Chap5 Gas Reticulation System

GAS RETICULATION

SYSTEM

Assoc. Prof. Engr. Dr. Rahmat Bin Mohsin

Mohd. Dinie Muhaimin Samsudin

Storage and Reticulation System SKN 4223 2

TYPE OF GAS PIPELINE SYSTEMS

• Transmission

• Is a line installed for the purposed of transmitting gas

from a source or sources of supply to one or more

distribution centers or a pipe installed to

interconnected sources or supply.

• Transmission lines differ from gas distribution line in

that they operate at higher pressure, are longer and

have greater distance between connection


• Distribution

• Is a network of pipeline connecting the gas

from supply sources to the consumer

premises.

• Supply source are transmission line for

natural gas and bulk storage for liquefied

petroleum gas.


GAS PIPE DESIGN COMPONENTS

1. Pipeline optimization

2. Selection and analysis of pipeline route

3. Geotechnical and environmental aspects

4. Engineering survey

5. Route design

6. Buoyancy control

7. Selection of materials

8. Stress analysis

9. Facility design

10. Corrosion control


Basic Concepts of Gas

Distribution System (Gas Supply)

• Items to ensure stability of supply

High reliability

Low installation cost

Low maintenance

Materials and parts supply facilities

• Supply system is determined based on the serviced

area, volume of gas needed, the capacity of existing

equipment, the possibility of the expansion,

maintenance and control facilities and costs.


• In making the classification of consumers and

supply system, it is necessary to ensure the system is

safe and secure.

• Supply system is classified to:

1. Large industry -> 1000 cubic meters per hour

2. Medium and small industries

3. Commercial

4. Domestic - <1 cubic meter per hour


Government Acts

• Systems should be designed to comply with the requirements of the following acts:

• Petroleum Act (Safety Measures) 1984 Cover security measures to be considered in designing and installation of gas and petroleum-related facilities.

• Environmental Quality Act (1974) Act governing the activities that may affect the environment. Identify the mandatory environmental impact study

• Factories and Machinery Act (1967) To enforce the requirements of the tests carried out on a high-pressure gas pipe installation, including welding procedures, welder qualifications and other related.


Code of Practice and Standards

AGA : American Gas Association

ANSI : American National Standard Institute

ASME : American Society of Mechanical Testing

ASTM : American Society of Testing of Material

API : American Petroleum Institute

BS : British Standard

CSA : Canadian Standard Association

IP : Institute of Petroleum

ISA : Instrumentations Standards Association

MS : Malaysian Standard

MSS : Material Specification Standards

NACE : National Association of Corrosion Engineers

NEMA : National Electrical Manufacturing Association

PTS : Petronas Technical Standard

SIS : Standard Institution of Sweeden

SSPC : Steel Structure Painting Council


Design Factor and Class Location

• The thickness of the pipe is determined by design

factors as contained in ANSI / ASME B31.8.

• Class location is determined by calculating the density

of homes along the pipe to 200 m wide on the left and

right pipe during 1600 m.

Less than 10 houses Class I

10 to 40 houses Class II

More than 40 houses Class III

Storey building Class IV


DISTRIBUTION SYSTEM PIPELINE

• Using steel and plastic pipeline with pipe diameter

and pressure lower than the transmission pipeline

system.

• Consists of series of pipes that operate at

different pressures and there is no agreement or a

general statement or terminology on pressure

range for each classification.


• Before gas distributed to the user, it passes

through a series of gas stations in the system.

1. Local Stations

2. Area Station

3. Service Station

• Installation of the stations subject to the pressure

required by the user.

• Pressure reduced using pressure regulator.

• Odorizer included for security purposes.


BASIC CONSIDERATION IN SELECTING

THE DISTRIBUTION SYSTEM

• Three main factors should be considered:

1. Estimates the gas consumption rate or gas

demand

2. Selection and assumption of distribution

system (Network analysis)

3. Check the pressure required whether it is

maintained at a specific level


DESIGN DEMAND ESTIMATION

• Determination of the total amount of gas

consumption is among the first requirements for

the determination of the pipe diameter.

• What is required for the determination of the

total amount of gas consumption is the amount

of gas consumption of each combustion

appliances and the number of such appliances to

be installed.

• It can be determined directly from manufacturer.


Appliances Rating (Btu/hr)

Range, Free Standing Domestic Built-In Oven or Boiler Unit, Domestic

Built-In Top Unit, Domestic Water Heater, Automatic Storage (30 to 40 gal tank)

Water Heater, Automatic Storage (50 gal tank) Water Heater, Automatic Instantaneous:

Capacity : 2 gal. per minute Capacity : 4 gal. per minute Capacity : 6 gal. per minute

Refrigerator Gas Light

Incinerator, Domestic

65 000 25 000 40 000 45 000 55 000

142 800 285 000 428 000 3 000 2 500 35 000


• However, the amount of gas consumption

can be determine based on various factors

Number of customer

Type of residence

Fuel supply and demand situation

Kind of industries

Future prospect of the subject area


• In general the total amount of all rating of

appliances does not always amount of the gas that

each consumer uses. This is because, it is rarely the

case that consumers use all their appliances

simultaneously and the appliances are not always to

be used with the fully open.

• Therefore, the amount of gas to be considered as a

design consumption is a total gas consumption

the area multiply with consumption factor which is

called appliance gas coincident factor.


REQUIRED INFORMATION FOR

SERVICE PIPELINE DESIGN

The following information should be obtained:

• Plant layout

Overall plant layout

Part of plant layout where firing equipment is located

• Location of each burner system

• Required pressure of each equipment

• Future demand

• Location of natural gas service station and for LPG user

Existing LPG piping layout (This drawing must be checked to confirm its actual installation)

LPG supplied pressure

If possible, former LPG piping contractor name


PIPELINE ROUTE SELECTION

• Avoid side slopes and cross slopes

• Avoid unstable slope

• Avoid any crossing, if possible

river, highway, culvert etc

cross at straight section

• Avoid cemeteries

• Avoid national park or reserve land

• Avoid religious places

• Avoid community places

• Avoid pocket land


ROUTE OF SERVICES PIPING

SELECTION & CONSIDERATIONS

Following is the criteria to be considered to select services piping route.

• Exposed piping is much better than underground piping for easy maintenance and safety

• Gas piping shall not be installed in/at/through the following places or locations:

a lift shaft

exhaust duct, etc.

electrical facility room, etc.

where it will be subjected to extreme temperature, water or moisture continuously

where it will be subjected to excessive vibration

where it will be subjected to corrosive gas or solution

in concrete slab or cylinder


• Gas piping shall be securely supported to avoid strain exerting on the pipe. Therefore good pipe support must be considered too.

• The piping and its support must not obstruct the operation of any factory's mobile machine i.e. forklift and crane.

• Planning or possible expansion or modification of factory

where the future demand will be

whether the construction (of the expansion) will cause unsafe condition or modification required to the piping system.


• The construction or installation work of the

piping shall least affect the production or

operation of the factory.

• PE pipe shall not be installed as exposed pipe.

• The radius of the inner curve of PE pipe

bending (R) shall not less than 25 times of inner

diameter of the pipe.


• Location of customer's monitoring meter and

line of equipment/regulator shall be located in

ventilated spaces readily accessible for

examination, servicing or replacement.

• Piping system shall be as simple as possible to

avoid confusion, especially in case of existing

LPG piping remained.

• The loop of piping shall not be use for internal

piping


SIZING OF GAS PIPING FOR

SERVICE LINE

• Is a line connected from the street main to the

customer's meter.

• Gas piping shall be of such size and so installed

as to provide a supply of gas sufficient to meet

demand without undue pressure drop between

service station and gas appliances.


• Several points need to be considered when sizing the pipe;

2 ½ and 5 inches pipe shall not be used for new piping system except for a special case. These two pipes are not common in the market.

The pipe size of the piping system shall not be changed except for branches and connection for meters, regulators, isolation valves or special case such as tie-in point to existing piping etc.

The pipe size of the downstream pipe shall not be larger than upstream except the connection for meters, regulators, isolation valves etc. And the downstream pipe of meters or regulator must be adequate size for distributing condition.


• The minimum pipe size for welding is recommended to be 1 inch.

• Factors influence the service line sizing are:

Total connected load

Length of service line

Pressure at the main

• There are four methods widely used to solved the above task as called a quit and simple calculation (not as complex as general gas flow equation).

NFPA No. 54 (National Fire Protection Association) Method

Clifford Method

Cox's Formula

Pauls’s Formula


Elevation Effect to Low Pressure

System

• Consider gas with specific gravity of S at static

height of 1m:

At datum:

• Atmospheric pressure : Pa mbar

• Gauge Pressure : Pg mbar

• Absolute pressure : Pa + Pg mbar


• At 1m height, gauge pressure lower by

ρgas x g x H.


• At 1m height, atmospheric pressure is lowered

by rair x g x H.

rair = 1.2248 kg/m3


• Therefore,

• It shows that, the pressure drop for low pressure system

is:

0.12 (1 - S) mbar/m


COX'S FORMULA

• Supply Pressure is/above 29.4 kPa.G (3000

mmH2O).

• The pipe size of each section or portion shall be pre-

determined by using Table, which shows the

maximum flow capacity at various pressure to ensure

the flow velocity at various pressure to ensure the

flow velocity does not exceed 20 m/s.


• In case that supply pressure is not available in the Table, the maximum flow capacity of each pipe at 20 m/s can be calculated as below:

where,

Qmax : Maximum flowrate (Sm3/hr) at 20 m/s flow velocity

Ps : Supply pressure (kPa.G)

D : Pipe inner diameter (mm)

101.3 : Atmospheric pressure in kPa

Qmax 1.8

102 x x D

2 x

101.3 Ps

101.3


• The pressure drop of the size pre-determined above to each appliance system shall be calculated by Cox's Formula as shown below: However, maximum allowable pressure drop is 15% of supply pressure. If not, shall select bigger pipe size for that sections to provide the sufficient pressure or pressure drop within 15% of supply pressure.

• In that case, piping cost effect should be also taken into consideration, so that 2 or more piping sections or portions might be selected to bigger pipe size. This mean that, the down stream pipe size must be bigger size than upstream pipe.


• Where,

P1& P2 : Absolute pressure (kPa.abs) = Gauge Pressure (kPa.G) + Atmospheric Pressure (101.325 kPa)

S : Specific Gravity

Q : Flowrate (Sm3/hr)

L : Distance (m)

D : Pipe Inner Diameter (mm)

K : Cox's Coefficient = 1.69 x 10-3

Q K P

21 P

22 D

5

S L

P2 P21

S Q2 L

K2 D

5


Example 1

• Determine pipeline sizing of a domestic installation

diagram shown below. Assume SG = 0.6


Solution

a) Piping Diagram


b) Design flowrate and pre-determined

Node No. Flowrate Sm3/h Pipe Size (inch)

0-1 395 3 (2 ½)

1-2 95 1

2-3 35 ¾

2-4 60 1

1-5 300 2


c) Pressure Drop Calculation

As supply pressure is 138 kPa.G, the minimum pressure to the equipment is 117.3 kPa.G (218.6 kPa.abs). Therefore, pressure drop of each pipe as shown in the following table.


Node No. Flowrate (Sm3/h)

Length (m)

Pipe size (inch)

Pipe size (mm)

P1 (kPa.abs)

P2 (kPa.abs)

Remarks

0-1 395 100 3 77.92 239.3 236.7

1-2 95 70 1 26.64 236.7 222.1

2-3 35 65 ¾ 20.96 222.1 211.8 <218.6

2-4 60 40 1 26.64 222.1 216.6 <218.6

1-2 95 70 1 ¼ 35.08 236.7 233.1

2-3 35 65 ¾ 20.96 233.1 227.8 >218.6

2-4 60 40 1 26.64 233.1 227.8 >218.6

1-5 300 50 2 52.48 236.7 231.2 >218.6


d) Result


Example 2

• A horizontal liquefied petroleum gas pipeline planned to be installed a the Gas Engineering Laboratory as shown in figure. Liquefied petroleum gas is supplied through a bulk tank, which has a wetted area of 90 square feet and a minimum rate of evaporation of 13.3875 Ib/hr. The Gas Engineering Department has signed the agreement with a supplier for the supply of liquefied petroleum gas composition as shown in table in order to achieve the latent heat of evaporation and the heat of combustion are 160 Btu/Ib and 21422 Btu/Ib, respectively. If the surrounding temperature and overall heat transfer coefficient is 80oF and 3 Btu/ft2.oF respectively, calculate the pipe size of each section involved.


Composition Percent Volume

Propane 55

i-butane 30

n-butane 15


FT

T

TAQ

hBtu

LQ

hlbQ

o

v

R

06.72

80×90×32142

'

/2142

160×3875.13

×3875.13'

/3875.13

2

2

vap

AAAA PxPyP


Comp %V V (gal) ρ

(Ib/gal)

W MW mol x Pvap at

72.06oF

x. Pvap y y.MW

C3 55 0.55 4.16 2.288 44 0.052 0.5843 150 87.645 84.33 37.1052

n-C4 30 0.30 4.81 1.443 58 0.025 0.2809 34 9.5506 9.19 5.3302

i-C4 15 0.15 4.64 0.696 58 0.012 0.1348 50 6.740 6.48 3.7584

0.089 103.9356 100 46.1938

6019628

193846

9628.

.

.

.

AMWSG


• Supply Pressure = 100 kPa.gauge

• Minimum Pressure = 85 kPa.gauge =186.3 kPa.abs

• Pre-determine

Node Q (Sm3/h) Pipe size (inch)

0-1 395 2 ½ (3)

1-2 95 1

2-3 35 ¾

2-4 60 1

1-5 300 2

523

22

12

1069.1 Dx

LSQPP


Node No. Flowrate (Sm3/h)

Length (m)

Pipe size (inch)

Pipe size (mm)

P1 (kPa.abs)

P2 (kPa.abs)

Remarks

0-1 395 100 3 77.92 201.3 198.2

1-2 95 70 1 ¼ 35.08 198.2 193.9

2-3 35 65 ¾ 20.96 193.9 182.0 < 186.3

2-4 60 40 1 26.64 193.9 187.5 > 186.3

2-3 35 65 1 26.64 193.9 190.3 > 186.3

1-5 300 50 2 52.48 198.2 191.6 > 186.3


PAUL'S FORMULA

• Supply Pressure is less than 29.4 kPa.G (3000 mmH2O)

• Pressure drop of each section can be calculated by Paul's Formula as shown below:

ΔP : Pressure drop (Pa)

K2 : Paul's coefficient

= 7.09 x 10-4

D : Pipe inner diameter (mm)

S : Specific gravity of gas

L : Pipe length (m)


Q K2 P D

5

S. L

or

P S

K2 D5 x Q

2 L


• The Paul's Formula can be simplified as the

following formula which is based on Tokyo

Gas experiences.

ΔP : Pressure drop (Pa)

L : Pipe length (m)


P K'2 Q

2 L


• where, K'2 as shown in table below. (K'2 is also taken

into consideration of the pressure drop at fittings).

Nominal Pipe Size (inch)

K’2 Nominal Pipe Size (inch)

K’2

½ 5.20 3 6.67 x 10-4

3/4 8.80 x 10-1 4 3.94 x 10-5

1 2.37 x 10-1 6 3.94 x 10-5

1 1/4 5.31 x 10-2 8 3.02 x 10-6

1 1/2 2.29 x 10-2 12 4.14 x 10-7

2 7.85 x 10-3


• If the supply pressure is very low, the pressure

differences caused by difference of pipe level cannot

be neglected. Therefore, pressure differences shall be

considered and calculated by the formula as shown

below.

PH r . g. 1 S. H 12.68 x 1 S. H

PH : Pressure difference Pa

r : Density of air 1.293 kg/Nm3

S : Specific gravity of gas

Difference of pipe level m

g : Gravity acceleration 9.807 kg/s2


• If level of the node is higher than level of the last

node, the pressure drop is ΔP pressure calculated by

Paul's Formula minus ΔPH.

• The pre-determined of pipe size shall be named as

node number normally as node 0 (started - service

station), the next branch is named as node 1 and to

the end by following manner:

1. The longest length of piping from node n to the

end value shall be measured (Ln)


2. Calculate the K value with below formula:

K

Pn.max

Q2n Ln

Pn.max Pn 1.max Pn1

Pn.max : Maximum allowable pressure drop from node n to the end value

Pn1 : Pressure drop of section n1 calculated by determined pipe size

Qn : Design flowrate of section n


3. Compare K value to K'2 value shown in the

table. Then find out the appropriate pipe size of

corresponding K'2 (the value selected for K'2

should be less than K value). The selected pipe

size is known as pre-determined pipe size for

section n.

4. Pn shall be calculated by Paul's Formula

5. Repeat (1) – (4) to determine the pipe size of

section n + 1 until the end section.


Example

• Determine the pipe size below. The maximum allowable

pressure drop is 3 kPa.


Solution


• Pre-determine pipe size

• The most long pipe length from service station to

equipment is 0 - 4. Then,

• Node 0 to Node 1

K Pn.max

Q2n. Ln

3000

902 x 100

3.7 x 103

Therefore : Pipe Size 3"

Pressure drop K'2 Q

2 L

6.67 x 104

x 902 x 10 54.0 Pa


• Node 1 - Node 2

K Pn.max

Q2n. Ln

3000 54

602 x 90

9.1 x 103


Pressure drop K'2 Q

2 L

7.85 x 103

x 602 x 30 847.8 Pa


• Node 2 - Node 3

K Pn.max

Q2n. Ln

3000 54 847.8

202 x 20

2.6 x 101


Pressure drop K'2 Q

2 L

2.37 x 101

x 202 x 20 1896 Pa


• Node 2 - Node 4

K Pn.max

Q2n. Ln

3000 54 847.8

402 x 60

2.19 x 102


Pressure drop K'2 Q

2 L

7.85 x 103

x 402 x 60 753.6 Pa


• Node 1 - Node 5

K Pn.max

Q2n. Ln

3000 54.0

302 x 5

6.5 x 101


Pressure drop K'2 Q

2 L

2.37 x 101

x 302 x 5 1066.5 Pa


• Determination of pipe size

Node Flowrate (Sm3/h)

Length (m)

Pre-Size (inch)

ΔP (Pa)

Pipe Size (inch)

ΔP (Pa)

0 – 1 90 10 3 54.0 2 635.8

1 – 2 60 30 2 847.8 2 847.8

2 – 4 40 60 2 753.6 2 753.6

0 – 4 1655.4 2237.2

2 – 3 20 70 1 1896.0 1 ¼ 424.8

0 – 3 2797.8 1908.4

1 – 5 30 5 1 1066.5 1 1066.5

0 – 5 1120.5 1702.3


NFPA 54

• Noted for simplicity

• Given a length and the maximum load, the required pipe size is read directly from the table

• Following factors are required.

1) Allowable loss in pressure from point of delivery to equipment

2) Maximum gas demand

3) Length of pipe from the point of delivery to the most remote

4) Specific gravity of gas

5) Diversity factor


• Capacities for low pressure (0.5 psig or less) in cubic feet per hour of 0.60 specific gravity for different length are shown in Table 13 to Table 16 ( MS 930) for iron pipe or equivalent rigid pipe.

- Table 13 and 15 are based upon a pressure drop 0.3 inches water column

- Table 14 and 16 are based upon a pressure drop 0.5 inches water column

- Table 26 is used when capacities in thousands of BTU per hour of undiluted liquefied petroleum gases based on pressure drop 0.5 inches water column.


• If the data does not give the exact value, select the

column showing the next larger

• If the gravity of gas is different with table 13 to 16,

use the gravity factor in Table 25

• In using these tables no additional allowance is

necessary for an ordinary number of fittings.


Example

• Determine the required pipe size of each section and

outlet of the piping system shown below. Given gas

gravity 0.65, designed pressure drop is 0.5 inches water

column and gas heating value is 1000 BTU/CF.

Point of delivery Outlet C Range: 75,000 Btu/hr

Outlet B Gas refrigerator: 3,000 Btu/hr

Outlet A Water heater: 30,000 Btu/hr

Outlet D Furnace: 136,000 Btu/hr

10 '

20 ' 10 '

15 '

20 '

10 '

10 '

5'

Section 3 Section 2 Section 1


Solution

• Step 1

Maximum gas demand at each outlet

= Consumption Rating (Btu/hr)

Heating Value of Gas (Btu/cf)

Outlet A = 30,000/1000 = 30 cfh

Outlet B = 3,000/1000 = 3 cfh

Outlet C = 75,000/1000 = 75 cfh

Outlet D = 136,000/1000 = 136 cfh


• Step 2

Length of pipe from the point of delivery to the most remote outlet (A) = 60 ft

• Step 3

Refer to table which follow the above specification. Read under column length of 60 ft.


Section Outlet Demand (cfh)

Pipe Required (inches)

1 A B

30 3

3/8 1/4

A + B 33 3/8

2 C 75 3/4

A+B+C 108 3/4

3 D 136 3/4

A+B+C+D 244 1

If the gravity factor is applied to this example, the value in the column marked 60 feet of Table 14 would be multiplied by the multiplier 0.96 from Table 25 and resulting cubic feet per hour values would be used to size the piping.


Based on SG 0.6 at 60 feet (cfh)

Multiplier 0.96 (cfh)

Nominal Iron Pipe Size (inches)

16 15.36 1/4

36 34.56 3/8

68 65.28 1/2

178 170.88 3/4

260 249.60 1

520 499.20 1 1/4

810 777.60 1 1/2

1520 1459.20 2

2400 2304.00 2 1/2

4300 4128.00 3

8800 8448.00 4


Clifford Method

• May not be simple but offers the advantage of

flexibility

• Can be noted with actual pressure drop and pipe

size

• Which ultimately may prove useful when making

adjustments for possible future loads.

• Classified by two categories

1) Low pressure line

2) High pressure line


Low Pressure Line

• Five factors should be considered

i) Pipe length together with additional length of

fitting

ii) Allowable pressure drop

iii) Load or demand

iv) Pipe material

v) Actual pressure drop

• Refer to Table 28 and Table 29


Pipe Length

• Length 10 - 100 feet

Listed in left hand side of the table

• Length > 100 feet

The actual length (plus the allowable for fitting) and

allowable pressure drop are both divided by a

convenient number that will bring the pipe length

within the range of the table


Example

• 280 ft line with allowable pressure drop 0.6 inches

water column.

• The pipeline would be properly sized if the length is

considered to be 70 (divided by 4) and the allowable

pressure drop is 0.15 inches water column.

• Equivalent length for fitting refer to Table 29.

Commonly, 2 inches pipe size used as a reference. If

the final result (pressure drop) more than allowable

value select the next larger size.


Allowable Pressure Drop

• Is given over to pressure drop ranging from 0.1 to

1.0 inches water column.

• This pressure drops makes the table quit flexible

and allow for appropriate selection.

• Allowable pressure drop used is 0.6 inches water

column.

• Single line pipeline is direct solving but branch

lines must be sized separately.


Load or Demand

• Calculate the load it must handle.

• A branch line is sized on the basis of the BTU

rating of the appliance it services.

• The main line must handle the total load.

• An intermediate line will be sized for the

appliances it services.


Pipe Material

• Four type of piping material system and practitioner

will make his selection on the basis of company

practice.

Actual Pressure Drop

• For the more complicated piping system it is helpful to

determine the actual pressure drop for the pipe sized

selected.


Example

• Determine pipeline sizing of a domestic installation

shown below. Used allowable pressure drop is 0.6 inches

water column.

R

AB

C

D

15 feet, 0.34 " W C

5 feet,

0.26 " W C

10 feet, 0.26 " W C

10 feet,

0.26 " W C

Water h eater

30 ,0 00 Btu

Gas Rang e

63 ,0 00 Btu

Floo r furnace

80 ,0 00 Btu


Solution

• Step 1

Leading to the appliance with the greatest load or input.

Equivalent length:

Main line

Measured length = 15 feet

One 90 degree elbow = 5 feet

Sub-Total = 20 feet

Branch line to floor furnace (The Greatest Load)

Measured length = 5 feet

Tee-Side Outlet = 10.4 feet

Sub-Total = 15.4 feet


• Total pipe length from furnace to the pressure regulator is 35.4 feet

Since the main line is 0.57 of total length involved and 0.57 pressure drop of 0.6 inches water column is 0.34 inches water column. So allowable pressure drop on each branch line is 0.26 inches water column


• Step 2

Load demand based on figure:

Gas range = 63,000

Water heater = 30,000

Floor furnace = 80,000

Total Load = 173,000 Btu


• Step 3

Can select out of 4 type of piping material (use Table 28)

Main line

Pipe Sizing

Pipe length 20 ft and 0.34 " W.C. (allowable pressure drop)

(Select the suitable piping material) to the total load 173,000

Btu (if not available, look the next larger i.e. 321,000 Btu -

interpolation).

Answer = ¾ " IPS


• Actual Pressure Drop

From 3/4 inch IPS, proceed to RHS to 175,000 BTU (nearest to 173,000 Btu).

Then proceed upward until in line with the pipe distance 20 ft.

Answer = 0.1 inches water column


• Branch Line B

Pipe sizing and actual pressure drop

Use the similar way as above (main line)

Pipe length

= 20 ft (10 ft. measured length + 10 ft. Tee-Side)

Allowable pressure drop = 0.26 " W.C.

Load (63,000 Btu) = 109,000 Btu (interpolation)

Pipe size = 1/2 " K Tubing

Actual pressure drop = 0.1" W.C.

(Nearest load = 68,000 Btu)


• Branch Line C Pipe sizing and actual pressure drop. Use the similar way as

above (main line). Pipe length = 20 ft (10 ft. measured length + 10 ft. Tee-Side) Allowable pressure drop = 0.26 " W.C. Load (30,000 Btu) = 54,000 Btu (interpolation) Pipe size = 3/8 " K Tubing Actual pressure drop = 0.08" W.C. (Nearest load = 31,000 Btu)


• Branch Line D Pipe sizing and actual pressure drop. Use the similar way as

above (main line). Pipe length = 15 ft (5 ft. measured length + 10 ft. Tee-Side) Allowable pressure drop = 0.26 " W.C. Load (80,000 Btu) = 126,000 Btu (interpolation) Pipe size = 1/2 " K Tubing Actual pressure drop = 0.11" W.C. (Nearest load = 84,000 Btu)


High Pressure Line

• If an appliance requires gas at a pressure of 10 psig or

15 psig for proper operation, it will have to supplied by

a high pressure gas line.

• The carrying capacity of a pipeline is 10 times or 15

times greater with high pressure gas than with low

pressure.

- Table 31 to Table 34 (MS 930) have to be used

for Option 1

- Chart in Figure 19 (MS 930) has to be used for

Option 2.


• The increased capacity depends, of course on the

pressure at which the gas is piped and allowed pressure

drop.

• If an existing low pressure line has become overload, its

capacity may be increased considerably by increasing the

pressure by only a few pounds.

• In many such cases it would be less expensive and

provide better performance to change to two-stage

regulator rather than replace the existing low pressure

line.


Table 31 (MS930)


Example (Table 31)

• A commercial installation is to be made in a northern

area where the lowest temperature to be accounted is -

15oF. The pipe length is 40 ft and the maximum load is

650,000 Btu. Determine the required pipe size for

intermediate pressure line when two-stages regulator

will used.


Solution

• Step 1

Referring to the key at the bottom of Table 31, it will be noted that for

a minimum temperature -15oF, the B capacities should be used.

• Step 2

Select 40 ft in the left hand column of the table and use the pipe

capacities shown opposite the letter B.

• Step 3

Since the Figure 650, representing the load in thousands of Btu does

not appear in the horizontal line opposite 40 ft B the next higher figure

870 is selected.


• Step 4

Moving upward from the 870 just selected the required pipe size is found to be ½ inch type K tubing. By following the same procedure in the right of the table, ½ inch pipe will be indicated for this installation.

Note: For sizing high pressure lines involving factors beyond the scope of the simplified in Table 31, Table 32 to Table 35 are recommended.


Example (Option 1)

• Determine the proper pipe sizes for the high piping

system shown below. The maximum allowable

pressure drop between the high pressure regulator

outlet and several appliances is 5 psig

RL1 20 0 feet

L4

20 feet

L2 2 5 feet

L3

20 feet

2,00 0,000 Btu

1,50 0,000 Btu

3,00 0,000 Btu

Delivered

pressure

10 p sig

Initial

pressure 15 psig


• Step 1

An arbitrary decision must be made as to how this will be apportioned.

Suggested:

Main line = 3 psi

Each branch = 2 psi

Therefore, delivered pressure for the main line will be 12 psi and this will then be the initial pressure for the branch lines.


• Step 2

Referring to Table 33.

15 psi initial pressure it will be seen that the value of 'h' for 3 psi pressure drop is 169.

For each branch lines the initial is 12 psi and the pressure drop is 2 psi. For this pressure drop and initial pressure the value of 'h' is 103


• Step 3 Size the main line Pipe length = 200 ft Value of 'h' = 169 Load = 6500 thousand Btu (total load) Since 200 ft is not shown in the pipe sizing table. It is necessary to make

adjustment such as the following: 200 ft value of 'h' 169 100 ft value of 'h' 85 In table 32, the values 80 and 90 are found for 'h'. Since 85 is haft way

between, one can follow down between the two line to the standard pipe section.

The indicated pipe sized = 1 1/4 IPS


• However, the actual value of 'h' can be estimated.

Find 6500 in the horizontal line opposite to 1 ¼

IPS: 6684 is selected

• Proceed upward to the 100 ft line it is seen that the

actual value of 'h' appears to be 40. Since pipe

length and 'h' were divided by 2, it is necessary now

multiply by 2 to get the true value of 'h' for the size

selected.


• Size the line 2 Pipe length = 25 ft Value of 'h' = 103 Load = 3000 thousand Btu Since 'h' with 103 is not shown in the pipe sizing table. It is

necessary to make adjustment such as the following: The value of 'h' and the load by 4, as follow; Value of 'h' 103 Value of 'h' 26 Load 3000 thousand Btu Load 750 thousand Btu


• The problem can now be solved on the basis of the following factors:

Pipe length = 25 ft

Value of 'h' = 26

Load = 750 thousand Btu

Using table as already explained;

Pipe size = ½ IPS

Value of 'h' = 10 x 4 > (chart shown factor)

= 40


• Size the line 3 Solved in the same manner and the following factors being used with

the pipe sizing table. Pipe length (2 ells) = 30 ft Value of 'h' = 26 Load = 500 thousand Btu Value of 'h' 103 Value of 'h' 26 Load 2000 thousand Btu Load 500 thousand Btu Pipe sized = ½ IPS Actual value of 'h' = 6 x 4 = 24


• Size the line 4 Sizing line 4 follow the same procedure: Pipe length (2 ells) = 30 ft Value of 'h' = 26 Load = 375 thousand Btu

Value of 'h' 103

Value of 'h' 26

Load 1500 thousand Btu

Load 375 thousand Btu

Pipe sized = ½ IPS

Actual value of 'h' = 3 x 4 = 12


Example (Option 2)

• Find the proper size of standard weight pipe for a

1000 ft line which is to carry a load of 10,000,000

Btu/h. The initial pressure is 20 psi and the pressure

drop is limited to 3 psi.


Solution

• Step 1

Refer to table 33 : h = 199

Use Figure 19.

Align this point on Figure 19 with 1000 ft and extending to Line 3.

• Step 2

Align point on Line 3 with 10,000 of Scale 4 and extend to Scale 5. However, no pipe size can be read because out of range (no intersection).


• Step 3

Divide the 10,000 thousand Btu by 10 and repeat Step 2.

Pipe size in between 1 ½ " and 2 "

Answer: Select pipe size with 2 "


• Step 4

To find actual pressure drop with pipe size selected, reversed the above procedure.

Start with 2" pipe size.

Answer :

h value = 110

pressure drop in between 1 ½ psi and 2 psi.


BUOYANCY CONTROL

• Pipeline are subject to buoyant forces when they

encounter free-standing or flowing water at river

crossing, streams and lakes and when buried in the

saturated soils generally present in flood plains,

marshes, swamps, muskeg (bogs) and local depressions.


• There are two principles reasons for counteracting the buoyant force exerted on a pipeline system:

i) to submerge the pipe in a water-filled ditch during construction prior to backfilling

ii) to prevent the pipe from floating or rising off at the ditch bottom during the post installation period and during operation of the pipeline.


• Potential areas requiring buoyancy control can be classified into four brad categories:

i) river crossings

ii) stream or creek crossings

iii) muskeg or bogs crossing

iv) soil which have the potential to act as a fluid


Buoyancy control may be achieved in three ways: i) mechanical anchoring system

They are not commonly used for large diameter pipelines


ii) Backfill

• Using either native or borrowed material for buoyancy control, relies on the mass of the backfill over the pipe to counteract the buoyancy forces.

• Native backfill may be considered if it consists of stable, ice-free soil which is capable of achieving a reasonable level of strength.

• If the native backfill is not adequate, select backfill can be used. Select backfill should be coarse-grained, free draining material exhibiting sufficient shear strength when thawed or mixed with water.

• Although gravel is undoubtedly the best material, other materials such as a mixture of gravel, sand, clay and silt can be used


iii) density anchoring system

Density anchors are a system of weight added to the pipeline.

The types of anchors usually in the form of concrete are

1. swamp weights (saddle or set-on weights)

2. river weights (bolt-on)

3. continues concrete coating.


HookReinforced Bar

Wire Mesh

Rockshield


Hook

Rockshield

Wire Mesh

Bolt

Steel Tubing


Concrete Minimum Thickness, T

FBE Coating or equivalent

Compressible Material of Coating Protection

Wire MeshCompressible

Material


ANCHOR SELECTION

• Final selection of the type and extent of buoyancy control measures should be made on a site-specific basis, taking the following into consideration:

i) type of terrain

ii) type of soil

iii) ditch conditions (dry or wet)

iv) construction season

v) cost (economics)

vi) availability of materials

vii) access to site

viii) ease of handling during transport and construction

ix) limitations of equipment


ANCHOR DESIGN

CONSIDERATION

• In general, design of buoyancy control system are based on location conditions. For example, the following values or factors are incorporated into design calculation in Canada:

i) For river flood plains, small streams, drainage course, swamp, muskeg, small lakes and local depression where water will be encountered in the ditch during construction:

Negative Buoyancy : 5%

Fluid Density : 1040 kg/m3


• For main river channels and areas where flowing or moving water will be encountered during construction:

Negative Buoyancy : 10 %

Fluid Density : 1000 kg/m3


• However, in Malaysia design of buoyancy

control system is constant which is based on

negative buoyancy as 20 percent in all conditions

and density of fluid is 1000 kg/m3.


PIPELINE TESTING

• Pipeline testing required if the pipeline operates at

Hoop Stress of more than 30% of SMYS.

• Required to ensure that all connections are sealed and

without expansion

• performed after completion of installation activities

except tie-in part or the location of the testing is not

appropriate.

• Required by all code-gas code of practice

• It should be witnessed by the local gas inspector to

make verification


• There are two types of pipeline tests carried out

1. Hydrostatic test - test medium: water or methanol

2. Pneumatic test - test medium: compressed air or

inert gas

• Test pressure must be higher than the maximum

operating pressure and is usually 1.5 times the

design pressure.


• An important aspect of any operational testing is complete and accurate documentation - records remain as long as the equipment or piping is used.

• According to the Federal Pipeline Safety Regulations, USA, records must have the following information:

1. Pressure record chart 2. Equipment calibration test data 3. Name of the responsible operator 4. Date and time of test 5. Testing pressure 6. Testing medium 7. Description of testing equipment 8. Comments


HYDROSTATIC TEST

• General Guideline- Testing Part

1. Pipe Length < 16 km

2. For testing medium other than water, testing

capacity lower than 500 m3.

3. Determination of low and high pints, and testing

pressure.

4. Pipe ends nearby water resources are preferred.

5. All parts tested with equal diameter and pressure.


Hydrostatic Test Calculation

• Using standard forms and determination of the

required pressure test involving:

1. Location of the test

2. Pipe dimension

3. Low and high pints, and testing pressure.

4. Grade or pipe SMYS

5. Maximum operating pressure


Preparation before the

Performing Test

• Step 1: Approval to pump the water, if necessary

• Step 2: Testing Equipments:

a) Pressure and temperature recorder

b) Test head

c) Dead Weight Tester

d) Pressure and temperature gauge, if necessary

e) Flowmeter

f) Fittings - used to connect all equipment


• Step 3: Water filling

a) Water must not containing mud, floating materials or corrosive components unless it can be removed or treated.

b) The filling made with poly pig (front) or coated form pig.

c) Avoid air trapped in the pipeline - Will affect the testing process - Hazardous conditions

d) Check the head to prevent leakage test after completing the filling of water


• Total volume of water is determined by the

following methods:

a) The volume of water to be filled for the test:

Where

V = volume of water at 0 psig, gallon

L = length of test pipe, feet

D = internal diameter, inches

LxDxV 20408.0


b) The volume required at testing pressure

Vtp = content of water (gal) at pressure P and

temperature T, gal

Fwp = compressibility correction factor due to

water pressure changes from 0 psig to the

pressure P test

pwtppwptp FxFxFxVV

atm

test

wp

P

Pxx

F5105.41

1


FPP = correction factor of the internal volume of the

pipe as a result of pressure changes from 0

psig to the pressure P test

Where

D = external diameter of the pipe, inches

t = pipe wall thickness, inches

T = temperature of pipe, oF

60106.31030

9.01 66

Txxx

Px

t

DF test

pp


Fpwt = volume of water and volume of pipe correction factor due to temperature changes from base temperature (60oF) to the pipe temperature (oF)

Fpt = pipe volume correction factor due thermal expansion

FWT = specific volume of water correction factor due to thermal changes.

wt

pt

pwtF

FF

6102.18601 xxTFpt


Example 1

• Calculate the volume of water required

during the filling and pressure testing

Pipe Size: 10.75 inch OD x 0.279 w.t. X52

Length: 5 miles (5280 feet = 1 mile)

Test Pressure: 2430 psig

Temperature: 50oF


Solution

gallonLxDxV 888,1110408.0 2

007479.1

73.14105.41

1

5

test

wpP

xx

F

002804.160106.31030

9.01 66

Txxx

Px

t

DF test

pp

999818.0102.18601 6 xxTFpt

)(9993061.0 tablefromFwt

gallon

xxx

FxFxFxVV pwtppwptp

099,113

000512.1002804.1007479.1111888


Example 2

• After some time, testing pressure P was reduced to

2422 psig and temperature of the water and pipe

has been reduced to 48oF. Determine the volume

of testing at the time.


Solution

000565.1

999217.0

999781.0

002796.1

007454.1

48

2422

888,111

1

1

1

1

1

1

1

pwt

wt

pt

pp

wp

o

F

F

F

F

F

FT

psigP

gallonV

gallon

xxx

FxFxFxVV pwtppwptp

101,113

000565.1002796.1007454.1111888

1


• Initial volume = 113.099 gallons

• Volume of water required fro the second condition=

113.101 gallons

• Therefore, 2 gallons of water needed to be added to the

system.

• If, more water filled to achieve 2430 psig, the system is

leaking.


The Relationship Between

Pressure And Temperature

• Estimation of pressure changes due to changes in

water temperature can be determined by the chart.

• Performed with the use of charts based on the ratio

between the diameter and thickness of pipe involved.


Example

Size of pipe = 18 inches OD x 0375 inches w.t.

Initial temperature = 70oF

The previous temperature T ‘ = 66oF

Pressure = 1800 psig test


solution

According to the chart available pressure

drop is

FeTemperaturAverage

t

D

o682

6670

48375.0

18

FperpsigP o23


• Step 4: Pressuring

• Pressuring - typically use reciprocating pumps up

the pressure leak test

• The calculation of pressure tests should consider

the actual height in the area

• Pump stopped when the pressure reaches the leak

test pressure for a minimum of 30 minutes (time

stability of the pressure wave)

• Visually - check all the connectors


• Step 5: Test 24 hours (unless specified by the authorities involved)

• Pump to started to increase pressure to test pressure

• If the pressure falls more than 70 kPa within two hours, it must be re-pressurised

• Pressure is released through the test head when the pressure exceeds the test pressure.

• 24 hours started after the pump is removed from the pipe system

• Pressure and temperature recorded for 36 hours 1. Pressure increment 2. Leak testing 3. Period of stability 4. Test within 24 hours (methanol only six hours required) 5. Pressure reduction


• Step 6: Pressure reduction

• Performed after the completion of the test.

• Pressure reduced to a maximum of 2000 kPa for

pipes with a diameter of 60.3 mm or more in

order to avoid the effects of vibration - broken

pipe

• Water drained away from the pipeline trench.


• Step 7: Water Draining

• Water can be transferred to next part for testing

(if necessary) or be drained to suitable location.

• Compressor and poly pig usually used

simultaneously for draining.

• Step 8: Drying operation

• Pig launched (to remove water from the system)

• Pig moved at optimum velocity to remove

maximum volume of contaminants.

• This step repeated until satisfied.


• Step 9: Methanol Cleaning

• Methanol used to improve water draining from pipe.

• This step performed after water draining and drying operation step.

• Below dew point (methanol help combating hydrate formation).

• Methanol filled between two pigs.

• Volume of methanol needed is about 15% of water volume.

• Maximum pipe length is 30 km – depending on methanol availability.

• Methanol must be ensure do not contacted with soil and not be drained to ground (it must be stored in suitable container to be reused)


• Step 19: Air drying

• An alternative to methanol cleaning process

• Can be considered if one of the following

conditions happens:

– Existence of wet gas

– Reasonable cost to replace methanol drying

• Moisture content determined periodically at output

using dew point test (Mirror Hydrometer).

• Satisfied when dew point reach -45oC or lower.


PNEUMATIC TEST

• Usually performed by using compressed air

which relatively low cost.

• In certain condition, for safety reasons, inert

gas (in cylinder) should be considered.


Equipments and Preparation for

the Test 1: Pump and compressor

• Small pipe – using hand pump (however, it takes longer time)

• For bigger pipe, compressor will be used

– Small unit – electric powered (several ft3/min)

– Large unit – diesel engine (150 – 500 ft3/min)

2: Compressed air cylinder

• Using nitrogen gas or compressed air cylinder

• Stored at 2200 psig (15000 kPa)

• Available in several size:

– 70 ft3 (2 m3) to 300 ft3 (8.5 m3)

– The capacity shows the volume at atmospheric pressure.


3: Liquefied Gas Cylinder

• Insulated liquefied nitrogen tank size 100 m3

connected to tanker together with vaporiser.

4: Cylinder System

• Gas or compressed air cylinder easier to be used at

site.

• Cylinder connected to pipeline system.

• The number of cylinder should be determined to

ensure sufficient supply.


5: Number of Cylinder

• Determined using following steps:

a) Calculate volume of pipeline to be tested:

Where;

V : Pipe Volume (ft3 or m3)

d : Pipe Diameter (ft or m)

L : Pipe Length (ft or m)

Lx7854.0xdV 2


b) Determine compressed gas size:

Determined either by physical size or volume

at atmospheric pressure.

Example:

Cylinder : nitrogen gas

Physical size : 1.5 ft3 at 2200 psig

2

1

12

P

PVV

pressurecatmospheriatft

ftV

3

3

2

5.225

73.14

73.1422005.1


c) Identify pressure required

Minimum test pressure can be identified by

referring to code of practice

d) Calculate the number of cylinder required

Following data required:

- Volume of pipeline

- Test pressure

- Cylinder capacity


example

• Calculate the number of gas cylinder required to

perform pneumatic test for the following system:

– Pipeline volume : 175 ft3

– Test pressure : 50 psig

– Cylinder capacity : 1.5 ft3 at 2200 psig


• First nitrogen cylinder connected to the pipeline

2

1

12

V

VPP

psia

pipeftcylinderft

pipeftNftP

42.33

1755.1

1755.22573.14

33

3

2

3

2

2

1

12

P

PVV

3

3

2

4.99

42.33

73.1422005.1

ft

psia

psiapsigftV


• Second nitrogen cylinder connected to the pipeline

2

1

12

V

VPP

2

1

12

P

PVV

psiaP 95.511755.1

1754.9942.332

3

2

94.63

95.51

17522005.1

ft

V


• Third nitrogen cylinder connected to the pipeline

• Therefore, three nitrogen cylinder required.

2

1

12

V

VPP

psigorpsia

P

6.5932.70

1755.1

17594.6395.512


PURGING

• Purging operation should be performed to ensure the

pipeline is free from air before commissioning.

• Any failure to do the operation may lead to incident

such as fire and explosion that will cause loss in

properties and life.

• Purging can be performed through following medium:

– Inert gas (nitrogen or carbon dioxide) for pipe with

diameter of 4 inch or more

– Natural gas can be used for pipe with diameter less

than 4 inch


• Velocity of mixture should be more than methane

flame speed which is 120 ft/min (2 ft/s).

• Usually the operation performed at 200 ft/min at 8

psig at the outlet point.

• This to ensure that, if any spark happens at the

outlet, the flame will not travel inwards the

pipeline.


a) Pipe with diameter less than 4 inch

• Natural gas or nitrogen can used as the medium to

perform the purging operation.

• The procedure are as follows:

Medium: Natural Gas

Check the system layout and note the lower

point, uncontrollable opening and purge point.

Ensure the approval to performed the

operation have been obtained.

Purge point must be more than 0.5 inch


The nearest building located more than 10 feet

and the pipeline safe from any spark supply

Purging velocity at purge pint more than 200

ft/min and 8 psig

Purge point must be monitored

The operation stopped when 100% methane gas

observed at the purge point

For a low pressure system, gas can only be burned

only when purging burner is available.


Medium: Nitrogen Gas

– Calculate number of nitrogen gas cylinder required

– If manifold system used, gas must be flowed until all gas are used

– Pressure at purge point should be maintained at 8 psig and velocity of 200 ft/min

– Manifold system and purge point should be monitored throughout the operation

– The operation stopped when 100% nitrogen


b) Pipe with diameter of 4 inch or more

• Inert gas (nitrogen or carbon dioxide) must be used

• The procedure are as follows:

– Calculate number of nitrogen gas cylinder required

– Manifold system must be used

– Manifold system and purge point should be

monitored throughout the operation

– Pressure at purge point should be maintained at 8

psig and velocity of 200 ft/min

– The system must be gasified after the operation

complete


• Number of nitrogen gas cylinder required

lengthpipexR

lengthpipexDxvolumepipe

2

2

14.3

785.0

013.0xvolumepiperequiredgasnitrogenofnumber

Chap5 Gas Reticulation System

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Transcript of Chap5 Gas Reticulation System