installing gas piping

8/11/2019 Installing Gas Piping

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Installing gas piping

For any gas piping system, or special appliance, or for conditions other than thosecovered by the tables provided , such as longer runs, greater gas demands, orgreater pressure drops, the size of each gas piping system should be determined bystandard engineering practices

Proper sizing of the gas pipe assures thateach gas appliance receive enough gas to perform

safely and properly. The f goal of determining the pipe sizing of gas piping system is to be

assured that the gas pressure at the inlet to each appliance is sufficient.

To understand gas pipe size the following must be under stood

1. Natural gas delivery is measured in cubic feet. Gas deliver y is not a measure of pressure

however is a measure of volume at a given pressure.2. Gas pipe sizing is in cubic feet (cf)

3. Appliance gas use is measured in BTU (British Thermal Units) It is the amount of energy

needed to cool or heat one pound of water by one degree Fahrenheit.The heat value

(energy content) of fuels is expressed in BTUs.

I. A BTU can be approximated as the heat produced by burning a single wooden

match

II.

A BTU can be approximated as the amount of energy it takes to lift a one-pound

weight 778 feet (237 m).

4. Conversions must be made from BTU of the appliance demand to cubic feet of delivery of

gas

I. conventionally 1 MMBtu (1 million BTU) = 1.054615 GJ.[9]

II. The high or low heating value, energy content of a volume of natural gas varies

with the composition of the natural gas.

III.

There is no universal conversion factor for the number of BTU to volume. 1

standard cubic foot of typical natural gas yields 1030BTU

(a)between 1010 BTU and 1070 BTU,

(b)depending on quality, when burned

IV.

As an approximation, 1000 ft3of natural gas yields 1MMBTU 1GJ

V. 1 ft3of natural gas yields 1000 BTU

VI.

5. The specific gravity of the gas is needed ( the table ares based upon a specific gravity of

0.60)

Pro er Gas Pi e Size
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Residential gas system and the appliances all have the same, or nearly the same, requirement for

minimum gas pressure at the appliance inlet.

The average resinditial gas pressure is about 5 in. (1.2 kPa) w.c., which is enough for proper

operation of the appliance regulator to deliver about 3.5 in. (0.87 kPa) w.c.

There are other systems, however, where the required inlet pressure to the different

appliances could 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.

Additional requirements

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 factor would seldom be of concern in small systems

I the source pressure is psi (14 in. w.c.) (3.4 kPa) or less, should be verified for

systems with greater gas pressure at the point of supply.

recognizes that each appliance must be supplied with the minimum gas pressure

required by the appliance for proper operation at its inlet. The farthest appliance and the

highest appliance inlet demands must be met.


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General Pipe Sizing Considerations

To determine the size of piping used in a gas piping system, the following factors must be

considered:

1. Allowable loss in pressure from point of delivery to appliance

2. Maximum gas demand

3.

Length of piping and number of fittings

4. Specific gravity of the gas

5. Diversity factor

Pipe sizing based on the Longest Length Method.

This sizing method is conservative in its approach by applying the maximum operating

conditions in the system .

To determine the size of each section of gas piping in a system within the range of the

capacity tables, proceed as follows

1. Divide the piping system into appropriate segments consistent with the presence of

tees, branch lines, and main runs.

2.

For each segment, determine the gas load (assuming all appliances operate

simultaneously) and its overall length.

3. An allowance (in equivalent length of pipe) as determined fromTable B.3.2should

be considered for piping segments that include four or more fittings.
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4. Determine the gas demand of each appliance to be attached to the piping system.

5.

Use the Table to select the piping size, calculate the gas demand in terms of cubic

feet per hour for each piping system outlet. WhereTable 6.3(a)throughTable

6.3(m)are to be used to select the piping size, calculate the gas demand in terms of

thousands of Btu per hour for each piping system outlet.

6.

Where the piping system is for use with other than undiluted LP-Gases, determine

the design system pressure, the allowable loss in pressure (pressure drop), and

specific gravity of the gas to be used in the piping system.

7. Determine the length of piping from the point of delivery to the most remote outlet

in the building/piping system.

8.

In the appropriate capacity table, select the row showing the measured length or the

next longer length if the table does not give the exact length. This length is the only

length used in determining the size of any section of gas piping. If the gravity factor

is to be applied, the values in the selected row of the table are multiplied by the

appropriate multiplier from Table

9. Use this horizontal row to locate ALL gas demand figures for this particular system

of piping.

1. Starting at the most remote outlet, find the gas demand for that outlet in the horizontal row just

selected. If the exact figure of demand is not shown, choose the next larger figure left in the row.
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2. Opposite this demand figure, in the first row at the top, the correct size of gas piping will be

found.

3. Proceed in a similar manner for each outlet and each section of gas piping. For each section of

piping, determine the total gas demand supplied by that section.

When a large number of piping components (such as elbows, tees, and valves) are installed in a

pipe run, additional pressure loss can be accounted for by the use of equivalent lengths. Pressure

loss across any piping component can be equated to the pressure drop through a length of pipe.

The equivalent length of a combination of only four elbows/tees can result in a jump to the next

larger length row, resulting in a significant reduction in capacity. The equivalent lengths in feet

shown inTable B.3.2have been computed on a basis that the inside diameter corresponds to that

of Schedule 40 (standard weight) steel pipe, which is close enough for most purposes involving

other schedules of pipe. Where a more specific solution for equivalent length is desired, this can

be made by multiplying the actual inside diameter of the pipe in inches by n/12, or the actual

inside diameter in feet by n.Ncan be read from the table heading. The equivalent length values

can be used with reasonable accuracy for copper or brass fittings and bends, although the

resistance per foot of copper or brass pipe is less than that of steel. For copper or brass valves,

however, the equivalent length of pipe should be taken as 45 percent longer than the values in

the table, which are for steel pipe.
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The Branch Length Method.

This sizing method reduces the amount of conservatism built into the traditional Longest

Length Method. The longest length as measured from the meter to the farthest remote appliance

is used only to size the initial parts of the overall piping system. The Branch Length Method is

applied in the following manner:

1.

Determine the gas load for each of the connected appliances.

2. Starting from the meter, divide the piping system into a number of connected segments, and

determine the length and amount of gas that each segment would carry, assuming that all

appliances were operated simultaneously. An allowance (in equivalent length of pipe) as

determined from Table B.3.2 should be considered for piping segments that include four or

more fittings.

3.

Determine the distance from the outlet of the gas meter to the appliance farthest removed from

the meter.

4. Using the longest distance (found in Step 3), size each piping segment from the meter to the

most remote appliance outlet.

5.

For each of these piping segments, use the longest length and the calculated gas load for all of

the connected appliances for the segment and begin the sizing process in Steps 6 through 8.

6. Referring to the appropriate sizing table (based on operating conditions and piping material),

find the longest length distance in the first column or the next larger distance if the exact

distance is not listed. The use of alternative operating pressures and/or pressure drops requires

the use of a different sizing table but does not alter the sizing methodology. In many cases, the

use of alternative operating pressures and/or pressure drops requires the approval of both the

authority having jurisdiction and the local gas serving utility.

7. Trace across this row until the gas load is found or the closest larger capacity if the exact

capacity is not listed.

8.

Read up the table column and select the appropriate pipe size in the top row. Repeat Steps 6, 7,

and 8 for each pipe segment in the longest run.

9. Size each remaining section of branch piping not previously sized by measuring the distance

from the gas meter location to the most remote outlet in that branch, using the gas load of

attached appliances, and follow the procedures of Steps 2 through 8.


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Frequently used units for measuring natural gas:

1.

1 cubic foot (cf) 1,027 Btu

2. 100 cubic feet (1 ccf) 1 therm (approximate)

3. 1,000 cubic feet (1 Mcf) = 1,027,000 Btu (1 MMBtu)

4.

1,000 cubic feet (1 Mcf) = 1 dekatherm (10 therms)

5.

1 million (1,000,000) cubic feet (1 Mmcf) = 1,027,000,000 Btu

6. 1 billion (1,000,000,000 cubic feet (1 bcf) = 1.027 trillion Btu

7. 1 trillion (1,000,000,000,000) cubic feet (1Tcf) = 1.027 quadrillion Btu

8.

To convert 1 foot of water to psi. Feet of water x 0.4335= PSI. I divided .4335 by 12 (in

per ft) for a mult. of .036125. So, inches of water x 0.03625 = PSI. 1

(PSI)/0.036125=27.682...roughly 28"

Each appliance has a minimum input demand in BTUs per hour. The chart below gives someexamples of typical BTU demands.

Look at the chart to assist you in determining the proper pipe size for your job.

To convert from BTUs to cubic feet per hour divide BTU by 1100 (example: 50,000 BTU

by 1100 = 45.45 cubic feet of gas per hour).

To get BTU from cubic feet, multiply cubic x feet 1100 (45.45 cubic feet x 1100 = 50,000

BTU.)


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1. Approved gas piping fitting materials

Black iron and corrugated stainless steel (CSST) are commonly used approved materials. CSST

requires certification from the manufacturer for anyone who is going to purchase and install the

material.

1. Follow all applicable local and state codes, see the latest edition of NFPA 54 National

Fuel Gas Code.NFPA 54: National Fuel Gas Codeprovides industry-accepted guidance

for the safe installation and operation of fuel gas piping systems, appliances, equipment,

and accessories.

2.

Cutting pipe

If you are cutting iron pipe, you must ream the cut of your pipe so you maintain the full inside

diameter of the pipe.

3. Special instructions

Do not use ground joint unions except directly at the meter or after the shutoff valve at the

appliance. Each place where you will have a gas appliance must have a gas shutoff valve and drip

tee.

Any person who installs gas piping on property not under their ownership must possess a Gas

Piping Mechanic License. All gas piping installations require a permit and inspection.

5. Testing

I. Testing the system is your responsibility. The inspector does not perform the test or

provide any of the equipment necessary for the test, including test gauges.

Use Approved Gas Pipe

Installation


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II. An air pressure test is required. The test pressure shall be at least 1 times the working

pressure, but no less than 15 pounds per square inch (psi). The test duration shall not be

less than 10 minutes. The piping system shall withstand the test pressure specified

without showing any evidence of leakage or other defects.

III. Mechanical gauges used to measure test pressures shall have a range such that the

highest end of the scale is not greater than five times the test pressure. For instance, a 3

psi test will require a maximum 15 pound gauge

IV. The piping system shall be under test (pressurized) and the test gauge visible at the time

of inspection.

V. Where the gauge does not indicate the minimum pressure required for the test, or any

reduction of test pressures as indicated by pressure gauges during inspection shall be

deemed to indicate the presence of a leak.

VI. If there is a drop in pressure, check for leaks. Check for leaks by filling a spray bottle with

soapy water and spraying the solution on the pipe, where it meets the fittings. Bubbles

show a leak and you should repair it appropriately. Continue this process until you have

no leaks. Do not use an open flame to test for leaks.

VII. The pressure drop in the piping is subtracted from the source delivery pressure to verify

that the minimum is available at the appliance.VIII.

6. Inspection

I. At the time of inspection, be sure to leave all of the gas piping exposed so the inspector

can look at the whole system.

II. Have demand load ready to show

Minimum Demand of Typical Gas Appliances in BTUs Per Hour

Appliance

Demand in BTU/hour

Barbecue (residential) 40,000

Domestic clothes dryer 35,000


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Domestic Gas Range 65,000

Domestic Recessed Oven Section 25,000

Fireplace Gas Log 80,000

Gas Refrigerator 3,000

Storage Water Heater, 30-40 gallon tank 35,000

Storage Water Heater, 50 gallon tank 50,000

Example:

Problem: Determine the required pipe size of each section and outlet of the piping system

shown.

diagram of piping system

Solution:


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Maximum gas demand of outlet A - 35,000 BTU per hour/1100 BTU per cubic foot = 31.82 cubic

feet per hour.

Maximum gas demand of outlet B-3,000 BTU per hour/1100 BTU per cubic foot = 2.73 cubic

feet per hour.

Maximum gas demand of outlet C-65,000 BTU per hour/1100 BTU per cubic foot = 59.09 cubic

feet per hour.

Maximum gas demand of outlet D-150,000 BTU per hour/1100 BTU per cubic foot = 136.36

cubic feet per hour.

The length of pipe from the gas meter to the most remote outlet (outlet A) is 60 feet.

Using the column marked 60 feet on the size of gas pipe charge:

Outlet A, supplying 31.82 cubic feet per hour, requires one-half inch pipe.

Section 1, supplying outlets A and B, or 34.55 cubic feet per hour requires one-half inch pipe.

Section 2, supplying outlet A, B and C, or 93.64 cubic feet per hour requires three-quarter inch

pipe. Section 3, supplying outlets A, B, C, and D, or 230 cubic feet per hour, requires one-inch

pipe.

Using the column market 60 feet: Outlet B supplying 2.73 cubic feet per hour requires one-half

inch pipe. Outlet C, supplying 59.09 cubic feet per hour, requires one-half inch pipe.

Using the column marked 50 feet: Outlet D, supplying 136.36 cubic feet per hour, requires

three-quarter inch pipe.

.

Size of gas piping


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1.

Gas type is natural gas.2.

The inlet pressure is 0.5 psi or less.3.

The allowable pressure drop is 0.5 inches water column.4. The specific gravity of the gas being supplied is 0.60.

PIPE

SIZE

10 20 30 40 50 60 70 80 90 100 125

172 118 95 81 72 65 60 56 52 50 44 360 247 199 170 151 137 126 117 110 104 92

1 678 466 374 320 284 257 237 220 207 195 1731 1390 957 768 657 583 528 486 452 424 400 3551 2090 1430 1150 985 873 791 728 677 635 600 532

2 4020 2760 2220 1900 1680 1520 1400 1300 1234 1160 10202 1/2 6400 4400 3530 3020 2680 2430 2230 2080 1950 1840 1630

3 11300 7780 6250 5350 4740 4290 3950 3670 3450 3260 28904 23100 15900 12700 10900 9660 8760 8050 7490 7030 6640 5890

installing gas piping

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