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CHOOSING A LINE SIZE AND WALL THICKNESS
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LESSON OUTCOMES
At the end of todays lecture, students shouldbe able to:
Describe effect of velocity to size liquid, gas andtwo-phase pipelineDetermine ID using velocity equationsDescribe standards and requirements used to
calculate wall thickness of pipeDetermine wall thickness of pipe using standards.
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LECTURE OUTLINE
Selection criteriaLine size criteria focus on VELOCITY
Wall thickness criteriaExample
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SELECTION CRITERIA
TWO-PHASE LINE
LIQUID LINES
GAS LINES
VELOCITY PRESSURE DROP
LINE SIZE
ANSI B 31.1 ANSI B 31.3 ANSI B 31.4
LOCATION CLASS1,2,3 AND 4
TEMP DERATING
FACTOR,T
DESIGN FACTOR,F
ANSI B 31.8
STANDARDS ANDREQUIREMENTS
WALL THICKNESS
SELECTION CRITERIA
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LINE SIZE CRITERIA
PRESSURE DROPImportant for long flowlineImportant for flowline between equipment operatingat the same or nearly the same pressure
Equivalent length and elevation changes to beconsidered
VELOCITY
Below maximum to prevent erosion, noise or waterhammer Above minimum to minimize surging and transportingsand or solid particles
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LINE SIZE CRITERIA (contd..)
Erosional Flow
Liquid droplets impact the wall with enough forceto erode the metal and exposing it to the fluidand allowing more corrosion to occur
Fluid erosion occurs when V > 21)( m
e
C V
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LINE SIZE CRITERIA (contd..)
LIQUID LINEGAS LINE
Max velocity 15 ft/s and min velocity is3 ft/s
Sized to maintain avelocity sufficient tokeep solid particlesfrom depositing
Fluid velocity in oilfieldunit:
Max velocity 60-80 ft/s and min velocity is
10-15 ft/s Sized to minimize liquid
settling out and effect ofnoise and corrosion
Pressure less than 1000psi, erosional velocity isnot significant
Gas velocity in oilfieldunit:
VELOCITY
2
1012.0d Q
V P d
TZ QV g 260
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Standards and Requirement
ANSI B 31.3 - Power Piping.This standard deals with steam and is required by the U.S Coast Guard onall rigs
ANSI B 31.3 Chemical Plant and Petroleum Refinery Piping.This standard is required by the US Minerals Management Service foroffshore platform in federal, state waters and offshore facilities in otherparts of the world
ANSI B 31.4 Liquid Petroleum Transportation Piping System.This standard is normally used in onshore oil production facilities
ANSI B 31.8 Gas Transmission and Distribution Piping System.This standard is normally used for gas lines in onshore productionfacilities and when transporting or distributing gas.
WALL THICKNESS CRITERIA
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General Hoop Stress Formula for ThinWall Cylinders
WALL THICKNESS CRITERIA
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WALL THICKNESS CRITERIA (contd..)
ANSI B 31.3
Tol PY SE
Pd t t t o
thc
100
100
)(2
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WALL THICKNESS CRITERIA (contd..)
ANSI B 31.8
)(2 FETS Pd
t o
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STEPS TO CHOOSE A LINE SIZE AND WALLTHICKNESS
i. Determine the max and min velocityallowable for specific fluid types
ii. Find pressure drop of the systemiii. Determine the I.D of pipe relative to the
velocityiv. Determine pressure drop in the pipeline
v. Find the wall thickness based on thestandard vi. Choose the appropriate pipeline size from
the standard
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EXAMPLE CALCULATION
A gas with specific gravity of 0.85, viscosity of 3 cp and compressibilityfactor of 0.67 flows at a rate of 23 MMscfd in a pipeline.
The pipeline is laid at Gobi Desert.
The inlet pressure of the gas is 900 psi at a temperature of 80 oF.
The length of the pipeline is 7000 ft.The gas flows to a dehydrator that operates at 800 psi. The rated pressure ofthe pipeline is 1480 psi. The pipe is seamless and the minimum yieldstrength is 35000 psi.
Determine the appropriate line size and wall thickness based on ANSI B 31.8