API 2000 Nitrogen & Fuel Gas Padding
Used to calculate vapor space volume
Auto-fills from product selection; adjust as needed
Typical: 20-40°F/hr for thermal breathing per API 2000
1.0 = standard, increase for desert/tropical locations
Understand API 2000 breathing calculations, inerting vs. padding, regulator selection, and blanket gas system design
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.
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.
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.
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.