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API TR 2567-2005: A Technical Guide to Evaporative Loss Estimation from Fixed-Roof Tanks
Understand the methodology, application, and compliance aspects of this essential petroleum industry technical report
API TR 2567-2005 (originally published as API 2567) is a technical report developed by the American Petroleum Institute (API) to provide standardized methods for estimating evaporative losses from fixed-roof storage tanks in the petroleum and petrochemical industry. This document serves as a critical resource for environmental engineers, facility operators, and regulators seeking to accurately quantify fugitive emissions of volatile organic compounds (VOCs) and other hydrocarbons.
Scope and Purpose
The primary scope of API TR 2567-2005 includes the calculation of total evaporative losses from fixed-roof tanks, which consist of two main components:
- Standing storage loss: Evaporation that occurs due to daily temperature and pressure changes in the tank vapor space when no liquid level change occurs.
- Working loss: Evaporation caused by the displacement of vapor during filling operations, as well as additional evaporation caused by the increased surface area during emptying.
The report applies to hydrocarbons with vapor pressures in the range typical of crude oil, gasoline, and other refined petroleum products stored at atmospheric pressure. It covers both vertical and horizontal fixed-roof tanks with various roof designs (cone, dome, and flat roofs).
Key Insight: API TR 2567-2005 is intended for use in emission inventories, permit applications, and regulatory reporting. Its methodology is also referenced in the U.S. EPA’s AP-42 Compilation of Air Pollutant Emission Factors (Chapter 7: Liquid Storage Tanks).
Technical Requirements and Loss Estimation Methods
The core of API TR 2567-2005 presents deterministic equations and empirical factors for calculating annual evaporative losses. A comprehensive table of key parameters is provided below.
| Parameter | Symbol | Units | Description |
|---|---|---|---|
| Tank diameter | D | ft (m) | Inner diameter of the fixed-roof tank |
| Vapor space volume | Vv | ft³ (m³) | Volume of vapor space above liquid (varies with liquid level) |
| Vapor pressure of liquid | Pv | psia (kPa) | True vapor pressure of the stored product at storage temperature |
| Product molecular weight | Mv | lb/lb-mol (kg/kg-mol) | Vapor molecular weight of the stored product |
| Product temperature | T | °R (K) | Average storage temperature (often approximated by liquid surface temperature) |
| Turnover factor | KN | — | Dimensionless factor related to the number of turnovers per year |
| Paint condition factor | Fp | — | Emissivity/absorptivity factor for roof (depends on paint color and condition) |
| Roof type factor | Kr | — | Factor accounting for roof shape (cone, dome, flat) |
Losses are calculated using separate expressions for standing loss (LS) and working loss (LW). The total evaporative loss is the sum of the two. The equations incorporate vapor pressure, molecular weight, temperature, tank geometry, and operational data.
Standing Storage Loss Equation
LS = Vv × KE × KS
Where KE is a vapor expansion factor depending on diurnal temperature variation and paint characteristics, and KS is a product factor based on vapor pressure and molecular weight.
Working Loss Equation
LW = 0.0010 × Mv × Pv × Q × KN × KP
Where Q is the annual net throughput, KP is a working loss product factor, and 0.0010 is an empirical constant for consistency of units.
Important: The loss calculations require careful measurement of stored liquid properties and tank operating conditions. Users must apply correction factors for breather valve settings and gas blanketing when applicable. The report recommends using site-specific data wherever possible rather than default values.
Implementation Highlights
Successful adoption of API TR 2567-2005 for emission estimates involves several practical considerations:
- Data collection: Gather tank dimensions (diameter, height, roof type), product composition, temperature profiles, and detailed throughput records.
- Vapor pressure determination: Use ASTM D6377 or API MPMS Chapter 7 (Reid vapor pressure) combined with temperature conversion equations from the report.
- Paint and roof condition: Regular inspection to determine paint solar absorptance and aging factors significantly affect standing losses.
- Software integration: Many best-practice emission inventory tools (e.g., EPA’s TANKS 4.09D) implement the API TR 2567-2005 methodology; however, users should verify that the version matches the report’s 2005 update.
Good Practice: A quality assurance plan should be developed that documents all input parameters and assumptions. Every three years, re-evaluate tank paint condition, product composition, and throughput against the original estimates to ensure accuracy remains within the expected ±30% uncertainty band stated in the report.
Compliance Notes
While API TR 2567-2005 itself is a voluntary technical guidance document, its methodology is widely referenced in regulatory frameworks:
- U.S. EPA: The report’s equations form the basis for the fixed-roof tank emission factors in AP-42 (Section 7.1). State and local air agencies often require use of AP-42, which in turn points to API TR 2567-2005 for detailed calculations.
- International use: The technical report is cited by several national environmental agencies and is often accepted as an equivalent method to local guidelines for emission estimation.
- Best available technology (BAT) assessments: When evaluating emission reduction options, the baseline calculated using API TR 2567-2005 may be compared with losses after implementing controls such as internal floating roofs or vapor recovery.
Compliance Warning: For facilities subject to Title V operating permits in the U.S., failure to use the correct version of the emission estimation methodology (e.g., using an outdated pre-2005 method when API TR 2567-2005 is referenced) can lead to permit deviations and potential enforcement actions. Always confirm with local regulators which edition is applicable.
API TR 2567-2005 includes examples with complete calculation steps to help users validate their understanding. It also provides conservative default values for tanks where detailed measurements are unavailable, but with a caution that default-based estimates are likely to overestimate actual losses by a factor of two or more.
Frequently Asked Questions about API TR 2567-2005
Q: What is the difference between API 2567 (pre-2005) and API TR 2567-2005?
A: API 2567 was originally issued as a standard in 1976. The 2005 version was reissued as a Technical Report (TR) to clarify that it provides guidance and recommended practices rather than mandatory requirements. The 2005 edition incorporates updates to vapor pressure calculation methods, introduces new paint condition factors, and aligns with API MPMS Chapter 19.2 (Evaporative Loss from Storage Tanks). The core calculation methodology remains consistent, but the technical report includes revised defaults and better uncertainty guidance.
A: API 2567 was originally issued as a standard in 1976. The 2005 version was reissued as a Technical Report (TR) to clarify that it provides guidance and recommended practices rather than mandatory requirements. The 2005 edition incorporates updates to vapor pressure calculation methods, introduces new paint condition factors, and aligns with API MPMS Chapter 19.2 (Evaporative Loss from Storage Tanks). The core calculation methodology remains consistent, but the technical report includes revised defaults and better uncertainty guidance.
Q: Can API TR 2567-2005 be applied to tanks storing non‑petroleum chemicals?
A: The methodology is most accurate for hydrocarbon liquids with vapor pressures between 0.1 and 15 psia. For other chemicals, especially those with strongly non-ideal vapor‑liquid equilibrium or those stored below ambient temperature, the assumptions in the report (e.g., constant vapor composition) may not hold. It is recommended to use industry‑specific guidance or perform a detailed mass‑balance analysis for such chemicals.
A: The methodology is most accurate for hydrocarbon liquids with vapor pressures between 0.1 and 15 psia. For other chemicals, especially those with strongly non-ideal vapor‑liquid equilibrium or those stored below ambient temperature, the assumptions in the report (e.g., constant vapor composition) may not hold. It is recommended to use industry‑specific guidance or perform a detailed mass‑balance analysis for such chemicals.
Q: How does API TR 2567-2005 account for breather valve settings?
A: The report includes a modification factor for standing losses when the tank is equipped with a breather valve (pressure/vacuum vent). The set points affect the vapor space pressure and thus the vapor expansion factor. The equations incorporate a correction that reduces standing loss when the valve prevents low pressure venting. Specific guidance is provided in Section 5.2.2 of the report.
A: The report includes a modification factor for standing losses when the tank is equipped with a breather valve (pressure/vacuum vent). The set points affect the vapor space pressure and thus the vapor expansion factor. The equations incorporate a correction that reduces standing loss when the valve prevents low pressure venting. Specific guidance is provided in Section 5.2.2 of the report.
Q: Is the API TR 2567-2005 method applicable globally?
A: While the report was developed primarily for US conditions (e.g., using US customary units), the equations are dimensionally consistent. SI unit conversions are provided in an appendix. Many international emission estimation guidelines (e.g., European Environment Agency’s EMEP/EEA air pollutant emission inventory guidebook) reference the API TR 2567 methodology as an acceptable alternative, provided that local meteorological and product data are used.
A: While the report was developed primarily for US conditions (e.g., using US customary units), the equations are dimensionally consistent. SI unit conversions are provided in an appendix. Many international emission estimation guidelines (e.g., European Environment Agency’s EMEP/EEA air pollutant emission inventory guidebook) reference the API TR 2567 methodology as an acceptable alternative, provided that local meteorological and product data are used.