What is tank blanketing gas?

Tank blanketing (also called tank padding or inerting) is the practice of maintaining a low-pressure blanket of inert gas (typically nitrogen or fuel gas) in the vapor space of atmospheric storage tanks. This prevents oxygen ingress which reduces fire/explosion risk, minimizes product oxidation, and reduces evaporative losses. Blanket gas pressure is typically maintained at 0.5-1.0 oz/in2 above atmospheric.

How is blanket gas demand calculated per API 2000?

API 2000 defines two components of blanket gas demand: (1) Liquid movement inbreathing - gas required to replace liquid volume as the tank is emptied, calculated as emptying rate x 5.615 ft3/bbl; (2) Thermal inbreathing - gas required to compensate for vapor space contraction during cooling, based on tank capacity and temperature swing rate from API 2000 Table 2. Total demand is the sum of both components.

What blanket gas pressure should I use?

Typical blanket gas set pressure is 0.5 oz/in2 (approximately 0.87 in.WC or 0.031 psig). Tank design pressure is usually 1.0 oz/in2 and design vacuum is 0.5 oz/in2 for atmospheric tanks per API 650. The blanket gas regulator must be set below tank design pressure with adequate margin for lock-up pressure.

When should I use nitrogen vs natural gas for blanketing?

Nitrogen is preferred when the stored product is reactive (NGL, chemicals), when a truly inert atmosphere is required, or when the tank is near ignition sources. Natural gas is more common in upstream/midstream operations where it is readily available and cost-effective. CO2 is used for specific applications like wine or food-grade storage. NFPA 69 provides guidance on inerting requirements.

Tank Blanketing Gas Calculator | Nitrogen & Fuel Gas Padding (API 2000)

Tank Dimensions

Tank Diameter

Tank Height (Shell)

Normal Liquid Level

Used to calculate vapor space volume

Stored Product

Product Type

Product Flash Point

°F

Auto-fills from product selection; adjust as needed

Tank Insulation

Liquid Movement Rates

Maximum Filling Rate

Maximum Emptying Rate

Blanket Gas Properties

Blanket Gas Type

Blanket Gas Set Pressure

Blanket Gas Cost

$/MSCF

Tank Design Parameters

Tank Design Pressure

oz/in²

Tank Design Vacuum

oz/in²

Environmental Conditions

Maximum Ambient Temp Swing Rate

°F/hr

Typical: 20-40°F/hr for thermal breathing per API 2000

Solar Radiation Factor

1.0 = standard, increase for desert/tropical locations

Understanding Tank Blanketing

Why Blanket Gas?
Prevents oxygen ingress into tank vapor space, reducing fire risk, product oxidation, and emissions. Required for flammable liquids per NFPA 69 and API 2521.

Breathing Sources:
Liquid movement (filling/emptying displaces vapor), thermal breathing (temperature changes cause vapor expansion/contraction), and losses through fittings.

Typical Applications:
Crude oil tanks, condensate storage, produced water tanks, chemical storage, NGL bullets, methanol tanks, and any vessel storing volatile or oxygen-sensitive products.

Learn the Theory

Understand API 2000 breathing calculations, inerting vs. padding, regulator selection, and blanket gas system design

Read Engineering Guide →

Results

Total Inbreathing (Blanket Gas Demand)

SCFH

Liquid Movement Inbreathing -

Thermal Inbreathing -

Total Outbreathing -

Liquid Movement Outbreathing -

Thermal Outbreathing -

Emergency Venting Rate (Fire) -

Vapor Space Volume -

Tank Total Capacity -

Blanket Gas Regulator Cv -

Vent Valve Size Required -

Annual Gas Consumption -

Annual Blanket Gas Cost -

Key Formulas

Q_in = Q_empty + Q_thermal

Q_in = Total inbreathing demand (SCFH)

Q_empty = Emptying rate × 5.615 ft³/bbl

Q_thermal = API 2000 Table 2 factor × capacity

Q_fire = C × A_wetted^0.82 (emergency)

Cv = Q / (963 × √ΔP) for gas

Standards & References

API 2000 (7th Ed., 2014)
Venting Atmospheric and Low-Pressure Storage Tanks
API 2521
Use of Pressure-Vacuum Vent Valves for Atmospheric Pressure Tanks
NFPA 69
Standard on Explosion Prevention Systems
API 650
Welded Tanks for Oil Storage
GPSA Engineering Data Book
Section 7: Separation Equipment

Engineering Notes

Blanket pressure: Typical 0.5 oz/in² (0.031 psig); must be below tank design pressure
API 2000 Tables: Thermal breathing factors based on tank total capacity and insulation status
Emergency venting: Fire case per API 2000 Clause 5.4 using wetted area
Multiple regulators: Tanks >100 ft diameter may need parallel regulators
Nitrogen purity: 95-99.5% N2 typical; high purity for chemical storage
Gas consumption: Estimate includes continuous losses through fittings (20% safety factor)

Quick Reference

1 oz/in² = 1.732 in.WC = 0.0625 psig
1 BPH = 5.615 ft³/hr liquid displacement
1 GPM = 8.021 ft³/hr
Standard conditions: 60°F, 14.696 psia
N2 specific gravity = 0.967 (vs air)

Tank Blanketing Gas Calculator