There are other systems, however, where the required inlet pressure to the different appliances may be quite varied. In such cases, the greatest inlet pressure required must be satisfied, as well as the farthest appliance, which is almost always the critical appliance in small systems.
There is an additional requirement to be observed besides the capacity of the system at 100-percent flow. That requirement is that at minimum flow, the pressure at the inlet to any appliance does not exceed the pressure rating of the appliance regulator. This would seldom be of concern in small systems if the source pressure is 1/2 psi (14-inch w.c.) (3.5 kPa) or less but it should be verified for systems with greater gas pressure at the point of supply.
To determine the size of piping used in a gas piping system, the following factors must be considered:
For any gas piping system, or special appliance, or for conditions other than those covered by the tables provided in this code, such as longer runs, greater gas demands or greater pressure drops, the size of each gas piping system should be determined by standard engineering practices acceptable to the code official.
TABLE A.2.2
EQUIVALENT LENGTHS OF PIPE FITTINGS AND VALVES
SCREWED FITTINGS1 | 90° WELDING ELBOWS AND SMOOTH BENDS2 | ||||||||||
45°/Ell | 90°/Ell | 180°close return bends | Tee | R/d = 1 | R/d = 11/3 | R/d = 2 | R/d = 4 | R/d = 6 | R/d = 8 | ||
k factor = | 0.42 | 0.90 | 2.00 | 1.80 | 0.48 | 0.36 | 0.27 | 0.21 | 0.27 | 0.36 | |
L/d' ratio4 n = | 1 4 | 30 | 67 | 60 | 16 | 12 | 9 | 7 | 9 | 12 | |
Nominal pipe size, inches | Inside diameter d, inches, Schedule 406 | L = Equivalent Length In Feet of Schedule 40 (Standard-weight) Straight Pipe6 | |||||||||
1/2 | 0.622 | 0.73 | 1.55 | 3.47 | 3.10 | 0.83 | 0.62 | 0.47 | 0.36 | 0.47 | 0.62 |
3/4 | 0.824 | 0.96 | 2.06 | 4.60 | 4.12 | 1.10 | 0.82 | 0.62 | 0.48 | 0.62 | 0.82 |
1 | 1.049 | 1.22 | 2.62 | 5.82 | 5.24 | 1.40 | 1.05 | 0.79 | 0.61 | 0.79 | 1.05 |
11/4 | 1.380 | 1.61 | 3.45 | 7.66 | 6.90 | 1.84 | 1.38 | 1.03 | 0.81 | 1.03 | 1.38 |
11/2 | 1.610 | 1.88 | 4.02 | 8.95 | 8.04 | 2.14 | 1.61 | 1.21 | 0.94 | 1.21 | 1.61 |
2 | 2.067 | 2.41 | 5.17 | 11.5 | 10.3 | 2.76 | 2.07 | 1.55 | 1.21 | 1.55 | 2.07 |
21/2 | 2.469 | 2.88 | 6.16 | 13.7 | 12.3 | 3.29 | 2.47 | 1.85 | 1.44 | 1.85 | 2.47 |
3 | 3.068 | 3.58 | 7.67 | 17.1 | 15.3 | 4.09 | 3.07 | 2.30 | 1.79 | 2.30 | 3.07 |
4 | 4.026 | 4.70 | 10.1 | 22.4 | 20.2 | 5.37 | 4.03 | 3.02 | 2.35 | 3.02 | 4.03 |
5 | 5.047 | 5.88 | 12.6 | 28.0 | 25.2 | 6.72 | 5.05 | 3.78 | 2.94 | 3.78 | 5.05 |
6 | 6.065 | 7.07 | 15.2 | 33.8 | 30.4 | 8.09 | 6.07 | 4.55 | 3.54 | 4.55 | 6.07 |
8 | 7.981 | 9.31 | 20.0 | 44.6 | 40.0 | 10.6 | 7.98 | 5.98 | 4.65 | 5.98 | 7.98 |
10 | 10.02 | 11.7 | 25.0 | 55.7 | 50.0 | 13.3 | 10.0 | 7.51 | 5.85 | 7.51 | 10.0 |
12 | 11.94 | 13.9 | 29.8 | 66.3 | 59.6 | 15.9 | 11.9 | 8.95 | 6.96 | 8.95 | 11.9 |
14 | 13.13 | 15.3 | 32.8 | 73.0 | 65.6 | 17.5 | 13.1 | 9.85 | 7.65 | 9.85 | 13.1 |
16 | 15.00 | 17.5 | 37.5 | 83.5 | 75.0 | 20.0 | 15.0 | 11.2 | 8.75 | 11.2 | 15.0 |
18 | 16.88 | 19.7 | 42.1 | 93.8 | 84.2 | 22.5 | 16.9 | 12.7 | 9.85 | 12.7 | 16.9 |
20 | 18.81 | 22.0 | 47.0 | 105.0 | 94.0 | 25.1 | 18.8 | 14.1 | 11.0 | 14.1 | 18.8 |
24 | 22.63 | 26.4 | 56.6 | 126.0 | 113.0 | 30.2 | 22.6 | 17.0 | 13.2 | 17.0 | 22.6 |
(continued)
TABLE A.2.2—continued
EQUIVALENT LENGTHS OF PIPE FITTINGS AND VALVES
MITER ELBOWS3 (No. of miters) | WELDING TEES | VALVES (screwed, flanged, or welded) | ||||||||||
1-45° | 1-60° | 1-90° | 2-90°5 | 3-90°5 | Forged | Miter3 | Gate | Globe | Angle | Swing Check | ||
k factor = | 0.45 | 0.90 | 1.80 | 0.60 | 0.45 | 1.35 | 1.80 | 0.21 | 10 | 5.0 | 2.5 | |
L/d' ratio4 n = | 15 | 30 | 60 | 20 | 15 | 45 | 60 | 7 | 333 | 167 | 83 | |
Nominal pipe size, inches | Inside diameter d, inches, Schedule 406 | L = Equivalent Length In Feet of Schedule 40 (Standard-weight) Straight Pipe6 | ||||||||||
1/2 | 0.622 | 0.78 | 1.55 | 3.10 | 1.04 | 0.78 | 2.33 | 3.10 | 0.36 | 17.3 | 8.65 | 4.32 |
3/4 | 0.824 | 1.03 | 2.06 | 4.12 | 1.37 | 1.03 | 3.09 | 4.12 | 0.48 | 22.9 | 11.4 | 5.72 |
1 | 1.049 | 1.31 | 2.62 | 5.24 | 1.75 | 1.31 | 3.93 | 5.24 | 0.61 | 29.1 | 14.6 | 7.27 |
11/4 | 1.380 | 1.72 | 3.45 | 6.90 | 2.30 | 1.72 | 5.17 | 6.90 | 0.81 | 38.3 | 19.1 | 9.58 |
11/2 | 1.610 | 2.01 | 4.02 | 8.04 | 2.68 | 2.01 | 6.04 | 8.04 | 0.94 | 44.7 | 22.4 | 11.2 |
2 | 2.067 | 2.58 | 5.17 | 10.3 | 3.45 | 2.58 | 7.75 | 10.3 | 1.21 | 57.4 | 28.7 | 14.4 |
21/2 | 2.469 | 3.08 | 6.16 | 12.3 | 4.11 | 3.08 | 9.25 | 12.3 | 1.44 | 68.5 | 34.3 | 17.1 |
3 | 3.068 | 3.84 | 7.67 | 15.3 | 5.11 | 3.84 | 11.5 | 15.3 | 1.79 | 85.2 | 42.6 | 21.3 |
4 | 4.026 | 5.04 | 10.1 | 20.2 | 6.71 | 5.04 | 15.1 | 20.2 | 2.35 | 112.0 | 56.0 | 28.0 |
5 | 5.047 | 6.30 | 12.6 | 25.2 | 8.40 | 6.30 | 18.9 | 25.2 | 2.94 | 140.0 | 70.0 | 35.0 |
6 | 6.065 | 7.58 | 15.2 | 30.4 | 10.1 | 7.58 | 22.8 | 30.4 | 3.54 | 168.0 | 84.1 | 42.1 |
8 | 7.981 | 9.97 | 20.0 | 40.0 | 13.3 | 9.97 | 29.9 | 40.0 | 4.65 | 22.0 | 111.0 | 55.5 |
10 | 10.02 | 12.5 | 25.0 | 50.0 | 16.7 | 12.5 | 37.6 | 50.0 | 5.85 | 278.0 | 139.0 | 69.5 |
12 | 11.94 | 14.9 | 29.8 | 59.6 | 19.9 | 14.9 | 44.8 | 59.6 | 6.96 | 332.0 | 166.0 | 83.0 |
14 | 13.13 | 16.4 | 32.8 | 65.6 | 21.9 | 16.4 | 49.2 | 65.6 | 7.65 | 364.0 | 182.0 | 91.0 |
16 | 15.00 | 18.8 | 37.5 | 75.0 | 25.0 | 18.8 | 56.2 | 75.0 | 8.75 | 417.0 | 208.0 | 104.0 |
18 | 16.88 | 21.1 | 42.1 | 84.2 | 28.1 | 21.1 | 63.2 | 84.2 | 9.85 | 469.0 | 234.0 | 117.0 |
20 | 18.81 | 23.5 | 47.0 | 94.0 | 31.4 | 23.5 | 70.6 | 94.0 | 11.0 | 522.0 | 261.0 | 131.0 |
24 | 22.63 | 28.3 | 56.6 | 113.0 | 37.8 | 28.3 | 85.0 | 113.0 | 13.2 | 629.0 | 314.0 | 157.0 |
TABLE A.2.4
MULTIPLIERS TO BE USED WITH TABLES 402.4(1)
THROUGH 402.4(22) WHERE THE SPECIFIC GRAVITY
OF THE GAS IS OTHER THAN 0.60
SPECIFIC GRAVITY | MULTIPLIER | SPECIFIC GRAVITY | MULTIPLIER |
0.35 | 1.31 | 1.00 | 0.78 |
0.40 | 1.23 | 1.10 | 0.74 |
0.45 | 1.16 | 1.20 | 0.71 |
0.50 | 1.10 | 1.30 | 0.68 |
0.55 | 1.04 | 1.40 | 0.66 |
0.60 | 1.00 | 1.50 | 0.63 |
0.65 | 0.96 | 1.60 | 0.61 |
0.70 | 0.93 | 1.70 | 0.59 |
0.75 | 0.90 | 1.80 | 0.58 |
0.80 | 0.87 | 1.90 | 0.56 |
0.85 | 0.84 | 2.00 | 0.55 |
0.90 | 0.82 | 2.10 | 0.54 |
Desired Value | = |
= | 147 × 1.414 | = | 208 MBH |
(MBH = 1000 Btu/h)
TABLE A.3.4
THOUSANDS OF BTU/H (MBH) OF NATURAL GAS PER 100 FEET OF PIPE AT VARIOUS PRESSURE DROPS AND PIPE DIAMETERS
PRESSURE DROP PER 100 FEET IN INCHES W.C. | PIPE SIZES (inch) | |||||
1/2 | 3/4 | 1 | 11/4 | 11/2 | 2 | |
0.2 | 31 | 64 | 121 | 248 | 372 | 716 |
0.3 | 38 | 79 | 148 | 304 | 455 | 877 |
0.5 | 50 | 104 | 195 | 400 | 600 | 1160 |
1.0 | 71 | 147 | 276 | 566 | 848 | 1640 |
where:
Q | = | Rate, cubic feet per hour at 60°F and 30-inch mercury column |
D | = | Inside diameter of pipe, in. |
P1 | = | Upstream pressure, psia |
P2 | = | Downstream pressure, psia |
Y | = | Superexpansibility factor = 1/supercompressibility factor |
Cr | = | Factor for viscosity, density and temperature* |
Note: See Table 402.4 for Y and Cr for natural gas and propane.
S | = | Specific gravity of gas at 60°F and 30-inch mercury column (0.60 for natural gas, 1.50 for propane), or = 1488μ |
T | = | Absolute temperature, °F or = t + 460 |
t | = | Temperature, °F |
Z | = | Viscosity of gas, centipoise (0.012 for natural gas, 0.008 for propane), or = 1488μ |
ƒba | = | Base friction factor for air at 60°F (CF = 1) |
L | = | Length of pipe, ft |
ΔH | = | Pressure drop, in. w.c. (27.7 in. H2O = 1 psi) |
(For SI, see Section 402.4)
TABLE A.5.1
SCHEDULE 40 STEEL PIPE STANDARD SIZES
NOMINAL SIZE (inch) | INTERNAL DIAMETER (inch) | NOMINAL SIZE (inch) | INTERNAL DIAMETER (inch) |
1/4 | 0.364 | 11/2 | 1.610 |
3/8 | 0.493 | 2 | 2.067 |
1/2 | 0.622 | 21/2 | 2.469 |
3/4 | 0.824 | 3 | 3.068 |
1 | 1.049 | 31/2 | 3.548 |
11/4 | 1.380 | 4 | 4.026 |
TABLE A.5.2
COPPER TUBE STANDARD SIZES
TUBE TYPE | NOMINAL OR STANDARD SIZE (inches) | INTERNAL DIAMETER (inches) |
K | 1/4 | 0.305 |
L | 1/4 | 0.315 |
ACR (D) | 3/8 | 0.315 |
ACR (A) | 3/8 | 0.311 |
K | 3/8 | 0.402 |
L | 3/8 | 0.430 |
ACR (D) | 1/2 | 0.430 |
ACR (A) | 1/2 | 0.436 |
K | 1/2 | 0.527 |
L | 1/2 | 0.545 |
ACR (D) | 5/8 | 0.545 |
ACR (A) | 5/8 | 0.555 |
K | 5/8 | 0.652 |
L | 5/8 | 0.666 |
ACR (D) | 3/4 | 0.666 |
ACR (A) | 3/4 | 0.680 |
K | 3/4 | 0.745 |
L | 3/4 | 0.785 |
ACR | 7/8 | 0.785 |
K | 1 | 0.995 |
L | 1 | 1.025 |
ACR | 11/8 | 1.025 |
K | 11/4 | 1.245 |
L | 11/4 | 1.265 |
ACR | 13/8 | 1.265 |
K | 11/2 | 1.481 |
L | 11/2 | 1.505 |
ACR | 15/8 | 1.505 |
K | 2 | 1.959 |
L | 2 | 1.985 |
ACR | 21/8 | 1.985 |
K | 21/2 | 2.435 |
L | 21/2 | 2.465 |
ACR | 25/8 | 2.465 |
K | 3 | 2.907 |
L | 3 | 2.945 |
ACR | 31/8 | 2.945 |
(4) If a different gravity factor is applied to this example, the values in the row marked 60 feet (18 288 mm) of Table 402.4(2) would be multiplied by the appropriate multiplier from Table A.2.4 and the resulting cubic feet per hour values would be used to size the piping.
FIGURE A.6.1
PIPING PLAN SHOWING A STEEL PIPING SYSTEM
Note: It is not unusual to oversize the supply line by 25 to 50 percent of the as-installed load. EHD size 18 has a capacity of 189 cfh (5.35 m3/ hr).
FIGURE A.6.2
PIPING PLAN SHOWING A CSST SYSTEM
FIGURE A.6.3
PIPING PLAN SHOWING A COPPER TUBING SYSTEM
FIGURE A.6.4
PIPING PLAN SHOWING A MODIFICATION
TO EXISTING PIPING SYSTEM
T1 | = | Initial temperature, absolute (T1 + 459) |
T2 | = | Final temperature, absolute (T2 + 459) |
P1 | = | Initial pressure, psia (P1 + 14.7) |
P2 | = | Final pressure, psia (P2 + 14.7) |
P2 | = | 32.7 - 14.7 |
P2 | = | 18 psig |
Therefore, the gauge could be expected to register 18 psig (124 kPa) when the ambient temperature is 40°F (4°C).
For 1/2-inch pipe, ΔH = 20 feet/100 feet × 0.3 inch w.c. = 0.06 in w.c.
For 3/4-inch pipe, ΔH = 15 feet/100 feet × 0.3 inch w.c. = 0.045 in w.c.
For 1 inch pipe: ΔH = 10 feet/100 feet × 0.2 inch w.c. = 0.02 in w.c.
For 3/4-inch pipe: ΔH = 10 feet/100 feet × [0.5 inch w.c. + (110,000 Btu/hr-104,000 Btu/hr)/(147,000 Btu/hr-104,000 Btu/hr) × (1.0 inches w.c. - 0.5 inch w.c.)] = 0.1 × 0.57 inch w.c. ≈ 0.06 inch w.c.
Note that the pressure drop between 104,000 Btu/hr and 147,000 Btu/hr has been interpolated as 110,000 Btu/hr.
For 1-inch pipe: ΔH = 20 feet/100 feet × [0.2 inch w.c. + (14,000 Btu/hr)/(27,000 Btu/hr) × 0.1 inch w.c.] = 0.05 inch w.c.
For 3/4-inch pipe: ΔH = 20 feet/100 feet × 1.0 inch w.c. = 0.2 inch w.c.
Note that the pressure drop between 121,000 Btu/hr and 148,000 Btu/hr has been interpolated as 135,000 Btu/hr, but interpolation for the 3/4-inch pipe (trivial for 104,000 Btu/hr to 147,000 Btu/hr) was not used.
For 1-inch pipe: ΔH = 30 feet/100 feet × 1.0 inches w.c. = 0.3 inch w.c.
For 11/4-inch pipe: ΔH = 30 feet/100 feet × 0.2 inch w.c. = 0.06 inch w.c.
Note that interpolation for these options is ignored since the table values are close to the 245,000 Btu/hr carried by that section.
Minimum pressure drop to farthest appliance:
ΔH = 0.06 inch w.c. + 0.02 inch w.c. + 0.06 inch w.c. = 0.14 inch w.c.
Larger pressure drop to the farthest appliance:
ΔH = 0.06 inch w.c. + 0.06 inch w.c. + 0.3 inch w.c. = 0.42 inch w.c.
Notice that Section 2 and the run to B do not enter into this calculation, provided that the appliances have similar input pressure requirements.
For SI units: 1 Btu/hr = 0.293 W, 1 cubic foot = 0.028 m3, 1 foot = 0.305 m, 1 inch w.c. = 249 Pa.