อัปเดต 2026-09-07

Tank Venting

API Standard 2000 (7th ed.)

Sizes an atmospheric/low-pressure storage-tank breather vent or PV valve for the three contingencies API 2000 requires: normal thermal breathing (day/night swing), normal liquid-movement (pump in/out displacement), and emergency fire venting — the vent is sized for the largest of the three.

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Thermal and liquid-movement terms are closed-form power laws in tank volume; fire venting runs the API 2000 piecewise wetted-area heat-input bands, converts the resulting vapor generation rate to an air-equivalent volumetric rate via a √(T/M) similarity scaling, then the orchestrator picks the governing (largest) demand.

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Normal thermal in/out-breathing, API 2000 §3.3.2

V_{I T} = C V^{0.7} R_{i}, V_{O T} = Y V^{0.9} R_{i}

V = tank volume (m³); C = latitude factor (tropical 4 / temperate 5 / polar 6.5); Y = flash-class factor (high-flash 0.32 / low-flash 0.25); R_i = insulation reduction factor. Output directly in Nm³/h of air.

Emergency fire venting — largest wetted-area band, API 2000 §4.3.3.2.2

Q = 4.3 \times 1 0^{8} \cdot F \cdot A_{w s}^{0.82} (A_{w s} \geq 260 m^{2})

Smaller wetted-area bands use different coefficient/exponent pairs (63100·A^1.0, 224200·A^0.566, 630400·A^0.338) and do not credit the environment factor F.

Vapor → air-equivalent conversion, API 2000 §4.3.3.3

V ˙_{ai r} = \frac{m ˙}{ρ _{v a p}} \frac{T / M}{T _{ai r} / M _{ai r}}

ṁ = Q/L (fire heat input ÷ latent heat of vaporization); converts the stored liquid's vapor generation to Nm³/h of air at the 0 °C / 101.325 kPa reference state.

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