API 2000 Normal Venting Calculator v2 | In the Heat of Process

Input Data

Sections 3.3.2.2 – 3.3.2.4

Location

Latitude Table 1 & 2 ?

Tank Volume

Tank volume V_tk Eq. 7–10 ?

m³

Calculate from geometry

Orientation

Head Type

Inner diameter D ?

Shell length L ?

Head depth a

For vertical cylindrical tanks, volume based on shell height is acceptable (§3.3.2.3.1).

Insulation & Wall Construction

R_i reduces thermal inbreathing (Eq. 9) and thermal out-breathing (Eq. 7). No insulation = R_i = 1.0.

Tank is insulated?

Insulation type

Insulation material properties

R_in = 1 / (1 + h·l_in/λ_in) [Eq. 11]

Thickness l_in ?

Conductivity λ_in ?

W/m·K

Inside HTC h ?

W/m²·K

Double wall tank?

Double Wall Eq. 13

% surface outside containment ?

R_c = 0.25 + 0.75·(A_c/A) [Eq.13]

Liquid Discharge Eq. 5

V̇_ip = V̇_pe [Eq. 5] — direct, no correction needed

Max discharge rate V̇_pe Eq. 5 ?

m³/h

Operating temperature ?

°C

Thermal Inbreathing Eq. 9

V̇_IT = C · V_tk^0.7 · R_i [Eq. 9]

Vapor pressure condition Table 2 ?

Liquid Filling Eq. 1 / 3

Non-volatile (Vp ≤ 5 kPa): V̇_op = V̇_pf [Eq. 1] Volatile (Vp > 5 kPa): V̇_op = 2.0 · V̇_pf [Eq. 3]

Max filling rate V̇_pf Eq. 1/3 ?

m³/h

Liquid volatility §3.3.2.2.1 ?

Operating temperature ?

°C

Flashing liquid (§3.3.2.2.1c): If the entering liquid flashes upon entering the tank, perform a separate equilibrium flash calculation and add the resulting vapor generation to the out-breathing requirement. No simplified formula is provided in API 2000 for this case.

Thermal Out-breathing Eq. 7

V̇_OT = Y · V_tk^0.9 · R_i [Eq. 7]

Y-factor Table 1 ?

—

Y-factor is set automatically from your latitude selection. Table 1: <42° → 0.32 · 42–58° → 0.25 · >58° → 0.20

Method Selection §3.3.3.3.3

§3.3.3.3.3: Where the stored fluid's properties are similar to hexane, the required venting capacity can be read directly from Table 5/Table 7 (A_TWS < 260 m²) or Eq. 16 (A_TWS ≥ 260 m², P > 7 kPa) — no need to evaluate L, T, or M individually. For diesel or other fluids that differ meaningfully from hexane (e.g. much higher latent heat, different molecular mass), use the general Eq. 14 route instead.

Wetted Surface & Heat Input Table 3

q = 906.6 · (Q·F/L) · (T/M)^0.5 [Eq. 14]

Wetted surface area A_TWS Table 5 ?

m²

Design pressure ?

kPa(g)

Calculate A_TWS from tank geometry

Tank configuration Table 5 note a

A_TWS = πD · min(H, 9.14) — excludes roof & bottom plate

Diameter D ?

Shell height H ?

Table 3 — Heat Input Q (SI): <18.6 m² → 63,150·A_TWS · 18.6–93 m² → 224,200·A_TWS^0.566 · 93–260 m² → 630,400·A_TWS^0.338 · ≥260 m² & P>7 kPa → 43,200·A_TWS^0.82 · ≥260 m² & P≤7 kPa → 4,129,700 W (capped — §3.3.3.3.3 / Annex B).

Environmental Factor Table 9

Tank design/configuration ?

F-factor ?

—

Only one environmental factor may be credited (§3.3.3.3.4). Insulation must resist dislodgment by fire-fighting equipment and not decompose below 537.8 °C (1000 °F) — Table 9 note a.

Vapor Properties at Relieving Conditions Eq. 14

Latent heat of vaporization L ?

J/kg

Relieving vapor temperature T ?

°C

Relative molecular mass M ?

—

Defaults shown (334,900 J/kg, 15.6 °C, M=86.17) are hexane at atmospheric pressure. For diesel, typical relieving-condition values are much higher latent heat (~250,000–260,000 J/kg) and higher molecular mass (~170–200) — replace with your own fluid data at relieving conditions.

Hexane-similar Route Table 5 / Table 7 / Eq. 16

A_TWS < 260 m²: read from Table 7 • A_TWS ≥ 260 m², P ≤ 7 kPa(g): fixed 19,910 Nm³/h • A_TWS ≥ 260 m², P > 7 kPa(g): q = 208.2·F·A_TWS^0.82 [Eq. 16]

This route assumes the reference fluid (hexane: L=334,900 J/kg, M=86.17, T=15.6 °C) and applies only the environmental factor F from Table 9 above. No latent heat, temperature, or molecular-mass entry is needed.

Results

§3.3.1 Summary

Enter data and press Calculate.

Quick Reference

Tables 1 & 2

Y-factor — Table 1

Latitude	Y

C-factor — Table 2

Lat.	Hex<25°C	Hex≥25°C	Higher

"Higher/unknown" C-factor applies when vapor pressure > hexane or is unknown, regardless of temperature.