Oil/Gas Pipelines

Facilities Engineering, Transportation and Storage

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W. K-S. Pao

1. Identify suitable techniques and equipment for petroleum productionand export facilities design and optimisation

2. Apply cost estimating methods for project feasibility study to analyseproject economics

3. Apply risk/reliability assessment in equipment design and selection

Course Outcome

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4. Design the pipeline and storage system

Where Are We in the Big Picture?

Separator

Oil Gas Water

piping

pump Compressor pump

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Oil/Gas

Terminal

Storage

Sales

Venting

Flaring

Treatment

Injection

Meter

Gas Flow in Pipes

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Pipeline Equations

•• WeymouthWeymouth•• PanhandlePanhandle•• ModifiedModified PanhandlePanhandle

UsingUsing thesethese threethree equations,equations, variousvarious combinationcombination ofof pipepipediameterdiameter andand wallwall thicknessthickness forfor aa desireddesired raterate ofof fluidfluid

throughputthroughput cancan bebe calculatedcalculated

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throughputthroughput cancan bebe calculatedcalculated

Pipeline Equations

••WeymouthWeymouth equationequation isis preferredpreferred forfor smallersmaller--diameterdiameter lineslines((DD << 1515 inin))..

••PanhandlePanhandle equationequation andand thethe ModifiedModified PanhandlePanhandle equationequation arearebetterbetter forfor largerlarger--sizedsized lineslines..

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Weymouth Equation for Horizontal Flow

• Weymouth proposed that f vary as a function ofdiameter in inches as follows:

where q = scfh

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where qh = scfh

D = pipe internal diameter, in f = Moody friction factor

••WeymouthWeymouth equationequation isis preferredpreferred forfor smallersmaller--diameterdiameter lineslines ((DD << 1515 inin))•• ForFor partiallypartially developeddeveloped flowflow regimeregime

Weymouth Equation for Horizontal Flow

• Assumptions for use of the Weymouth equation including

• no mechanical work,

• steady flow,

• isothermal flow,

• Constant compressibility factor,

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• Constant compressibility factor,

• horizontal flow,

• and no kinetic energy change.

• These assumptions can affect accuracy of calculationresults.

Example 1

For the following data given for a horizontal pipeline, predict gas flow rate in ft3/hr

through the pipeline given Z=0.9188 and viscosity 0.0099cp.

Solution[ ] [ ] 459.67R F= +

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[ ] [ ] 459.67

1' 12"

R F= +

=

For the following data given for a horizontal pipeline, predict gas flow rate in ft3/hr through the pipeline by using Weymouth.

Diameter of pipeline = 16 inLength = 220 miles

Average temperature = 80 deg FSpecific gravity of gas = 0.7

Upstream pressure = 650-psia

Downstream pressure = 230-psia

Exercise 1

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Downstream pressure = 230-psiaAbsolute roughness of pipe= 0.0006-in

Standard temperature = 60 deg F

Standard pressure = 14.7 psiaAverage z factor = 0.8533

Viscosity of gas = 0.0099

Ans: ~2.4 MMscf/hr

Panhandle A Equation-Horizontal Flow

pipeline flow equation is thus

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where q is the gas flow rate in ft3/d measured at Tb and pb,and other terms are the same as in the Weymouth equation.

Panhandle B Equation-Horizontal Flow

(Modified Panhandle)

Long transmission and Delivery lines

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q = gas flow rate (ft3/d)

Units are same as in Panhandle A Eqn

Panhandle B Equation-Horizontal Flow

(Modified Panhandle)

A section of a pipeline system is to handle 200 MMSCFD gas flow. The pipeline inlet pressure is 900 psig and the gas flows to a dehydrator operating at 800 psig.

The allowable working pressure of the pipeline is 1480 psi. The following data are given: STC 14.73 psi, 60oF, average temperature 80oF, compressibility 0.67,

specific gravity of gas 0.85, viscosity 0.01 cp, length 5 miles. Determine D.

Soln:

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( )0.510

2 21.02

6 2.530

0.961

914 814520200 10 737

14.73 (540)(0.67)(5)(0.85)D

− × =

Example

A natural gas pipeline, NPS 16, 0.25”, 50 mi long, with a branch pipe (NPS 8,

0.25”, 15 mi long), as shown in Figure below, is used to transport 100 MMSCFD gas (gravity = 0.6, viscosity 0.000008 lb/ft-s) from A to B (20 mi long). At B, a delivery of 30 MMSCFD occurs into the branch pipe BE. The delivery pressure at

E must be maintained at 300 psig. The remaining volume 70 MMSCFD is shipped to terminal C at the delivery pressure of 600 psig. Assume a constant gas temperature of 60F, pipeline efficiency of 0.95, base temperature and pressure at

60F and 14.7 respectively. The compressibility factor Z=0.88.

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Cont.

a) Using Panhandle A, calculate the inlet pressure at Ab) Is a pressure regulator required at E?

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Cont.

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Cont.

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Empirical Pipeline Equation

A general non-iterative pipeline flow equation is written as

[ft3/day]

The values of the constants are given in Table for the different

pipeline flow equations.

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pipeline flow equations.

Plant Piping – Low Pressure Flow

Short run of gas piping < 100 psi

=∆

5

2000336.0

100

d

fWP

m

ρ

W, Rate of flow, (1000 Ib/hr)

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1 2

100 1

m

2

2 9

5

(10 ) ; where C

336,000f and C

d

or

C C WP

ρ ρ

−

∆ = =

=

The solution is a pressure gradient in psi/100 ft

Operationally...

Rate of flow, W

(1000 Ib/hr)

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Example

Calculate the pressure drop in a 10-in.,Schedule 40 pipe for a flow of 150,000 Ib/hr of

methane. Temperature is 60°F and pressure is 750 psia. The compressibility factor is

0.905

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3(16.042)(750)2.38lb/ft

(10.73)(460 60)(0.905)

Mp

RTzρ = = =

+

Example

C1 = 22.5

C2 = 0.0447

∆P = 22.5(0.0447)/2.38

=0.423 psi/100 ft

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Example

Calculate the required line size (of Schedule 40 pipe)to give ∆P100 = 1 psi or less when

flowing 75,000 lb/hr of methane at 400 psia and 100°F. The compressibility factor is

0.96

C1 = 5.6

3(16.042)(400)1.11lb/ft

(10.73)(460 100)(0.96)

Mp

RTzρ = = =

+

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C1 = 5.6

C2 = (∆P100)ρ/C1

= 1(1.11)/5.6 = 0.2

Example

The smallest size of Schedule 40 pipe with C2 less than

0.20 is 8-in pipe.

For 8-in. Sch 40 pipe, C2 is 0.146. The actual pressure drop

can then be calculated as

∆P = 5.6(0.146)/1.11 = 0.74 psi/100ft

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