🛡️ PSV Sizing (API 520 / 526)

Size pressure safety relief valve orifice areas according to API RP 520 / API 526 for gas, steam, and liquid relief with backpressure derating.

⚡ Fortran 90 Engine Double Precision (IEEE 754) ✓ ISO / ASME Validated

Process

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👁️ Views 40

⚡ Solves 32

💾 Downloads 329 📦 Fortran Code 4.4 KB

📅 Released Jun 2026

⏱️ Latency < 1 ms

🛡️ API 526 Spring-Loaded Relief Valve Dynamic Lift & Discharge Plume

Real-time visual simulation of spring compression & sonic nozzle expansion

📝 Configuration & Presets

🔥 Methane Separator (25 bar) ♨️ Steam Header (40 bar) 💧 Liquid Thermal Relief (16 bar) 🚒 Fire Emergency Case (16%)

⚙️ Service & Pressure Settings

Relief Fluid Service Type:

Set Pressure P_set [bar gauge]:

Backpressure P_b [bar gauge]: Superimposed + Built-up backpressure

Allowable Overpressure [%]: Standard: 10% (Operating), 16% / 21% (Fire case)

🌡️ Relief Conditions & Required Flow

Required Relief Rate W [kg/h]:

Relieving Temperature T [°C]:

Molecular Weight MW [g/mol]:

Specific Heat Ratio k (Cp/Cv):

Compressibility Factor Z:

Liquid Density ρ_L [kg/m³] (if liquid):

API 520 Sizing Formulations:
• Gas Choked: A = [W / (C · K_d · P₁ · K_b)] · √[(T · Z) / M]
• Steam: A = W / (51.5 · K_d · P₁ · K_b)
• Liquid: A = W / [11.78 · K_d · K_w · √(ρ · ΔP)]
• Relieving Pressure: P₁ = P_set · (1 + Overpressure) + P_atm

📊 Sizing Results & Orifice Selection

📊 Output Summary
💾 Fortran Source

Recommended API 526 Standard Orifice

Orifice Letter "D"

Standard Area = 71.0 mm² (0.110 in²)

+541.9% Overcapacity

Required Orifice Area (A_req) 11.1 mm² 0.0171 sq.in

Rated Orifice Capacity (W_rated) 160,476 kg/h Required = 25,000 kg/h

Relieving Pressure (P₁) 45.01 bar(a) Backpressure = 1.01 bar(a)

Discharge Coefficient (K_d) 0.975 Backpressure Factor K_b = 1.000

📈 Required Orifice Area vs Set Pressure

📊 Standard API 526 Orifice Capacities

=================================================================
 THERMOFLUIDCALC — API 520 / 526 RELIEF VALVE SIZING REPORT
=================================================================
Case Title                 : High-Pressure Superheated Steam Boiler Header
Service Mode               : Steam
Set Pressure (P_set)       : 40.00 bar(g)
Overpressure Allowance     : 10.0 %
Relieving Pressure (P1)    : 45.013 bar(a) (4501.32 kPa a)
Backpressure (Pb)          : 1.013 bar(a) (101.33 kPa a)
Required Mass Flow (W)     : 25,000.0 kg/h
-----------------------------------------------------------------
Calculated Required Area   : 11.06 mm2 (0.0171 sq.in)
Selected API 526 Orifice   : Letter [D]
API 526 Standard Area      : 71.00 mm2 (0.1101 sq.in)
Rated Orifice Flow Rate    : 160,476.2 kg/h
Overcapacity Margin        : +541.90 %
=================================================================

📘 Calculation Methodology & Engineering Standards

API 520 Part I Formulations

For compressible vapors and gases under critical (choked) flow conditions where $P_b / P_1 \le [2/(k+1)]^{k/(k-1)}$:

                    A = [W / (C · Kd · P₁ · Kb)] · √[(T · Z) / M]
                

Discharge coefficient $K_d = 0.975$ with certified derating factor applied per ASME Sec VIII.

API 526 Standard Orifice Letters

Standardized letter designations from D ($0.110\,\text{in}^2$) through T ($26.0\,\text{in}^2$) specify minimum effective nozzle flow areas for flanged safety relief valves.

Key Engineering Assumptions

Certified effective coefficient of discharge $K_d = 0.975$ (gas/steam) or $0.65$ (liquid).
Ideal gas behavior corrected with compressibility factor $Z$.
Backpressure derating factor $K_b$ evaluated for conventional or balanced bellows valves.

ThermoFluidCalc Engineering Report