Industry-Standard Gas Flow Calculator
Calculates gas flow rates, depressurization times, purge requirements, and inventory per API 521, ASME B31.8, AGA-8, and NFPA 56 standards. Suitable for preliminary engineering design.
Purge calculations assume ideal mixing. Dead legs require special attention per NFPA 56.
For H₂S service, follow API RP 55 safety procedures.
All calculations for preliminary design only. Verify with licensed professional engineer.
Z-Factor Guide (per AGA-8):
0-200 psig: Z ≈ 0.99 | 200-500 psig: Z ≈ 0.95
500-1000 psig: Z ≈ 0.90 | >1000 psig: Z ≈ 0.85 For accurate Z, use AGA Report No. 8 or Standing-Katz charts
Blowdown Results
Avg. Flow Rate- SCFM
Total Gas Released- SCF
Pressure Drop Rate- psi/min
Choked Flow-
Est. J-T Cooling- °F
Depressurization Time
Time Required- minutes
Volume to Release- SCF
Pipeline Volume
Internal Diameter- in
Volume (ft³)- ft³
Volume (m³)- m³
Volume (gallons)- gal
Volume (barrels)- bbl
Gas Inventory
Gas Type-
Specific Gravity-
Standard Volume- MCF
Mass- lbs
Energy Content- MMBtu
Estimated Value$ -
Purge Requirements
Safety Status-
Final Concentration- %
Volume Changes-
Total Purge Gas- SCF
Est. Total Time- min
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Industry Standards Referenced
API 521 - Pressure-Relieving and Depressuring Systems
ASME B31.8 - Gas Transmission and Distribution Piping Systems
AGA Report No. 8 - Compressibility Factors of Natural Gas
GPA 2172 - Calculation of Gross Heating Value, Relative Density, and Compressibility
NFPA 56 - Standard for Fire and Explosion Prevention During Cleaning and Purging
API RP 55 - Recommended Practice for Conducting Oil and Gas Operations Involving H₂S
ISO 23251 - Petroleum and Natural Gas Industries - Pressure-Relieving Systems