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# 1316.1.1 Longest Length Method

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The pipe size of each section of gas piping shall be determined using the
longest length of piping from the point of delivery to the
most remote outlet and the load of the section. [NFPA
54:6.1.1]

**Problem:**Determine the required pipe size of each section and outlet of the piping system shown in Figure 1316.1.1. Gas to be used has a specific gravity of 0.60 and 1100 British thermal units (Btu) per cubic foot (0.0114 kW•h/L), delivered at 8 inch water column (1.9 kPa) pressure. For SI units: 1 foot = 304.8 mm, 1 gallon = 3.785 L, 1000 British thermal units per hour = 0.293 kW, 1 cubic foot per hour = 0.0283 m

^{3}/h

**Solution:**

- Maximum gas demand of Outlet A -

32 cubic feet per hour (0.91 mMaximum gas demand of Outlet B -^{3}/h) (from Table 1308.4.1).

3 cubic feet per hour (0.08 mMaximum gas demand of Outlet C -^{3}/h) (from Table 1308.4.1).

59 cubic feet per hour (1.67 mMaximum gas demand of Outlet D -^{3}/h) (from Table 1308.4.1).

136 cubic feet per hour (3.85 m^{3}/h) [150000 Btu/hour (44 kW)] divided by 1100 Btu per cubic foot (0.0114 kW•h/L) - The length of pipe from the gas meter to the most remote outlet (Outlet A) is 60 feet (18288 mm).
- Using the length in feet column row marked 60 feet (18288 mm) in Table 1316.2(1):

Outlet A, supplying 32 cubic feet per hour (0.91 m^{3}/h), requires^{1}/_{2}of an inch (15 mm) pipe.

Section 1, supplying Outlets A and B, or 35 cubic feet per hour (0.99 m^{3}/h) requires^{1}/_{2}of an inch (15 mm) pipe.

Section 2, supplying Outlets A, B, and C, or 94 cubic feet per hour (2.66 m^{3}/h) requires^{3}/_{4}of an inch (20 mm) pipe.

Section 3, supplying Outlets A, B, C, and D, or 230 cubic feet per hour (6.51 m^{3}/h), requires 1 inch (25 mm) pipe. - Using the column marked 60 feet (18288 mm) in Table 1316.2(1) [no column for actual length of 55 feet (16764 mm)]:

Outlet B supplying 3 cubic feet per hour (0.08 m^{3}/h), requires^{1}/_{2}of an inch (15 mm) pipe.

Outlet C, supplying 59 cubic feet per hour (1.67 m^{3}/h), requires^{1}/_{2}of an inch (15 mm) pipe. - Using the column marked 60 feet (18288 mm) in Table 1316.2(1):

Outlet D, supplying 136 cubic feet per hour (3.85 m^{3}/h), requires^{3}/_{4}of an inch (20 mm) pipe.

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