Gas Pipe Sizing - Simple Sizing Method - Page 1 2 3 4 
SIMPLE METHOD OF NATURAL
GAS PIPE SIZING
A simple method of sizing Natural Gas pipes is to use the tables
below.
The three tables are for Steel, thin wall copper and thick
wall copper.
An allowance may be made for fittings.
This allowance is to add to the measured pipe lengths, 0.3
metres for 90o bends and 0.6 metres for an elbow or tee.
Procedure
1.
Measure the length of pipe in each section.
2.
Add equivalent lengths for fittings.
3.
Determine heat output of appliance or heat to
be carried in pipe in MW
4.
Divide this by Gross Calorific Value (GCV) of
gas i.e. 38.7 MJ/m3 to give gas flow rate in m3/s.
5.
Determine pipe size from relevant Table.
Example 1
Determine the steel pipe size for a gas boiler if the boiler rating
is 28 kW and the measured pipe run is 10.2 metres with 3 elbows.
Procedure
1.
Measure the length of pipe in each section – answer 10.2 m
2.
Add equivalent lengths for fittings – answer 3 x 0.6 = 1.8
m. Add to 10.2 m gives 12.0 metres.
3.
Determine heat output of appliance or heat to be carried in
pipe in MW. – answer 28 / 1000 = 0.028 MW
4.
Divide this by Gross Calorific Value (GCV) of gas i.e. 38.7
MJ/m3 to give gas flow rate in m3/s – answer 0.025 / 38.7
= 0.0007235 m3/s
5.
Determine pipe size from relevant Table – answer from Table
1 gives 20mm pipe because the flow rate lies between two values on the table
and the larger pipe size is chosen.
Table 1 below is used for Mild Steel pipe, BS 1387: medium grade.
Table 1 – Gas Pipe Sizing for Steel Pipe |
||||||||
|
Nominal Pipe
size (mm) |
Pipe length (m) |
|||||||
|
3.0 |
6.0 |
9.0 |
12.0 |
15.0 |
18.0 |
21.0 |
24.0 |
|
|
Gas Flow Rate
(m3/s) |
||||||||
|
15 |
0.00104 |
0.00072 |
0.00057 |
0.00050 |
0.00044 |
0.00039 |
0.00036 |
0.00034 |
|
20 |
0.00219 |
0.00149 |
0.00120 |
0.00102 |
0.00090 |
0.00083 |
0.00076 |
0.00071 |
|
25 |
0.00409 |
0.00275 |
0.00224 |
0.00193 |
0.00169 |
0.00153 |
0.00142 |
0.00134 |
|
32 |
0.00826 |
0.00574 |
0.00464 |
0.00393 |
0.00346 |
0.00315 |
0.00291 |
0.00275 |
|
40 |
0.01258 |
0.00865 |
0.00700 |
0.00598 |
0.00527 |
0.00480 |
0.00440 |
0.00417 |
Table 2 below is used for Copper
Tube Table ‘X’ or EN 1057 thin wall, half hard
temper.
Table 2 – Gas Pipe Sizing for Copper Tube Table ‘X’ |
||||||||
|
Nominal Pipe
size (mm) |
Pipe length (m) |
|||||||
|
3.0 |
6.0 |
9.0 |
12.0 |
15.0 |
20.0 |
25.0 |
30.0 |
|
|
Gas Flow Rate
(m3/s) |
||||||||
|
15 |
0.00079 |
0.00054 |
0.00043 |
0.00035 |
0.00032 |
0.00027 |
0.00025 |
0.00024 |
|
22 |
0.00244 |
0.00165 |
0.00126 |
0.00102 |
0.00110 |
0.00079 |
0.00070 |
0.00063 |
|
28 |
0.00495 |
0.00330 |
0.00260 |
0.00220 |
0.00197 |
0.00165 |
0.00142 |
0.00134 |
Table 3 below is used for Copper
Tube Table ‘Y’ or EN 1057 thick wall, half hard
temper.
Table 1 – Gas Pipe Sizing for Copper Tube Table ‘Y’ |
||||||||
|
Nominal Pipe
size (mm) |
Pipe length (m) |
|||||||
|
3.0 |
6.0 |
9.0 |
12.0 |
15.0 |
20.0 |
25.0 |
30.0 |
|
|
Gas Flow Rate
(m3/s) |
||||||||
|
15 |
0.00071 |
0.00047 |
0.00037 |
0.00032 |
0.00028 |
0.00027 |
0.00024 |
0.00020 |
|
22 |
0.00220 |
0.00149 |
0.00118 |
0.00094 |
0.00087 |
0.00072 |
0.00064 |
0.00057 |
|
28 |
0.00456 |
0.00307 |
0.00244 |
0.00205 |
0.00181 |
0.00149 |
0.00134 |
0.00118 |
It must be remembered that the above method of pipe sizing is not as
accurate as using the CIBSE guide method as detailed in page 3, but can be
useful for checking pipe sizes quickly.
Gas Pipe Sizing - Simple Sizing Method- Page 1 2 3 4