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API MPMS 19.2 (2003): Evaporative Loss Measurement from Storage Tanks — Incorporating API Publ 2517 & 2519
A comprehensive technical guide to the calculation methods, data requirements, and compliance framework for assessing evaporative losses in petroleum storage
Scope of API MPMS 19.2 (2003)
API MPMS 19.2 (2003) — also known as API Publ 2517 and API Publ 2519 — is the definitive industry standard for estimating evaporative losses from atmospheric petroleum storage tanks. It forms Chapter 19.2 of the API Manual of Petroleum Measurement Standards (MPMS). The standard addresses both fixed-roof tanks (vertical and horizontal) and external floating-roof tanks, providing calculation methodologies to quantify two primary loss mechanisms:
- Standing storage losses – vapor emissions caused by daily temperature and pressure fluctuations (breathing losses).
- Working losses – emissions displaced during filling and emptying operations.
The scope includes tanks storing volatile organic liquids (VOCs) such as gasoline, crude oil, and condensate, with vapor pressures below the normal boiling point. Tanks operating at ambient pressure (atmospheric and low-pressure) are covered; refrigerated or pressurized tanks are excluded.
Tip: API MPMS 19.2 is widely recognized by environmental agencies (e.g., U.S. EPA) as a reference method for emission inventory reporting and regulatory compliance under 40 CFR Part 60 and 63.
Technical Requirements
Emission Estimation Equations
The core of API MPMS 19.2 is a set of empirical equations that relate emissions to tank characteristics, product properties, and meteorological conditions. Two distinct calculation approaches are provided:
- Tank-Specific Method – requires detailed tank dimensions, paint condition, and site-specific meteorological data (wind speed, solar insolation, vapor pressure, etc.).
- Average Tank Method – uses default factors for a “typical” tank, suitable for screening-level estimates or when detailed data are unavailable.
Key input variables include:
- Tank geometry (diameter, height, roof type, seal configuration)
- Product vapor pressure (true vapor pressure at storage temperature)
- Product molecular weight and liquid composition
- Annual throughput and average turnover frequency
- Paint solar absorptance and thermal conductance
- Ambient temperature, wind speed, and daily solar insolation
Important: Vapor pressure must be adjusted for actual storage temperature, not standard conditions. API MPMS 19.2 provides correlations for estimating true vapor pressure from Reid vapor pressure (RVP).
Table 1 — Typical Loss Components by Tank Type
| Tank Type | Loss Component | Primary Factors | Example Equation Ref. |
|---|---|---|---|
| Fixed Roof (vertical) | Standing storage loss | Vapor space volume, temperature range, vapor pressure | Eq. 2.2-1 (breathing) |
| Fixed Roof (vertical) | Working loss | Throughput, vapor pressure, saturation factor | Eq. 2.2-2 |
| External Floating Roof | Standing storage loss | Seal type, wind speed, deck fit, rim gaps | Eq. 3.2-1 |
| External Floating Roof | Working loss | Withdrawal rate, product clingage, vapor pressure | Eq. 3.2-2 |
| Fixed Roof (horizontal) | Standing + working loss | Diameter, length, fill frequency, vapor pressure | Eq. 2.3-1 & 2.3-2 |
Each equation includes empirically derived emission factors (e.g., for seal losses, welding loss, column loss) that reflect typical industry experience.
Implementation Highlights
Data Collection and Quality
Successful application of API MPMS 19.2 requires accurate input data. The standard recommends:
- Using actual tank dimensions from calibration or construction drawings.
- Obtaining product vapor pressure from laboratory analysis (ASTM D6377 or D2879).
- Retrieving meteorological data from a nearby weather station representative of the tank site.
- Assessing paint condition (absorptance categories range from 0.17 for white paint to 0.97 for black/weathered surfaces).
Many operators use dedicated emission estimation software (e.g., the EPA TANKS program) that implements the API MPMS 19.2 algorithms. The 2003 edition explicitly aligned the calculation procedures with the EPA model, ensuring consistent application.
Best Practice: For emission inventories, always document the calculation method (tank-specific vs. average tank), input sources, and any default factors used to allow regulatory review and future reproducibility.
Common Pitfalls
- Incorrect vapor pressure: Using RVP instead of true vapor pressure at storage temperature can underestimate losses by over 50%.
- Neglecting fittings and seal gaps: Floating-roof tank losses are dominated by rim seal and deck fitting emissions; using outdated seal factors may lead to non-compliance.
- Ignoring meteorological variability: Using annual averages for solar insolation and wind speed can mask seasonal extremes that drive breathing losses.
Compliance Notes
API MPMS 19.2 is not a regulatory standard itself, but it is widely mandated or recommended by international authorities for emission reporting and regulatory compliance:
- United States (EPA): 40 CFR Part 60 Subparts Kb, Va, and 40 CFR Part 63 Subpart CC directly reference API MPMS 19 for tank emission calculations. The EPA’s TANKS program uses the same algorithms.
- Europe: The European Pollutant Release and Transfer Register (E-PRTR) and many Member States accept API MPMS 19.2 as the best available methodology for estimating storage losses from mineral oil refineries.
- Canada: Environment Canada’s “Environmental Code of Practice for Aboveground Storage Tanks” cites API MPMS 19.2 as the reference method for volatile organic compound (VOC) emission calculations.
Caution: Regulatory jurisdictions may impose specific conditions on the use of API MPMS 19.2, such as requiring the tank-specific method for all significant emission units, or mandating the use of default factors only when actual data are unavailable. Always verify local requirements.
The standard’s 2003 edition superseded the earlier API Publications 2517 (1989) and 2519 (1995). Operators who still rely on the older documents should update their emission estimation procedures to align with the latest version, which reflects improved empirical data and expanded coverage for new seal technologies.
Frequently Asked Questions
Q: What is the primary difference between API Publ 2517/2519 and API MPMS 19.2 (2003)?
A: API MPMS 19.2 integrated and harmonized the previous separate publications for fixed-roof tanks (2517) and floating-roof tanks (2519) into a single chapter of the MPMS. The 2003 edition added updated emission factors for modern seal designs, clarified the handling of vertical fixed-roof tanks with dome roofs, and aligned calculation procedures with the U.S. EPA’s TANKS model.
A: API MPMS 19.2 integrated and harmonized the previous separate publications for fixed-roof tanks (2517) and floating-roof tanks (2519) into a single chapter of the MPMS. The 2003 edition added updated emission factors for modern seal designs, clarified the handling of vertical fixed-roof tanks with dome roofs, and aligned calculation procedures with the U.S. EPA’s TANKS model.
Q: Can API MPMS 19.2 be applied to tanks storing non-petroleum liquids (e.g., organic chemicals)?
A: The method is developed for hydrocarbon mixtures typical of petroleum and condensate. For pure chemicals or highly non-ideal mixtures, the vapor pressure and molecular weight inputs may still be accurate, but the empirical emission factors (e.g., for seal losses) are based on petroleum service. External validation or alternative methods (such as EPA’s AP-42 or TANKS with custom factors) may be necessary.
A: The method is developed for hydrocarbon mixtures typical of petroleum and condensate. For pure chemicals or highly non-ideal mixtures, the vapor pressure and molecular weight inputs may still be accurate, but the empirical emission factors (e.g., for seal losses) are based on petroleum service. External validation or alternative methods (such as EPA’s AP-42 or TANKS with custom factors) may be necessary.
Q: How often should a tank emission calculation be updated under API MPMS 19.2?
A: The standard itself is a calculation method, not a periodic requirement. However, for regulatory inventories, an annual update is common, or whenever tank geometry, product service, throughput, or paint condition changes significantly. The EPA’s Greenhouse Gas Reporting Program (40 CFR Part 98) requires recalculation when new data become available.
A: The standard itself is a calculation method, not a periodic requirement. However, for regulatory inventories, an annual update is common, or whenever tank geometry, product service, throughput, or paint condition changes significantly. The EPA’s Greenhouse Gas Reporting Program (40 CFR Part 98) requires recalculation when new data become available.
Q: Does API MPMS 19.2 cover internal floating-roof tanks?
A: The standard explicitly covers external floating-roof tanks. For internal floating-roof tanks (tanks with fixed roofs and internal floats), the calculation methods are analogous but the standard recommends using the fixed-roof equations with modifications for the internal deck and seal system. Detailed guidance for internal floating roofs was added in the 2003 edition.
A: The standard explicitly covers external floating-roof tanks. For internal floating-roof tanks (tanks with fixed roofs and internal floats), the calculation methods are analogous but the standard recommends using the fixed-roof equations with modifications for the internal deck and seal system. Detailed guidance for internal floating roofs was added in the 2003 edition.
This article was prepared for informational purposes in 2026. Always consult the latest edition of API MPMS 19.2 and applicable local regulations for official compliance requirements.