Since the composition of natural gas can vary, it is not one of the fluid tables that is included with PIPE-FLO.  Users who are analyzing natural gas systems may want to consider using the methane table as described below if they do not have actual fluid data available.

Users who are analyzing a natural gas system often wonder if they can substitute methane for their system fluid. To answer this question, it will be helpful to look at the typical constituents of natural gas:

Constituent               %Volume
Methane (CH₄)             94.8%
Ethane (C₂H₆)              2.9%
Propane (C₃H₈)            0.8%
Butane (C₄H₁₀)             0.2%
Carbon Dioxide (CO₂)   0.1%
Nitrogen (N₂)                1.2%
TOTAL                         100%

Specific Gravity (rel. air =1): 0.586

Calculating the molecular weight of natural gas:

Methane              16.043 x 0.948 = 15.209
Ethane                   30.07 x 0.029 = 0.872
Propane               44.096 x 0.008 = 0.353
Butane                 58.124 x 0.002 = 0.116
Carbon Dioxide   44.009 x 0.001 = 0.044
Nitrogen              28.014 x 0.012 = 0.336
TOTAL                                             16.93

Since methane is the largest component of natural gas, it would be reasonably accurate to create a natural gas table that is an exact copy of the methane table with the exception that the molecular weight is changed from 16.043 to 16.93.

NOTE: This method should be used only if actual fluid data is not available for natural gas.  If actual data is available, users should either specify a custom fluid or build their own natural gas table.