API 2000 Tank Vent Sizing Calculator

API 2000 Storage Tank Vent Sizing Calculator

Use this calculator to estimate the required venting capacity for atmospheric storage tanks based on API 2000 7th Edition. Enter your tank parameters below to determine normal inbreathing, normal outbreathing, and emergency venting requirements.

Disclaimer: This calculator provides preliminary estimates for reference only. Actual vent sizing must be performed by a qualified engineer following the complete API 2000 standard, considering all site-specific conditions. Wanan Technology is not liable for decisions based solely on these estimates.

Step 1: Enter Tank Parameters

Step 2: Results

How API 2000 Vent Sizing Works

API 2000 is the primary international standard for atmospheric and low-pressure storage tank venting. It defines three categories of venting requirements:

Normal Inbreathing (Vacuum Protection)

When liquid is pumped out of a tank, the vapor space above the liquid expands and pressure drops. Without adequate venting, this vacuum can cause tank implosion. The total inbreathing requirement is the sum of:

  • Thermal Inbreathing: Caused by temperature drops (day-to-night transition, rainstorm on hot tank roof). API 2000 Table 1 provides values based on tank capacity.
  • Liquid Displacement (Pump-Out): Equal to the maximum pump-out rate converted to air equivalent. API 2000 specifies 5.6 SCFH per GPM (or 0.94 Nm3/h per m3/h) of pump-out capacity.

Normal Outbreathing (Pressure Relief)

When liquid is pumped into a tank or temperature rises, vapor is compressed and pressure increases. The total outbreathing requirement is the sum of:

  • Thermal Outbreathing: Caused by temperature rise. For volatile fluids, API 2000 specifies higher thermal outbreathing than for non-volatile fluids.
  • Liquid Displacement (Pump-In): For volatile fluids, API 2000 specifies 2.0 SCFH per GPM. For non-volatile fluids, 1.0 SCFH per GPM.

Emergency Venting (Fire Exposure)

If a tank is exposed to external fire, the liquid absorbs heat and vaporizes rapidly, creating massive pressure. Emergency venting capacity is calculated based on:

  • Wetted Surface Area: The area of tank shell in contact with liquid up to 30 feet above grade.
  • Environmental Factor (F): 1.0 for uninsulated tanks, 0.3 for insulated tanks, 0 for underground/bunded tanks.
  • Latent Heat & Molecular Weight: Product-specific properties affecting vaporization rate.

Perguntas frequentes

What is API 2000 and which edition should I use?

API 2000 is the American Petroleum Institute standard for venting atmospheric and low-pressure storage tanks. The 7th Edition (2014, reaffirmed 2020) is the current version. It significantly revised thermal inbreathing requirements from the 6th Edition, generally increasing the required capacity. Most jurisdictions and insurance underwriters now require compliance with the 7th Edition.

Do all storage tanks need both normal and emergency venting?

All atmospheric storage tanks require normal venting (inbreathing and outbreathing). Emergency venting is required for tanks storing flammable liquids with flash points below 200 F (93 C) that could be exposed to fire. Tanks storing non-flammable liquids (e.g., water, fire-fighting foam) may not require emergency venting, but local regulations should be checked.

How do I convert SCFH to other flow units?

1 SCFH (Standard Cubic Feet per Hour) = 0.0283 Nm3/h (Normal cubic meters per hour) = 0.0277 m3/h (at actual conditions, approximate). For quick reference: 1,000 SCFH is approximately 28.3 Nm3/h or 16.7 m3/min. This calculator displays results in SCFH; multiply by 0.0283 for Nm3/h.

What size PVRV do I need for my tank?

PVRV sizing depends on the calculated venting capacity, the allowable pressure/vacuum settings, and the valve’s flow coefficient. As a general guide: tanks up to 10,000 bbl typically use 2-inch PVRVs; 10,000-50,000 bbl use 3-4 inch; 50,000-100,000 bbl use 6-8 inch; and larger tanks may require 10-12 inch or multiple PVRVs. This calculator provides preliminary size recommendations, but a detailed flow calculation per API 2000 Appendix B should be performed.

Can I use one PVRV for both normal and emergency venting?

In some cases, yes. If the PVRV’s full-open capacity exceeds both the normal and emergency venting requirements, a single device may suffice. However, for larger tanks or volatile products, the emergency venting requirement is typically much higher than normal venting, requiring a separate emergency relief valve (manway cover type) in addition to the PVRV. Consult API 2000 Section 4.4.5 for combined venting guidance.

How does tank insulation affect venting requirements?

Insulation has two effects: (1) it reduces thermal breathing by buffering temperature changes, though API 2000 still requires full thermal breathing capacity regardless of insulation, and (2) it reduces the emergency venting requirement by lowering the heat input rate during fire exposure. The environmental factor F accounts for this: F=1.0 for bare tanks, F=0.3 for insulated tanks with conductive heat transfer analysis, and F=0 for tanks below grade or behind bunds.

Need a complete tank safety equipment package? Wanan Technology manufactures válvulas de alívio de pressão e vácuo, supressores de chamas, e válvulas de alívio de emergência certified to API 2000, ISO 16852, ATEX, and EAC standards. Our engineers can provide detailed vent sizing calculations and equipment selection for your specific application.