Flare Tip Velocity & API 521 Mach Number Calculator
Calculate flare tip exit velocity, Mach number, and regulatory compliance limits per API 521 and EPA 40 CFR 60.18 to ensure flame stability and prevent blow-off.
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Flare Tip Exit Velocity & Compliance
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Frequently Asked Questions
What are the API 521 Mach number limits for flare tips?
For continuous normal process flaring, API 521 recommends a maximum tip velocity of 0.20 Mach to limit noise and minimize mechanical wear on the flare tip. For emergency peak flaring cases, velocities up to 0.50 Mach are standard, provided pressure drop and noise are acceptable.
What is the EPA 40 CFR 60.18 regulation on flare velocity?
The US EPA regulates industrial flares to ensure at least 98% VOC destruction efficiency. Under 40 CFR 60.18, flares must operate with a continuous pilot, satisfy minimum heating values (≥300 BTU/scf for steam-assisted flares), and strictly remain below calculated maximum exit velocity limits (Vmax up to 400 ft/s).
What occurs if flare tip velocity is too high or too low?
Excessive velocity causes flame blow-off, where the flame detaches from the tip and blows out, releasing raw unburned VOCs into the atmosphere. Insufficient velocity (< 3 to 5 ft/s) allows low-heat flames to burn back into the interior of the burner tip, rapidly melting flare tip metallurgy.