7 4.2 4.5 4.6 4.8 4.7 5.3 5.6 5.8 6.0 5.7 6.3 6.8 7.1 7.4 6.8 7.6 8.0 8.4 8.8 2.00 2.35 2.67 3.00 3.33 0.5 0.5 0.5 0.5 0.5 0.7 0.7 0.7 0.7 0.8 0.9 0.9 0.9 0.9 0.9 1.2 1.2 1.3 1.3 1.3 1.4 1.5 1.5 1.5 1.5 1.8 1.9 1.9 1.9 1.9 2.2 2.2 2.3 2.3 2.4 2.7 2.8 2.8 2.9 3.0 3.5 3.6 3.6 3.7 3.8 4.3 4.4 4.5 4.5 4.6 5.0 5.1 5.2 5.3 5.4 6.2 6.4 6.5 6.7 6.8 7.6 7.8 8.0 8.1 8.2 9.0 9.2 9.4 9.6 9.8 Table 28 Iron and Copper Elbow Equivalents* Licensed for single user. © 2021 ASHRAE, Inc. Fitting Iron Pipe Copper Tubing Elbow, 90° 45° 90° long-radius 90° welded 1.0 0.7 0.5 0.5 1.0 0.7 0.5 0.5 Reduced coupling Open return bend Angle radiator valve Radiator or convector 0.4 1.0 2.0 3.0 0.4 1.0 3.0 4.0 Boiler or heater Open gate valve Open globe valve 3.0 0.5 12.0 4.0 0.7 17.0 Sources: Giesecke (1926) and Giesecke and Badgett (1931, 1932a). *See Table 10 for equivalent length of one elbow. In the absence of venting, air can be entrained in the water and carried to separation units at flow velocities of 0.5 to 0.6 m/s or more in pipe 50 mm and under. Minimum velocities of 0.6 m/s are therefore recommended. For pipe sizes 50 mm and over, minimum velocities corresponding to a pressure loss of 75 Pa are normally used. Maintaining minimum velocities is particularly important in the upper floors of high-rise buildings where the air tends to come out of solution because of reduced pressures. Higher velocities should be used in downcomer return mains feeding into air separation units located in the basement. Example 5. Determine the iron pipe size for a circuit requiring 1.25 L/s flow. Solution: Enter Figure 4 at 1.25 L/s, read up to pipe size within normal design range (100 to 400 Pa/m), and select 40 mm. Velocity is 1 m/s and pressure loss is 300 Pa/m. Valve and Fitting Pressure Drop Valves and fittings can be listed in elbow equivalents, with an elbow being equivalent to a length of straight pipe. Table 27 lists equivalent lengths of 90° elbows; Table 28 lists elbow equivalents for valves and fittings for iron and copper. Example 6. Determine equivalent length of pipe for a 100 mm open gate valve at a flow velocity of approximately 1.33 m/s. Solution: From Table 27, at 1.33 m/s, each elbow is equivalent to 3.2 m of 100 mm pipe. From Table 28, the gate valve is equivalent to 0.5 elbows. The actual equivalent pipe length (added to measured circuit length for pressure drop determination) will be 3.2 0.5, or 1.6 m of 100 mm. Tee Fitting Pressure Drop. Pressure drop through pipe tees varies with flow through the branch. Figure 17 shows pressure drops for nominal 25 mm tees of equal inlet and outlet sizes and for the flow patterns shown. Idelchik (1986) also presents data for threaded tees. Different investigators present tee loss data in different forms, Fig. 17 Elbow Equivalents of Tees at Various Flow Conditions (Giesecke and Badgett 1931, 1932b) sources. As an estimate of the upper limit to tee losses, a pressure or head loss coefficient of 1.0 may be assumed for entering and leaving 2 /2). flows (i.e., p = 1.0Vin2 /2 + 1.0V out Example 7. Determine the pressure or head losses for a 25 mm (all openings) threaded pipe tee flowing 25% to the side branch, 75% through. The entering flow is 1 L/s (1.79 m/s). Solution: From Figure 17, bottom curve, the number of equivalent elbows for the through-flow is 0.15 elbows; the through-flow is 0.75 L/s (1.34 m/s); and the pressure drop is based on the exit flow rate. Table 27 gives the equivalent length of a 25 mm elbow at 1.33 m/s as 0.8 m. Using Figure 14, the head loss is 900 Pa/m for 25 mm pipe and 0.75 L/s flow. Pipe Design 22.29 p ity, the quieter the system. When condensate must flow against the steam, even in limited quantity, the steam’s velocity must not exceed limits above which the disturbance between the steam and the counterflowing water may (1) produce objectionable sound, such as water hammer, or (2) result in the retention of water in certain parts of the system until the steam flow is reduced sufficiently to allow water to pass. These limits are a function of (1) pipe size; (2) pitch of the pipe if it runs horizontally; (3) quantity of condensate flowing against the steam; and (4) freedom of the piping from water pockets that, under certain conditions, act as a restriction in pipe size. Table 30 lists maximum capacities for various size steam lines. Equivalent Length of Run. All tables for the flow of steam in pipes based on pressure drop must allow for pipe friction, as well as for the resistance of fittings and valves. These resistances are generally stated in terms of straight pipe; that is, a certain fitting produces a drop in pressure equivalent to the stated length of straight run of the same size of pipe. Table 31 gives the length of straight pipe usually allowed for the more common types of fittings and valves. In all pipe sizing tables in this chapter, length of run refers to the equivalent length of run as distinguished from the actual length of pipe. A common sizing method is to assume the length of run and to check this assumption after pipes are sized. For this purpose, length of run is usually assumed to be double the actual length of pipe. = (0.15)(0.8)(900) = 108 Pa = 0.108 kPa pressure drop h = (0.15)(0.8)(900)/(1000)(9.8) = 0.0110 m head loss From Figure 17, top curve, the number of equivalent elbows for the branch flow of 25% is 13 elbows; the branch flow is 0.75 L/s (0.45 m/s); and the head loss or pressure drop is based on the exit flow rate. Table 27 gives the equivalent of a 25 mm elbow at 0.45 m/s as 0.75 m. Using Figure 14, the pressure drop is 130 Pa/m for 25 mm pipe and 0.25 L/s flow. p = (13)(0.75)(130) = 1268 Pa = 1.268 kPa pressure drop h = (13)(0.75)(130)/(1000)(9.8) = 0.129 m head loss 3.3 STEAM PIPING Pressure losses in steam piping for flows of dry or nearly dry steam are governed by Equations (2) to (8) in the section on Design Equations. This section incorporates these principles with other information specific to steam systems. Licensed for single user. © 2021 ASHRAE, Inc. Pipe Sizes Required pipe sizes for a given load in steam heating depend on the following factors: • The initial pressure and the total pressure drop that can be allowed between the source of supply and the end of the return system • The maximum velocity of steam allowable for quiet and dependable operation of the system, taking into consideration the direction of condensate flow • The equivalent length of the run from the boiler or source of steam supply to the farthest heating unit Initial Pressure and Pressure Drop. Table 29 lists pressure drops commonly used with corresponding initial steam pressures for sizing steam piping. Several factors, such as initial pressure and pressure required at the end of the line, should be considered, but it is most important that (1) the total pressure drop does not exceed the initial gage pressure of the system (in practice, it should never exceed one-half the initial gage pressure); (2) pressure drop is not great enough to cause excessive velocities; (3) a constant initial pressure is maintained, except on systems specially designed for varying initial pressures (e.g., subatmospheric pressure), that normally operate under controlled partial vacuums; and (4) for gravity return systems, pressure drop to heating units does not exceed the water column available for removing condensate (i.e., height above the boiler water line of the lowest point on the steam main, on the heating units, or on the dry return). Maximum Velocity. For quiet operation, steam velocity should be 40 to 60 m/s, with a maximum of 75 m/s. The lower the velocTable 30 Example 8. Using Table 31, determine the equivalent length of pipe for the run shown. Measured length = 40 m 100 mm gate valve = 0.6 m Four 100 mm elbows = 10.8 m Table 29 Pressure Drops Used for Sizing Steam Pipea Initial Steam Pressure, kPab Pressure Drop, Pa/m Total Pressure Drop in Steam Supply Piping, kPa Vacuum return 101 108 115 135 170 205 310 445 790 1140 30 to 60 7 30 30 60 115 225 450 450 to 1100 450 to 1100 450 to 2300 7 to 14 0.4 0.4 to 1.7 3.5 10 20 30 35 to 70 70 to 105 105 to 170 170 to 210 a Equipment, control valves, and so forth must be selected based on delivered pressures. b Subtract 101 to convert to pressure above atmospheric. Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions Nominal Pipe Diameter, mm 20 25 32 40 50 Pitch of Pipe, mm/m Capacity Maximum Velocity Capacity Maximum Velocity Capacity Maximum Velocity Capacity Maximum Velocity Capacity Maximum Velocity 20 40 80 120 170 250 350 420 0.4 0.5 0.7 0.8 0.9 1.0 1.2 1.3 2.4 3.4 4.0 4.3 4.9 5.2 6.7 6.7 0.9 1.1 1.5 1.6 1.9 2.2 2.4 2.6 2.7 3.7 4.6 5.2 5.8 6.7 7.3 7.6 1.5 2 2.5 3.1 3.4 3.9 4.2 4.9 3.4 4.3 5.2 6.1 6.7 7.6 7.9 9.4 2.5 3.3 4.2 4.7 5.3 5.9 6.4 7.5 3.7 4.9 5.8 6.7 7.3 7.9 8.5 10.1 5.4 6.8 8.7 10.5 11.7 12.5 12.9 14.5 4.6 5.5 7.3 8.2 9.1 9.8 9.8 10.1 Source: Laschober et al. (1966). Capacity in g/s; velocity in m/s. 22.30 2021 ASHRAE Handbook—Fundamentals (SI) Two 100 mm tees Equivalent On completion of the sizing, the drop could be checked by taking the longest line and actually calculating the equivalent length of run from the pipe sizes determined. If the calculated drop is less than that assumed, the pipe size is adequate; if it is more, an unusual number of fittings is probably involved, and either the lines must be straightened, or the next larger pipe size must be tried. = 11 m = 62.4m Sizing Charts Figure 18 is the basic chart for determining the flow rate and velocity of steam in Schedule 40 pipe for various values of pressure drop per unit length, based on saturated steam at standard pressure (101.325 kPa). Using the multiplier chart (Figure 19), Figure 18 can be used at all saturation pressures between 101 and 1500 kPa (see Example 10). Licensed for single user. © 2021 ASHRAE, Inc. 3.4 High-Pressure Steam Piping Many heating systems for large industrial buildings use highpressure steam [100 to 1000 kPa (gage)]. These systems usually have unit heaters or large built-up fan units with blast heating coils. LOW-PRESSURE STEAM PIPING Values in Table 32 (taken from Figure 18) provide a more rapid means of selecting pipe sizes for the various pressure drops listed and for systems operated at 25 and 85 kPa (gage). The flow rates shown for 25 kPa can be used for saturated pressures from 7 to 41 kPa, and those shown for 85 kPa can be used for saturated pressures from 55 to 110 kPa with an error not exceeding 8%. Both Figure 18 and Table 32 can be used where the flow of condensate does not inhibit the flow of steam. Columns B and C of Table 33 are used in cases where steam and condensate flow in opposite directions, as in risers or runouts that are not dripped. Columns D, E, and F are for one-pipe systems and include risers, radiator valves and vertical connections, and radiator and riser runout sizes, all of which are based on the critical velocity of the steam to allow counterflow of condensate without noise. Return piping can be sized by Table 34, using pipe capacities for wet, dry, and vacuum return lines for several values of pressure drop per metres of equivalent length. Table 31 Nominal Pipe Diameter, mm Example 9. What pressure drop should be used for the steam piping of a system if the measured length of the longest run is 150 m, and the initial pressure must not exceed 14 kPa above atmospheric? Solution: It is assumed, if the measured length of the longest run is 150 m, that when the allowance for fittings is added, the equivalent length of run does not exceed 300 m. Then, with the pressure drop not over one-half of the initial pressure, the drop could be 7 kPa or less. With a pressure drop of 7 kPa and a length of run of 300 m, the drop would be 23 Pa/m; if the total drop were 3.5 kPa, the drop would be 12 Pa/m. In both cases, the pipe could be sized for a desired capacity according to Figure 18. Table 32 Nominal 14 Pa/m Pipe Size, Sat. Press., kPa mm 25 85 Equivalent Length of Fittings to Be Added to Pipe Run Length to Be Added to Run, m Standard Side Elbow Outlet Teeb Gate Valvea Globe Valvea Angle Valvea 15 20 25 32 0.4 0.5 0.7 0.9 0.9 1.2 1.5 1.8 0.1 0.1 0.1 0.2 4 5 7 9 2 3 4 5 40 50 65 80 1.1 1.3 1.5 1.9 2.1 2.4 3.4 4.0 0.2 0.3 0.3 0.4 10 14 16 20 6 7 8 10 100 125 150 2.7 3.3 4.0 5.5 6.7 8.2 0.6 0.7 0.9 28 34 41 14 17 20 200 250 300 350 5.2 6.4 8.2 9.1 11 14 16 19 1.1 1.4 1.7 1.9 55 70 82 94 28 34 40 46 a Valve in full-open position. b Values apply only to a tee used to divert the flow in the main to the last riser. Flow Rate of Steam in Schedule 40 Pipe Pressure Drop, Pa/m 28 Pa/m 58 Pa/m 113 Pa/m 170 Pa/m 225 Pa/m 450 Pa/m Sat. Press., kPa 25 85 Sat. Press., kPa 25 85 Sat. Press., kPa 25 85 Sat. Press., kPa 25 85 Sat. Press., kPa 25 85 Sat. Press., kPa 25 85 20 25 32 40 1.1 2.1 4.5 7.1 1.4 2.6 5.7 8.8 1.8 3.3 6.7 11 2.0 3.9 8.3 13 2.5 4.7 9.8 15 3.0 5.8 12 19 3.7 6.8 14 22 4.4 8.3 17 26 4.5 8.6 18 27 5.4 10 21 33 5.3 10 20 31 6.3 12 25 38 7.6 14 29 45 9.2 17 35 54 50 65 80 90 14 22 40 58 17 27 48 69 20 33 59 84 24 39 69 101 29 48 83 125 36 58 102 153 42 68 121 178 52 83 146 214 53 86 150 219 64 103 180 265 60 98 174 252 74 120 210 305 89 145 246 372 107 173 302 435 100 125 150 200 81 151 242 491 101 180 290 605 120 212 355 702 146 265 422 882 178 307 499 1 020 213 378 611 1 260 249 450 718 1 440 302 536 857 1 800 309 552 882 1 830 378 662 1 080 2 230 363 643 1 060 2 080 436 769 1 260 2 580 529 945 1 500 3 020 617 1 080 1 790 3 720 250 300 907 1 440 1 110 1 730 1 290 2 080 1 590 2 460 1 890 2 950 2 290 3 580 2 650 4 160 3 280 5 040 3 300 5 170 4 030 6 240 3 780 6 050 4 660 7 250 5 380 8 540 6 550 10 200 Notes: 1. Flow rate is in g/s at initial saturation pressures of 25 and 85 kPa (gage). Flow is based on Moody friction factor, where the flow of condensate does not inhibit the flow of steam. 2. The flow rates at 25 kPa cover saturated pressure from 7 to 41 kPa, and the rates at 85 kPa cover saturated pressure from 55 to 110 kPa with an error not exceeding 8%. 3. The steam velocities corresponding to the flow rates given in this table can be found from Figures 18 and 19. 22.31 Licensed for single user. © 2021 ASHRAE, Inc. Pipe Design Notes: Based on Moody Friction Factor where flow of condensate does not inhibit flow of steam. See Figure 19 for obtaining flow rates and velocities of all saturation pressures between 101 to 1500 kPa; see also Examples 9 and 10. Fig. 18 Flow Rate and Velocity of Steam in Schedule 40 Pipe at Saturation Pressure of 101 kPa 22.32 2021 ASHRAE Handbook—Fundamentals (SI) Temperatures are controlled by a modulating or throttling thermostatic valve or by face or bypass dampers controlled by the room air temperature, fan inlet, or fan outlet. Table 33 Steam Pipe Capacities for Low-Pressure Systems Capacity, g/s Two-Pipe System One-Pipe Systems Use of Basic and Velocity Multiplier Charts Condensate Flowing Against Steam Supply Risers Upfeed Radiator Valves and Radiator Vertical and Riser Connections Runouts A Ba Cb Dc E Fb 20 25 32 40 50 1.0 1.8 3.9 6.0 12 0.9 1.8 3.4 5.3 11 0.8 1.4 2.5 4.8 9.1 — 0.9 2.0 2.9 5.3 0.9 0.9 2.0 2.0 2.9 65 80 90 100 125 20 36 49 64 132 17 25 36 54 99 14 25 36 48 — — — — — — 5.3 8.2 15 23 35 150 200 250 300 400 227 472 882 1450 2770 176 378 718 1200 2390 — — — — — — — — — — 69 — — — — Example 10. Given a flow rate of 0.85 kg/s, an initial steam pressure of 800 kPa, and a pressure drop of 2.5 kPa/m, find the size of Schedule 40 pipe required and the velocity of steam in the pipe. Solution: The following steps are shown by the broken line on Figures 18 and 19. 1. Enter Figure 18 at a flow rate of 0.85 kg/s, and move vertically to the horizontal line at 800 kPa 2. Follow along inclined multiplier line (upward and to the left) to horizontal 101 kPa line. The equivalent mass flow at 101 kPa is about 0.30 kg/s. 3. Follow the 0.30 kg/s line vertically until it intersects the horizontal line at 2500 Pa/m pressure drop. Nominal pipe size is 65 mm. The equivalent steam velocity at 101 kPa is about 165 m/s. 4. To find the steam velocity at 800 kPa, locate the value of 165 m/s on the ordinate of the velocity multiplier chart (Figure 19) at 101 kPa. 5. Move along the inclined multiplier line (downward and to the right) until it intersects the vertical 800 kPa pressure line. The velocity is about 65 m/s. Note: Steps 1 through 5 would be rearranged or reversed if different data were given. 3.5 Notes: 1. For one- or two-pipe systems in which condensate flows against steam flow. 2. Steam at average pressure of 7 kPa (gage) used as basis of calculating capacities. STEAM CONDENSATE SYSTEMS The majority of steam systems used in heating applications are two-pipe systems (steam pipe and condensate pipe). This discussion is limited to sizing the condensate lines in two-pipe systems. a Do not use column B for pressure drops of less than 13 Pa per metre of equivalent run. Use Figure 18 or Table 31 instead. b Pitch of horizontal runouts to risers and radiators should be not less than 40 mm/m. Where this pitch cannot be obtained, runouts over 2.5 m in length should be one pipe size larger than that called for in this table. c Do not use column D for pressure drops of less than 9 Pa per metre of equivalent run, except on sizes 80 mm and over. Use Figure 18 or Table 31 instead. Two-Pipe Systems When steam is used for heating a liquid to 102°C or less (e.g., in domestic water heat exchangers, domestic heating water converters, Return Main Table 34 Return Main and Riser Capacities for Low-Pressure Systems, g/s Riser Licensed for single user. © 2021 ASHRAE, Inc. Nominal Pipe Size, mm Vertical Horizontal Pipe Size, mm 7 Pa/m 9 Pa/m 14 Pa/m 28 Pa/m 57 Pa/m 113 Pa/m Wet Dry Vac. Wet Dry Vac. Wet Dry Vac. Wet Dry Vac. Wet Dry Vac. Wet Dry Vac. G H I J K L M N O P Q R S T U V W X Y 20 25 32 40 50 — 16 27 43 88 — 8 16 26 59 — — — — — — 18 31 50 102 — 9 19 30 67 5 18 31 49 103 — 22 38 60 126 — 10 21 33 72 13 22 38 60 126 — 32 54 85 176 — 13 27 43 93 18 31 54 85 179 — 44 76 120 252 — 14 30 48 104 25 44 76 120 252 — — — — — — — — — — 36 62 107 169 357 65 80 90 100 125 150 149 237 347 489 — — 96 184 248 369 — — — — — — — — 199 268 416 577 — — 109 197 277 422 — — 171 275 410 567 993 1590 212 338 504 693 — — 120 221 315 473 — — 212 338 504 693 1220 1950 296 473 693 977 — — 155 284 407 609 — — 300 479 716 984 1730 2770 422 674 1010 1390 — — 171 315 451 678 — — 422 674 1010 1390 2440 3910 — — — — — — — — — — — — 596 953 1424 1953 3440 5519 20 25 32 40 50 — — — — — 6 14 31 47 95 — — — — — — — — — — 6 14 31 47 95 18 31 49 103 171 — — — — — 6 14 31 47 95 22 38 60 126 212 — — — — — 6 14 31 47 95 31 54 85 179 300 — — — — — 6 14 31 47 95 44 76 120 252 422 — — — — — — — — — — 62 107 169 357 596 65 80 90 100 125 — — — — — — — — — — — — — — — — — — — — — — — — — 275 410 564 993 1590 — — — — — — — — — — 338 504 693 1220 1950 — — — — — — — — — — 479 716 984 1730 2772 — — — — — — — — — — 674 1010 1390 2440 3910 — — — — — — — — — — 953 1424 1953 3440 5519 Licensed for single user. © 2021 ASHRAE, Inc. Pipe Design Fig. 19 22.33 Velocity Multiplier Chart for Figure 18 or air-heating coils), the devices are usually provided with a steam control valve. As the control valve throttles, the absolute pressure in the load device decreases, removing all pressure motivation for flow in the condensate return system. To ensure the flow of steam condensate from the load device through the trap and into the return system, it is necessary to provide a vacuum breaker on the device ahead of the trap. This ensures a minimum pressure at the trap inlet of atmospheric pressure plus whatever liquid leg the designer has provided. Then, to ensure flow through the trap, it is necessary to design the condensate system so that it will never have a pressure above atmospheric in the condensate return line. Vented (Open) Return Systems. To achieve this pressure requirement, the condensate return line is usually vented to the atmosphere (1) near the point of entrance of the flow streams from the load traps, (2) in proximity to all connections from drip traps, and (3) at transfer pumps or feedwater receivers. The dry return lines in a vented return system have flowing liquid in the bottom of the line and gas or vapor in the top (Figure 20A). The liquid is the condensate, and the gas may be steam, air, or a mixture of the two. The flow phenomenon for these dry return systems is open channel flow, which is best described by the Manning equation: 23 12 1.00Ar S Q = -----------------------------------n (22) Fig. 20 Types of Condensate Return Systems where Q = volumetric flow rate, m3/s A = cross-sectional area of conduit, m2 r = hydraulic radius of conduit, m n = coefficient of roughness (usually 0.012) S = slope of conduit, m/m Table 35 is a solution to Equation (22) that shows pipe size capacities for steel pipes with various pitches. Recommended practice is to size vertical lines by the maximum pitch shown, although they would actually have a capacity far in excess of that shown. As pitch increases, hydraulic jump that could fill the pipe and other transient effects that could cause water hammer should be avoided. Flow values in Table 35 are calculated for Schedule 40 steel pipe, with a factor of safety of 3.0, and can be used for copper pipes of the same nominal pipe size. The flow characteristics of wet return lines (Figure 20B) are best described by the Darcy-Weisbach equation [Equation (1)]. The motivation for flow is the fluid pressure difference between the entering section of the flooded line and the leaving section. It is common practice, in addition to providing for the fluid pressure 22.34 2021 ASHRAE Handbook—Fundamentals (SI) described for closed returns, and in accordance with Table 34 or Table 37, as applicable. Passage of fluid through the steam trap is a throttling or constantenthalpy process. The resulting fluid on the downstream side of the trap can be a mixture of saturated liquid and vapor. Thus, in nonvented returns, it is important to understand the fluid’s condition when it enters the return line from the trap. The condition of the condensate downstream of the trap can be expressed by the quality x, defined as Licensed for single user. © 2021 ASHRAE, Inc. differential, to slope the return in the direction of flow to a collection point such as a dirt leg to clear the line of sediment or solids. Table 36 is a solution to Equation (1) that shows pipe size capacity for steel pipes with various available fluid pressures. Table 36 can also be used for copper tubing of equal nominal pipe size. Nonvented (Closed) Return Systems. For systems with a continual steam pressure difference between the point where the condensate enters the line and the point where it leaves (Figure 20C), Table 34 or Table 35, as applicable, can be used for sizing the condensate lines. Although these tables express condensate capacity without slope, common practice is to slope the lines in the direction of flow to a collection point (similar to wet returns) to clear the lines of sediment or solids. When saturated condensate at pressures above the return system pressure enters the return (condensate) mains, some of the liquid flashes to steam. This occurs typically at drip traps into a vented return system or at load traps leaving process load devices that are not valve controlled and typically have no subcooling. If the return main is vented, the vent lines relieve any excessive pressure and prevent a backpressure phenomenon that could restrict flow through traps from valved loads; the pipe sizing would be as described for vented dry returns. If the return line is not vented, flash steam causes a pressure rise at that point and the piping could be sized as mv x = -----------------ml + mv where mv = mass of saturated vapor in condensate ml = mass of saturated liquid in condensate Likewise, the volume fraction Vc of the vapor in the condensate is expressed as Vv Vc = ---------------Vl + Vv Vv = volume of saturated vapor in condensate Vl = volume of saturated liquid in condensate The quality and the volume fraction of the condensate downstream of the trap can also be estimated from Equations (25) and (26), respectively. Condensate Flow, g/sa,b 0.5% 1% 2% 4% 15 5 7 10 13 20 10 14 20 29 25 19 27 39 54 Condensate Line Slope 32 40 57 80 113 40 60 85 121 171 50 117 166 235 332 65 189 267 377 534 80 337 476 674 953 100 695 983 1390 1970 125 1270 1800 2540 3590 150 2070 2930 4150 5860 (24) where Table 35 Vented Dry Condensate Return for Gravity Flow Based on Manning Equation Nominal Diameter, mm (23) h1 – hf 2 x = ------------------hg – hf 2 (25) 2 xvg 2 Vc = --------------------------------------vf 1 – x + xvg 2 (26) 2 where h1 = enthalpy of liquid condensate entering trap evaluated at supply pressure for saturated condensate or at saturation pressure corresponding to temperature of subcooled liquid condensate hf2 = enthalpy of saturated liquid at return or downstream pressure of trap hg2 = enthalpy of saturated vapor at return or downstream pressure of trap vf2 = specific volume of saturated liquid at return or downstream pressure of trap vg2 = specific volume of saturated vapor at return or downstream pressure of trap. a Flow is in g/s of 82°C water for Schedule 40 steel pipes. b Flow was calculated from Equation (22) and rounded. Table 36 Vented Wet Condensate Return for Gravity Flow Based on Darcy-Weisbach Equation Condensate Flow, g/sa,b Nominal Diameter, mm 50 100 150 200 250 300 350 400 15 20 25 32 40 50 65 80 100 125 150 13 28 54 114 172 334 536 954 1 960 3 560 5 770 19 41 79 165 248 482 773 1 370 2 810 5 100 8 270 24 51 98 204 308 597 956 1 700 3 470 6 290 10 200 28 60 114 238 358 694 1 110 1 970 4 030 7 290 11 800 32 68 129 267 402 779 1 250 2 210 4 520 8 180 13 200 35 74 142 294 442 857 1 370 2 430 4 960 8 980 14 500 38 81 154 318 479 928 1 480 2 630 5 370 9 720 15 700 41 87 165 341 513 994 1 590 2 810 5 750 10 400 16 800 Condensate Pressure, Pa/m a Flow is in g/s of 82°C water for Schedule 40 steel pipes. b Flow calculated from Equation (1) and rounded. Pipe Design Table 38 22.35 Supply Pressure, kPa (gage) Return Pressure, kPa (gage) x, Fraction Vapor, Mass Basis Vc , Fraction Vapor, Volume Basis 35 103 207 345 690 1030 690 1030 0 0 0 0 0 0 103 103 0.016 0.040 0.065 0.090 0.133 0.164 0.096 0.128 0.962 0.985 0.991 0.994 0.996 0.997 0.989 0.992 Table 39 One-Pipe Systems Gravity one-pipe air vent systems in which steam and condensate flow in the same pipe, frequently in opposite directions, are considered obsolete and are no longer being installed. Chapter 33 of the 1993 ASHRAE Handbook—Fundamentals or earlier ASHRAE Handbook volumes include descriptions of and design information for one-pipe systems. Estimated Return Line Pressures Pressure in Return Line, Pa (gage) Pressure Drop, Pa/m 200 kPa (gage) Supply 1000 kPa (gage) Supply 30 60 120 180 240 480 3.5 7 14 21 28 — 9 18 35 52 70 138 Licensed for single user. © 2021 ASHRAE, Inc. Table 38 presents some values for quality and volume fraction for typical supply and return pressures in heating and ventilating systems. Note that the percent of vapor on a mass basis x is small, although the percent of vapor on a volume basis Vc is very large. This indicates that the return pipe cross section is predominantly occupied by vapor. Figure 21 is a working chart to determine the quality of condensate entering the return line from the trap for various combinations of supply and return pressures. If the liquid is subcooled entering the trap, the saturation pressure corresponding to the liquid temperature should be used for the supply or upstream pressure. Typical pressures in the return line are given in Table 39. Flash Steam from Steam Trap on Pressure Drop 3.6 GAS PIPING Piping for gas appliances should be of adequate size and installed so that it provides a supply of gas sufficient to meet the maximum demand without undue loss of pressure between the point of supply (the meter) and the appliance. The size of gas pipe required depends on (1) maximum gas consumption to be provided, (2) length of pipe and number of fittings, (3) allowable pressure loss from the outlet of the meter to the appliance, and (4) density of the gas. Insufficient gas flow from excessive pressure losses in gas supply lines can cause inefficient operation of gas-fired appliances and sometimes create hazardous operations. Gas-fired appliances are normally equipped with a data plate giving information on maximum gas flow requirements or input as well as inlet gas pressure requirements. The local gas utility can give the gas pressure available at the utility’s gas meter. Using this information, the required size of gas piping can be calculated for satisfactory operation of the appliance(s). Table 40 gives pipe capacities for gas flow for up to 60 m of pipe based on a gas density of 0.735 kg/m3. Capacities for pressures less than 10 kPa may also be determined by the following equation from NFPA/IAS National Fuel Gas Code (NFPA Standard 54/ANSI Standard Z223.1): Q = 0.0001d 2.623(p/CL)0.541 Fig. 21 Working Chart for Determining Percentage of Flash Steam (Quality) Table 40 Nominal Iron Internal Pipe Size, Diameter, mm mm 8 10 15 20 25 32 40 50 65 80 100 9.25 12.52 15.80 20.93 26.14 35.05 40.89 52.50 62.71 77.93 102.26 (27) where Q = flow rate at 15°C and 101 kPa, L/s Maximum Capacity of Gas Pipe in Litres per Second Length of Pipe, m 5 10 15 20 25 30 35 40 45 50 55 60 0.19 0.43 0.79 1.65 2.95 6.4 9.6 18.4 29.3 51.9 105.8 0.13 0.29 0.54 1.13 2.03 4.4 6.6 12.7 20.2 35.7 72.7 0.11 0.24 0.44 0.91 1.63 3.5 5.3 10.2 16.2 28.6 58.4 0.09 0.20 0.37 0.78 1.40 3.0 4.5 8.7 13.9 24.5 50.0 0.08 0.18 0.33 0.69 1.24 2.7 4.0 7.7 12.3 21.7 44.3 0.07 0.16 0.30 0.63 1.12 2.4 3.6 7.0 11.1 19.7 40.1 0.07 0.15 0.28 0.58 1.03 2.2 3.3 6.4 10.2 18.1 36.9 0.06 0.14 0.26 0.54 0.96 2.1 3.1 6.0 9.5 16.8 34.4 0.06 0.13 0.24 0.50 0.90 1.9 2.9 5.6 8.9 15.8 32.2 0.06 0.12 0.23 0.47 0.85 1.8 2.8 5.3 8.4 14.9 30.4 0.05 0.12 0.22 0.45 0.81 1.7 2.6 5.0 8.0 14.2 28.9 0.05 0.11 0.21 0.43 0.77 1.7 2.5 4.8 7.7 13.5 27.6 Note: Capacity is in litres per second at gas pressures of 3.5 kPa (gage) or less and pressure drop of 75 kPa; density = 0.735 kg/m3. Copyright by American Gas Association and National Fire Protection Association. Used by permission of copyright holders. 22.36 2021 ASHRAE Handbook—Fundamentals (SI) Licensed for single user. © 2021 ASHRAE, Inc. Fig. 22 Typical Oil Circulating Loop d = inside diameter of pipe, mm p = pressure drop, Pa C = factor for viscosity, density, and temperature = 0.00223(t + 273)s0.8480.152 t = temperature, °C s = ratio of density of gas to density of air at 15°C and 101 kPa = viscosity of gas, Pa·s (12 for natural gas, 8 for propane) L = pipe length, m Gas service in buildings is generally delivered in the lowpressure range of 1.7 kPa (gage). The maximum pressure drop allowable in piping systems at this pressure is generally 125 Pa but is subject to regulation by local building, plumbing, and gas appliance codes [see also the NFPA/IAS National Fuel Gas Code (NFPA Standard 54/ANSI Standard Z223.1)]. Where large quantities of gas are required or where long lengths of pipe are used (e.g., in industrial buildings), low-pressure limitations result in large pipe sizes. Local codes may allow (and local gas companies may deliver) gas at higher pressures [e.g., 15, 35, or 70 kPa (gage)]. Under these conditions, an allowable pressure drop of 10% of the initial pressure is used, and pipe sizes can be reduced significantly. Gas pressure regulators at the appliance must be specified to accommodate higher inlet pressures. NFPA/IAS (2012) provides information on pipe sizing for various inlet pressures and pressure drops at higher pressures. More complete information on gas piping can be found in the Gas Engineers’ Handbook (1970). 3.7 FUEL OIL PIPING The pipe used to convey fuel oil to oil-fired appliances must be large enough to maintain low pump suction pressure and, in the case of circulating loop systems, to prevent overpressure at the burner oil pump inlet. Pipe materials must be compatible with the fuel and must be carefully assembled to eliminate all leaks. Leaks in suction lines can cause pumping problems that result in unreliable burner operation. Leaks in pressurized lines create fire hazards. Cast-iron or aluminum fittings and pipe are unacceptable. Pipe joint compounds must be selected carefully. Oil pump suction lines should be sized so that at maximum suction line flow conditions, the maximum vacuum will not exceed 34 kPa for distillate grade fuels and 50 kPa for residual oils. Oil supply lines to burner oil pumps should not be pressurized by circulating loop systems or aboveground oil storage tanks to more than Table 41 Recommended Nominal Size for Fuel Oil Suction Lines from Tank to Pump (Residual Grades No. 5 and No. 6) Pumping Rate, L/h 10 50 100 200 300 400 500 600 700 800 40 40 40 50 50 50 65 65 65 Length of Run in Metres at Maximum Suction Lift of 4.5 kPa 20 30 40 50 60 70 80 90 100 40 40 50 50 50 65 65 65 65 40 50 50 65 65 65 65 65 80 50 50 50 65 65 65 80 80 80 50 65 65 65 80 80 80 80 100 50 65 65 65 80 65 65 65 80 80 65 65 80 80 80 80 80 80 80 80 80 80 80 80 100 80 80 80 100 100 80 100 100 100 100 100 100 100 100 100 100 100 100 100 100 Notes: 1. Sizes (in millimetres) are nominal. 2. Pipe sizes smaller than 25 mm ISO are not recommended for use with residual grade fuel oils. 3. Lines conveying fuel oil from pump discharge port to burners and tank return may be reduced by one or two sizes, depending on piping length and pressure losses. 34 kPa, or pump shaft seals may fail. A typical oil circulating loop system is shown in Figure 22. In assembling long fuel pipe lines, be careful to avoid air pockets. On overhead circulating loops, the line should vent air at all high points. Oil supply loops for one or more burners should be the continuous circulation type, with excess fuel returned to the storage tank. Dead-ended pressurized loops can be used, but air or vapor venting is more problematic. Where valves are used, select ball or gate valves. Globe valves are not recommended because of their high pressure drop characteristics. Oil lines should be tested after installation, particularly if they are buried, enclosed, or otherwise inaccessible. Failure to perform this test is a frequent cause of later operating difficulties. A suction line can be hydrostatically tested at 1.5 times its maximum operating pressure or at a vacuum of not less than 70 kPa. Pressure or vacuum tests should continue for at least 60 min. If there is no noticeable drop in the initial test pressure, the lines can be considered tight. Pipe Sizes for Heavy Oil Tables 41 and 42 give recommended pipe sizes for handling No. 5 and No. 6 oils (residual grades) and No. 1 and No. 2 oils (distillate Pipe Design 22.37 Table 42 Recommended Nominal Size for Fuel Oil Suction Lines from Tank to Pump (Distillate Grades No. 1 and No. 2) Pumping Rate, L/h 10 50 100 200 300 400 500 600 700 800 15 15 15 15 20 20 20 20 20 Length of Run in Metres at Maximum Suction Lift of 9.0 kPa 20 30 40 50 60 70 80 90 100 15 15 20 20 20 25 25 25 25 25 25 25 32 32 32 50 50 50 15 15 20 20 20 25 25 25 25 15 15 20 20 20 25 25 25 25 15 20 20 20 25 25 25 25 32 20 20 20 25 25 25 32 32 32 20 20 25 25 25 32 32 32 32 20 20 25 25 25 32 32 32 32 25 25 25 25 32 32 32 50 50 Licensed for single user. © 2021 ASHRAE, Inc. Note: Sizes (in millimetres) are nominal. grades), respectively. Storage tanks and piping and pumping facilities for delivering the oil from the tank to the burner are important considerations in the design of an industrial oil-burning system. The construction and location of the tank and oil piping are usually subject to local regulations and National Fire Protection Association (NFPA) Standards 30 and 31. REFERENCES ASHRAE members can access ASHRAE Journal articles and ASHRAE research project final reports at technologyportal.ashrae .org. Articles and reports are also available for purchase by nonmembers in the online ASHRAE Bookstore at www.ashrae.org/bookstore. ASHRAE. 2013. Safety standard for refrigeration systems. ANSI/ASHRAE Standard 15-2013. ASHRAE. 2013. Energy standard for buildings except low-ride residential buildings. ANSI/ASHRAE/IES Standard 90.1-2013. ASME. 2013. Pipe threads, general purpose, inch. Standard B1.20.1-2013. American Society of Mechanical Engineers, New York. ASME. 2006. Pipe threads, 60 deg. general purpose (metric). Standard B1.20.2M-2006. American Society of Mechanical Engineers, New York. ASME. 2015. Gray iron pipe flanges and flanged fittings: Classes 25, 125, and 250. Standard B16.1-2015. American Society of Mechanical Engineers, New York. ASME. 2011. Malleable iron threaded fittings: Classes 150 and 300. Standard B16.3-2011. American Society of Mechanical Engineers, New York. ASME. 2011. Gray iron threaded fittings: Classes 125 and 250. Standard B16.4-2011. American Society of Mechanical Engineers, New York. ASME. 2009. Pipe flanges and flanged fittings: NPS 1/2 through NPS 24 metric/inch standard. Standard B16.5-2009. American Society of Mechanical Engineers, New York. ASME. 2012. Factory made wrought buttwelding fittings. Standard B16.92012. American Society of Mechanical Engineers, New York. ASME. 2009. Forged fittings, socket-welding and threaded. Standard B16.11-2009. American Society of Mechanical Engineers, New York. ASME. 2009. Cast iron threaded drainage fittings. Standard B16.12-2009. American Society of Mechanical Engineers, New York. ASME. 2013. Cast copper alloy threaded fittings: Classes 125 and 250. Standard B16.15-2013. American Society of Mechanical Engineers, New York. ASME. 2012. Cast copper alloy solder joint pressure fittings. Standard B16.18-2012. American Society of Mechanical Engineers, New York. ASME. 2013. Wrought copper and copper alloy solder-joint pressure fittings. Standard B16.22-2013. American Society of Mechanical Engineers, New York. ASME. 2011. Cast copper alloy solder joint drainage fittings: DWV. Standard B16.23-2011. American Society of Mechanical Engineers, New York. ASME. 2011. Cast copper alloy pipe flanges and flanged fittings: Classes 150, 300, 600, 900, 1500, and 2500. Standard B16.24-2011. American Society of Mechanical Engineers, New York. ASME. 2011. Cast copper alloy fittings for flared copper tubes. Standard B16.26-2011. American Society of Mechanical Engineers, New York. ASME. 2012. Wrought copper and wrought copper alloy solder-joint drainage fittings—DWV. Standard B16.29-2012. American Society of Mechanical Engineers, New York. ASME. 2011. Ductile iron pipe flanges and flanged fittings: Classes 150 and 300. Standard B16.42-2011. American Society of Mechanical Engineers, New York. ASME. 2016. Power piping. Standard B31.1-2016. American Society of Mechanical Engineers, New York. ASME. 2016. Refrigeration piping and heat transfer components. Standard B31.5-2016. American Society of Mechanical Engineers, New York. ASME. 2014. Building services piping. Standard B31.9-2014. American Society of Mechanical Engineers, New York. ASME. 2015. Welded and seamless wrought steel pipe. Standard B36.10M2015. American Society of Mechanical Engineers, New York. ASME. 2015. Qualification standard for welding and brazing procedures, welders, brazers, and welding and brazing operators. Boiler and Pressure Vessel Code, Section IX. American Society of Mechanical Engineers, New York. ASTM. 2012. Standard specification for pipe, steel, black and hot-dipped, zinc-coated, welded, and seamless. Standard A53. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for seamless carbon steel pipe for hightemperature service. Standard A106. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2014. Standard specification for seamless copper water tube. Standard B88. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2016. Standard specification for seamless copper tube for air conditioning and refrigeration field service. Standard B280. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2011. Standard specification for rigid poly(vinyl chloride) (PVC) compounds and chlorinated poly(vinyl chloride) (CPVC) compounds. Standard D1784. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for poly(vinyl chloride) (PVC) plastic pipe, schedules 40, 80, and 120. Standard D1785. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard test method for determining dimensions of thermoplastic pipe and fittings. Standard D2122. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2012. Standard specification for polyethylene (PE) plastic pipe (SIDR-PR) based on controlled inside diameter. Standard D2239. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for threaded poly(vinyl chloride) (PVC) plastic pipe fittings, schedule 80. Standard D2464. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for poly(vinyl chloride) (PVC) plastic pipe fittings, schedule 40. Standard D2466. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for poly(vinyl chloride) (PVC) plastic pipe fittings, schedule 80. Standard D2467. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2012. Standard specification for solvent cements for poly(vinyl chloride) (PVC) plastic piping systems. Standard D2564. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2014. Standard specification for acrylonitrile-butadiene-styrene (ABS) schedule 40 plastic drain, waste, and vent pipe and fittings. Standard D2661. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2014. Standard specification for poly(vinyl chloride) (PVC) plastic drain, waste, and vent pipe and fittings. Standard D2665. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2013. Standard test method for obtaining hydrostatic design basis for thermoplastic pipe materials or pressure design basis for thermoplastic pipe products. Standard D2837-13e1. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2012. Standard practice for obtaining hydrostatic or pressure design basis for “fiberglass” (glass-fiber-reinforced thermosetting-resin) pipe and fittings. Standard D2992. American Society for Testing and Materials, West Conshohocken, PA. Licensed for single user. © 2021 ASHRAE, Inc. 22.38 ASTM. 2014. Standard specification for polyethylene plastics pipe and fittings materials. Standard D3350. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2016. Standard classification system and basis for specifications for rigid acrylonitrile-butadiene-styrene (ABS) materials for pipe and fittings. Standard D3965. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. Standard specification for threaded chlorinated poly(vinyl chloride) (CPVC) plastic pipe fittings, schedule 80. Standard F437. American Society for Testing and Materials, West Conshohocken, PA. ASTM. 2015. 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