💨 Pressurized Gas Vessel Transient Blowdown Sizer

Size pressurized gas vessel emergency depressurization and blowdown per API 521 / ISO 23251: blowdown duration (min), peak sonic choked mass flow, expansion cooling, and low-temp MDMT brittle fracture risk.

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

Pressurized Gas Vessel Transient Blowdown Sizer

Fluid Mechanics

📊 Solver Telemetry ● ACTIVE

👁️ Views 17

⚡ Solves 14

💾 Downloads 276 📦 Fortran Code 4.5 KB

📅 Released Jun 2026

⏱️ Latency < 1 ms

💨 Pressurized Vessel Emergency Depressurization & Supersonic Flare Jet

Real-time visual simulation: Choked gas release ($M=1$), expanding sonic plume, and auto-cooling vessel wall temperature

📝 Configuration & Presets

🔥 API 521 Separator (15 min) ⚡ Hydrogen 250 bar Vent 🌐 Nitrogen Sphere (50 m³) 🧯 CO2 Cylinder Discharge

🧪 Gas Properties & Vessel Sizing

Pressurized Gas Medium:

Initial Pressure P₀ [bar abs]:

Initial Temperature T₀ [°C]:

Vessel Internal Volume V [m³]:

💥 Blowdown Valve & Target Limits

Blowdown Orifice / Valve ID d_o [mm]:

Discharge Coeff. C_d:

Target Pressure P_target [bar abs]: API 521: 6.9 bar or 50% of design

Flare Header Backpressure [bar abs]:

API 521 Transient Blowdown Formulation:
• Initial Peak Choked Flow: ṁ₀ = C_d · A_o · P₀ · √[ (γ M) / (R T₀) ] · (2/(γ+1))^{(γ+1)/(2(γ−1))}
• Minimum Gas Temperature: T_min = T₀ · (P_target / P₀)^(γ−1)/γ
• Blowdown Duration: t_blow = [ 2 V / ((γ−1) C_d A_o a₀) ] · [ (P₀/P_tgt)^{(γ−1)/(2γ)} − 1 ]
• MDMT Risk: Carbon steel risks brittle fracture below −29°C (ASME Section VIII).

📊 Blowdown Results

📊 Output Summary
💾 Fortran Source

Blowdown Duration to 6.9 bar

3.39 minutes (204 s)

Peak Sonic Flow: 5.86 kg/s | Min Temp: -103.6 °C

HIGH RISK (BELOW -46°C MDMT)

Minimum Fluid Temperature -103.6 °C Expansion cooling limit

Initial Gas Inventory Mass 970.6 kg Volume = 20 m³

Peak Initial Discharge Rate 5.86 kg/s 21.1 Tonnes/h

API 521 Compliance Check PASS (≤ 15 min) Target: 6.9 bar in 15 min

📈 Vessel Pressure P(t) (bar) vs Time (minutes)

📉 Gas Temperature T(t) (°C) vs Time (minutes)

=================================================================
 THERMOFLUIDCALC — PRESSURIZED VESSEL TRANSIENT BLOWDOWN REPORT
=================================================================
Case Title                 : API 521 Gas Plant Separator 15-Minute Blowdown
Gas Medium                 : Methane / Natural Gas (MW = 16.04, γ = 1.31)
Initial Vessel Conditions  : P0 = 75.0 bar abs, Temp T0 = 25.0 C, Volume = 20.00 m3 (Gas Mass = 970.6 kg)
Blowdown Orifice & Valve   : Orifice ID = 30.0 mm, Cd = 0.65, Flare Backpressure = 1.20 bar
-----------------------------------------------------------------
PEAK INITIAL CHOKED FLOW   : 5.865 kg/s (21.11 Tonnes/h)
BLOWDOWN DURATION          : 3.39 minutes (203.6 seconds to 6.9 bar)
MINIMUM FLUID TEMPERATURE  : -103.63 deg C (Isentropic Expansion)
MDMT BRITTLE FRACTURE RISK : HIGH RISK (BELOW -46°C MDMT)
API 521 15-Minute Criterion: COMPLIANT
=================================================================

📘 Calculation Methodology & API 521 Blowdown Standards

API 521 15-Minute Depressurization Rule

In fire emergencies, vessels must be depressurized to $6.9\,\text{bar}$ (or $50\%$ of design pressure) within $15\,\text{minutes}$ to prevent boiling liquid expanding vapor explosions (BLEVE) and vessel rupture.

Low-Temperature Auto-Refrigeration & MDMT

Rapid gas expansion causes extreme adiabatic cooling (Joule-Thomson / isentropic drop). If metal temperature drops below the Minimum Design Metal Temperature (MDMT, e.g. $-29^\circ\text{C}$), carbon steel risks catastrophic brittle fracture.

Key Engineering Assumptions

Choked sonic discharge ($M=1$) across the blowdown restriction orifice.
Isentropic / ideal gas expansion thermodynamics.
Applicable to gas processing separators, LNG storage vessels, and hydrogen fuel trailers.

ThermoFluidCalc Engineering Report