Gas Pipeline Blowdown – Semiemperical Model – Report No. 87-2

Based on SW Research Report calculations for the blowdown time and mass of gas vented to atmosphere to a piping system. Accurate to within a few percent.
Blowdown time is impacted through constricting valve changes from sonic (choked) flow to subsonic. This is because of the pressure ratio across the valve is unknown.
PTLB Testing 2.4_Intro.png
Where
π‘‰π‘œΒ βˆ’ Total Volume[ft3]
π‘‰π‘ π‘¦π‘ Β βˆ’ Volume of system[ft3]

 
 

 
PTLB Testing 2.4_Intro 2.png

π‘‰π‘ƒΒ βˆ’ Volume of Mainline Pipe[ft3]
πΏπ‘Β βˆ’ Mainline Pipe Length[in]
π·π‘π‘–Β βˆ’ Mainline Pipe Internal Diameter[in]

 

 
PTLB Testing 2.4_Intro 3 Revised.png

𝑉𝑠(𝑖)Β βˆ’ Volume of individual pipes[ft3]
𝐷𝑠(𝑖)Β βˆ’ Diameter of individual pipes[in]
𝑀𝑑𝑠(𝑖)Β βˆ’ Wall Thickness of individual pipes[in]
𝐿𝑠(𝑖)Β βˆ’ Length of individual pipes[mi]

 

 
PTLB Testing 2.4_Intro 4.png

π‘“Β βˆ’ Friction Factor(Sum of flow friction through all diameters of blowdown piping)
πΏΒ βˆ’ Blowdown Pipe Length[ft]
π‘‘π‘–Β βˆ’ Internal Diameter of Blowdown Pipe[in]

 

 
PTLB Testing 2.4_Intro 5.png

π΄π‘ŸΒ βˆ’ Crossβˆ’Sectional Area of Choke[in2]
π·π‘ŸΒ βˆ’ Diameter of Choked Flow Point[in]

 

 
PTLB Testing 2.4_Intro 6.png

π΄π‘Β βˆ’ Crossβˆ’Sectional Area of Blowdown Pipe[in2]
π‘‘π‘–Β βˆ’ Internal Diameter of Blowdown Pipe[in]

 
PTLB Testing 2.4_Intro 7.png

π‘…π΄Β βˆ’ Ratio of Choked Flow Area to Pipe Flow Area
π‘π‘“Β βˆ’ Coefficient of Blowdown Loss(Sum of loss for 𝑅𝐴/𝑓𝑙𝑑)

 

 

 
PTLB Testing 2.4_Intro 8.png
 

π‘ƒπ‘ π‘–Β βˆ’ Initial Subsonic Pressure[psi]
π‘ƒπ‘–π‘›Β βˆ’ Initial Pressure[psi]
π‘ƒπ‘“Β βˆ’ Final Pressure[psi]
π‘ƒπ‘Β βˆ’ Base Pressure[psi]
π‘ƒπ‘π‘Žπ‘£π‘”Β βˆ’ Average Sonic Pressure[psi]
π‘ƒπ‘ π‘Žπ‘£π‘”Β βˆ’ Average Subsonic Pressure[psi]

 

 
From the SWRI – SIMPLIFIED BLOWDOWN CALCULATIONS FOR PRESSURIZED GAS SYSTEMS Technical Report you can find tables and equations to complete many of the remaining calculations in this module.
PTLB Testing 2.4_Intro 9.png

π›ΎΒ βˆ’ Can be found in table I of the SWRI Technical report mentioned above.
π‘…Β βˆ’ Universal gas constant (π‘ˆπ‘ŸΒ = 1545)divided by the molecular weight 𝑀𝑀
π΄π‘Β βˆ’ Acoustic Velocity[ft/sec]
π΄π‘π‘Β βˆ’ Sonic Acoustic Velocity[ft/sec]
π΄π‘π‘ Β βˆ’ Subsonic Acoustic Velocity[ft/sec]
π‘”Β βˆ’ gravitational constant, 32.2
π‘Β βˆ’ Compressibility Factor
π‘‡Β βˆ’ Absolute Temperature of the gas[Β°R]

 
 
PTLB Testing 2.4_Intro 10.png
π‘π‘’Β βˆ’ Isentropic Compression Exponent
 

 

PTLB Testing 2.4_Intro 11.png
𝑀𝑒𝑐 &Β π‘€π‘’π‘ Β βˆ’ Thermodynamic multiplier to account for compressibility, Table II(choked and subsonic)

 

 
PTLB Testing 2.4_Intro 12.png
π‘‡π‘Β βˆ’ Choked Blowdown Time[sec]

 
 
 
PTLB Testing 2.4_Intro 13.png
π‘‡π‘ Β βˆ’ Subsonic Blowdown Time[sec]
 

 

 
PTLB Testing 2.4_Intro 14.png
π‘‡π‘‡π‘œπ‘‘π‘Žπ‘™Β βˆ’ Total Blowdown Time[min]
 

 

 
PTLB Testing 2.4_Intro 15.png

βˆ†π‘€π‘Β βˆ’ Mass Loss[lbs]
π‘‰πΏπ‘œπ‘ π‘ Β βˆ’ Gas Volume Lost[MSCF]

 

 

Input Parameters

  1. To create a new case, click the β€œAdd Case” button
  2. Select the Gas Pipeline Blowdown – Semiempirical Model – Report No. 87-2 application from the Pipeline Testing module.
  3. Enter Case Name, Location, Date and any necessary notes.
  4. Fill out all required fields.
  5. Make sure the values you are inputting are in the correct units.
  6. Click the CALCULATE button.

  • Pb – Base Pressure(psia)
  • Pi – Initial Pressure(psig)
  • Pf – Final Pressure(psig)
  • Lo – Main Line Pipe Length(ft)
  • do – Main Line Pipe Internal Diameter(in)
  • L – Blowdown Pipe Length(ft)
  • d – Internal Diameter of Blowdown(in)
  • dr – Diameter at Choke Flow Point(in)

PTLB Testing 2.4_Input.png
PTLB Testing 2.4_Input 2.png
 

Outputs/Reports

  1. View the results.
  2. If an input parameter needs to be edited be sure to hit the CALCULATE button after the change.
  3. To SAVE, fill out all required case details then click the SAVE button.
  4. To rename an existing file, click the SAVE As button. Provide all case info then click SAVE.
  5. To generate a REPORT, click the REPORT button.
  6. The user may export the Case/Report by clicking the Export to Excel/PowerPoint icon.
  7. To delete a case, click the DELETE icon near the top of the widget.

PTLB Testing 2.4_Output.png

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Table of Contents
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  3. API Inspector's Toolbox
  4. Horizontal Directional Drilling PowerTool
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  6. Hydrotest PowerTool
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