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Engineering ToolBox > Natural Gas Pipe Size Calculator
The capacity of a low pressure natural gas (less than 1 psi) pipe line can be calculated with the Spitzglass formula like
q = 3550 k ( h / l SG)1/2 (1)
where
q = natural gas flow capacity (cfh)
h = pressure drop (in Water Column)
l = length of pipe (ft)
k = [d5/(1 + 3.6/d + 0.03 d)]1/2
d = inside diameter pipe (in)
SG = specific gravity
For natural gas the nominal BTU/cf varies from about 900 to 1100 BTU/cf. In general it is common to set
The specific gravity of natural gas varies from 0.55 to 1.0.
The downstream pressure in a houseline after the meter/regulator is in general in the range of 7 to 11 inches Water Column, or about 1/4 psi.
The capacity of a 100 ft natural gas pipe with a nominal diameter 0.5 inches (actual ID 0.622 in) and 0.5 in. WC pressure drop can be calculated as
k = [0.6225/(1 + 3.6/0.622 + 0.03 0.622)]1/2
= 0.117
q = 3550 0.117 ( 0.5 / 100 0.60 )1/2
= 37.9 cfh
The specific gravity of the natural gas is set to 0.60.