Calculators›Flare Backpressure
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Flare Backpressure Calculator

Calculate flare header backpressure, pressure drop, and tip velocity, per API 521.

API 520API 521
Flare System Backpressure Calculator
Evaluates built-up backpressure in flare headers and its effect on pressure relief valve capacity. Ensures compliance with API 521 backpressure limits (10% conventional, 50% balanced, 70% pilot-operated) and calculates the Kb capacity correction factor per API 520.

Pipe Geometry & Flow Parameters

lb/hr
in
ft
count
count
count
count
Fittings use L/D ratios per Crane TP-410

Gas Properties

g/mol
°F
vel. heads
Backpressure is solved forward from the flare-tip atmospheric discharge — typical tip K ≈ 1.5–3.0 (vendor data).
-
Cp/Cv
cP
Typical natural gas: μ = 0.01-0.015 cP at operating conditions

Relief Valve Parameters

psig
lb/hr
Valve Type Limits:
• Conventional: Max 10% backpressure (normal)
• Balanced Bellows: Max 50% backpressure
• Pilot Operated: Max 70% backpressure

📚 Learn the Theory

Learn API 521 backpressure limits, relief valve capacity, and network analysis

Read Engineering Guide →

About This Calculator

Analyzes built-up backpressure in flare headers and its impact on relief valve capacity per API RP 520/521.

Standards Applied:

  • API 520: Kb correction factors (Figs. 30, 31)
  • API 521: Backpressure limits by valve type
  • Crane TP-410: L/D method for fittings

Key Outputs:

  • Mach Number: Keep < 0.5 per API 521
  • Kb Factor: Capacity correction for backpressure
  • Compliance: Pass/fail vs. valve type limits

Frequently Asked Questions

What does the Flare Backpressure Analysis tool calculate?

It calculates flare header backpressure, header sizing, pressure drop, and tip velocity to ensure relief valve performance per API 521.

Why is flare backpressure analysis important?

Excessive backpressure in flare headers can reduce relief valve capacity, potentially causing overpressure in protected equipment.

What standard governs flare backpressure requirements?

API 521 specifies backpressure limits for flare systems to ensure proper relief valve performance.

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