FieldEngineersKitEngineering Reference & ASME Code Basis
1. Core Formula & Variable Definitions
API Standard 2000 7th Edition (2014, Reaffirmed 2020) — Venting Atmospheric and Low-pressure Storage Tanks §3.3 / §3.4 · API Standard 650 — Welded Tanks for Oil Storage (tank class context) · API Standard 620 — Design and Construction of Large, Welded, Low-Pressure Storage Tanks
Vout,liq = 1.01·Vpump-in · Vin,liq = 0.94·Vpump-out
Vout,th = 0.8·V0.9·Clat·Y · Vin,th = 3.0·V0.7·Clat
Q = 43.2·Aw0.82·F · Vemer = (Q/Lv)·√(70.6/M)·1234
API Std 2000 7th Edition (2014/R2020) — free-air Nm³/h screening for API 650/620 class tanks
Normal outbreathing is liquid pump-in displacement plus thermal expansion. Normal inbreathing is liquid pump-out plus thermal contraction. Fire emergency uses wetted lateral area with H_wett ≤ 9.14 m (30 ft). Rates are free-air equivalents for PVRV / hatch screening — not certified OEM selection.
- V (Tank capacity) — Vertical cylinder volume π/4·D²·H (m³ or bbl).
- V_pump-in / out (Max liquid transfer rates) — Maximum filling and emptying rates (m³/h or GPM).
- C_lat (Latitude factor) — 1.0 below 42° latitude; 0.65 at or above 42°.
- Y (Product / volatility factor) — Table 1 class factor on thermal outbreathing — 1.0 for flash point < 37.8 °C; 0.5 for higher flash.
- A_w (Wetted surface area) — π·D·H_wett with H_wett = min(H, 9.14 m / 30 ft).
- F (Environment factor) — 1.0 bare; 0.3 insulated; 0.15 water deluge (screening).
- L_v, M (Latent heat & molecular weight) — Liquid latent heat and vapor MW for emergency air-equivalent rate.
2. Screening rules & default duty
Default metric duty: Ø15 m · H 12 m (≈ 2,121 m³), pump-in 200 m³/h, pump-out 250 m³/h, flash point < 37.8 °C (Y = 1.0), bare F = 1.0, M = 72, L_v = 360 kJ/kg, latitude < 42°. Engine asserts V_out ≈ 991 Nm³/h and V_emer ≈ 21,200 Nm³/h.
Outbreathing 1.01·pump-in and inbreathing 0.94·pump-out (Nm³/h free air per m³/h liquid).
SI thermal out/inbreathing with latitude and Table 1 Y on outbreathing only.
Fire wetted lateral height limited per API 2000 §3.4 for vertical tanks.
Cooling-water ingress, chemical reaction, and heat-exchanger tube rupture gas blow-by need dedicated overpressure design.
Quick Reference Lookup Table
| Case | V_out | V_emergency |
|---|---|---|
| Ø15 m · H 12 m · pump-in 200 · FP < 37.8 °C · F=1.0 | 991 Nm³/h | 21,197 Nm³/h |
| Ø25 m · H 18 m · insulated · FP ≥ 37.8 °C · F=0.3 | 1,930 Nm³/h | 9,526 Nm³/h |
| Ø50 ft · H 40 ft · 1000 GPM · FP < 100 °F · F=1.0 | 37,173 SCFH | 757,244 SCFH |
| Ø80 ft · H 50 ft · insulated · FP ≥ 100 °F · F=0.3 | 57,609 SCFH | 310,244 SCFH |
| Ø15 m · H 12 m · latitude ≥ 42° (C=0.65) | 715 Nm³/h | 21,197 Nm³/h |
| Ø15 m · H 12 m · water deluge F=0.15 | 991 Nm³/h | 3,179 Nm³/h |
Emergency rates use V_emer = (Q/L_v)·√(70.6/M)·1234 with Q = 43.2·A_w^0.82·F. Confirm OEM PVRV / emergency hatch charts before purchase.
3. Applicability & service limits
API 2000 applies to atmospheric and low-pressure metal storage tanks typically in the about −0.5 kPa(g) to 103 kPa(g) design-pressure band with ambient hydrocarbon / chemical liquids. Not for refrigerated cryogenic tanks or high-pressure vessels.
| Group / Regime | Range / Condition | Limit / Criterion | Engineering Notes |
|---|---|---|---|
| Tank class | — | — | Intended for API 650 / API 620 style vertical cylindrical tanks with PVRV or open vents — not ASME VIII pressure vessels as the primary relief path. |
| Design pressure band | — | ≈ −0.5 to 103 kPa(g) | Higher design pressures fall outside API 2000 venting philosophy — use PSV / rupture-disk methods. |
| Fluid service | Ambient / near-ambient liquids | — | Enter site L_v and M. Flash-point class sets Y on thermal outbreathing only. |
| Fire case | — | — | Assumes pool-fire exposure with environment factor F. Drainage, diking, and foam systems are not modeled beyond F. |
Code Applicability & Safety Boundaries
- Screening free-air rates only — not a certified PVRV orifice selection.
- Do not use for thermal shock, runaway reaction, or tube-rupture blow-by without process overpressure analysis.
4. Step-by-Step Worked Example
Field VerificationShowHide
Worked example — Ø15 m · H 12 m · 200 m³/h pump-in
Screen an API 650 vertical tank at 15 m diameter and 12 m shell height with 200 m³/h max fill, 250 m³/h max empty, flash point < 37.8 °C, bare tank, M = 72, L_v = 360 kJ/kg, latitude < 42°.
Liquid movement
Thermal out/inbreathing
Normal totals
Fire emergency
Open /d15m-h12m-pumpin200-metric for the live default case.
5. How to calculate API 2000 tank venting rates
- 1
Enter tank geometry
Set diameter and shell height. Volume is computed as a vertical cylinder.
- 2
Enter transfer rates
Set maximum pump-in and pump-out liquid rates for liquid-movement venting.
- 3
Set fluid and site factors
Choose flash/volatility class (Y), latitude (C), environment F, L_v, and M.
- 4
Read V_out and V_emergency
Hero shows normal outbreathing. Badges show emergency fire venting and normal inbreathing. Size PVRV/hatch to the governing rates.
6. Frequently Asked Questions & Technical References
ShowHide
Liquid pump-in displacement (1.01·V_pump-in) plus thermal expansion outbreathing (0.8·V^0.9·C·Y).
For vertical tanks, A_w = π·D·H_wett with H_wett = min(H, 9.14 m / 30 ft) per API 2000 §3.4.
Fluids with flash point < 37.8 °C (100 °F) or hexane-like class use Y = 1.0 on thermal outbreathing; higher flash uses Y = 0.5 in this screen.
No. Results are free-air screening rates. Confirm OEM PVRV / emergency hatch capacity charts and project specifications.