Orifice Flow Β· Restriction Orifice Β· Leak Rate Β· Choked Flow Analysis
Understand leak rate calculations, API 581 hole categories, and emergency response
Enter the upstream pressure, orifice diameter, gas type, and discharge coefficient. The calculator uses compressible flow equations from GPSA Section 17 and API RP 520/521 to determine whether flow is choked (sonic) or subsonic, then calculates the mass and volumetric flow rate.
Choked (sonic) flow occurs when the downstream-to-upstream pressure ratio drops below the critical ratio (approximately 0.53 for natural gas). At choked conditions, the gas velocity at the orifice throat reaches the speed of sound and further reducing downstream pressure does not increase flow rate.
Yes. Use the Calculate Gas Loss Rate mode to find the flow through a known orifice size, or use the Find Equivalent Hole Size mode to back-calculate the orifice diameter needed for a target flow rate. It supports sharp-edged, rounded, nozzle, and short-tube orifice types.
It follows GPSA Engineering Data Book Section 17, API RP 520 Part I, API RP 521, API RP 581 hole size categories, and Crane Technical Paper 410 for compressible gas flow through orifices.