Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
API MPMS Chapter 19.3E (1997, reaffirmed 2002): Evaporative Loss from Storage Tanks – Correlation Method
A Comprehensive Guide to Scope, Technical Requirements, and Compliance for Estimating Storage Tank Evaporative Losses
Scope and Application
API MPMS Chapter 19.3E (1997, reaffirmed 2002) – often referenced as API MPMS 19.3E 1997 (2002) – specifies a correlation method for estimating evaporative losses from atmospheric storage tanks containing petroleum liquids. The standard applies to both fixed roof and floating roof (external and internal) tank designs and covers losses during standing storage (breathing) as well as working losses during filling and emptying operations. This chapter is part of the Manual of Petroleum Measurement Standards (MPMS) and is widely adopted by environmental agencies, including the U.S. Environmental Protection Agency, for emission inventory reporting and regulatory compliance.
Technical Requirements and Methodology
Fundamental Loss Equations
The correlation method separates evaporative loss into two components: standing storage loss (due to normal thermal and barometric changes) and working loss (due to liquid level changes). Each component is derived from basic vapor–liquid equilibrium principles and tank geometry. The standard provides detailed equations that incorporate key variables such as vapor pressure, liquid temperature, tank diameter, wind speed, and product volatility.
Key Input Parameters
Accurate estimation depends on reliable data for:
- Product true vapor pressure at the average liquid surface temperature
- Tank dimensions (diameter, height, roof type)
- Meteorological conditions (ambient temperature, wind speed, solar insolation)
- Paint condition and color (affects tank surface temperature)
- Seal and fitting configurations for floating roof tanks
Default Emission Factors and Correlations
Chapter 19.3E provides tables of default emission factors for various tank components (rim seals, deck fittings, deck seams) when site-specific measurements are unavailable. These factors are based on empirical data collected under typical operating conditions. The following table summarizes the main loss components and key variables for common tank types:
| Tank Type | Loss Component | Key Variables | Equation Reference |
|---|---|---|---|
| Fixed Roof (including fixed cone, dome, or umbrella) | Standing storage loss (breathing) | Vapor pressure, temperature, tank size, paint color | Eq. 3E-1 |
| External Floating Roof | Rim seal loss | Seal type, wind speed, liquid properties, tank diameter | Eq. 3E-5 |
| External Floating Roof | Deck fitting loss | Fitting type, number of fittings, wind speed | Eq. 3E-6 |
| Internal Floating Roof (with fixed roof) | Rim seal and deck loss | Seal type, deck construction, vapor pressure | Eq. 3E-8 |
| All Types | Working loss (fill/empty) | Throughput, vapor pressure, tank geometry | Eq. 3E-2 |
Calculation Procedures
The standard prescribes a step-by-step procedure for calculating annual evaporative losses. For fixed roof tanks, the standing storage loss is a function of the vapor space volume, vapor pressure, and a combination of temperature and atmospheric pressure variations. Floating roof losses are estimated by summing the contributions from the rim seal, deck fittings, and any deck seams, with corrections for product properties and wind conditions. Working losses are computed from the total annual throughput and the average vapor pressure of the loaded product.
Tip: When using the default emission factors provided in the standard, verify that the tank configuration matches the factor’s underlying assumptions. For critical applications (e.g., regulatory permit limits), consider performing site-specific measurements or using the more rigorous direct measurement methods described in other chapters of MPMS Chapter 19.
Warning: The correlation method may overestimate losses for tanks located in very low wind regions or storing high vapor pressure products. In such cases, the use of alternative estimation methods or adjustments may be necessary to avoid excessively conservative emission reports.
Implementation Highlights
Practical application of the standard requires careful assembly of input data and validation of assumptions. Key implementation steps include:
- Data Collection: Obtain accurate tank geometry from construction drawings, confirm product vapor pressure from representative laboratory analysis, and acquire local meteorological data (annual averages or monthly patterns).
- Configuration Identification: Classify the tank according to roof type, seal type, and fitting inventory. The standard provides detailed identification charts and photographs for typical tank components.
- Application of Correction Factors: Apply factors for paint color, condition, and insulation. The standard includes a table of correction factors for solar absorptivity and tank skin temperature.
- Documentation: Maintain a traceable record of all input values, calculation steps, and assumptions. This is essential for regulatory audits and future updates.
Software and Tools
Many operators implement the correlation method through dedicated emission estimation software (e.g., EPA’s TANKS program, which historically incorporated the API 19.3E correlations). The standard recommends verifying that any third-party tool correctly implements the equations and default values as printed in the 1997 reaffirmed text.
Success: A robust data management system that automatically captures tank status, product data, and meteorological records can streamline the estimation process and significantly reduce human error. Organizations that integrate these data flows often see improved audit readiness and faster turnaround for regulatory reports.
Critical: The 2002 reaffirmation did not update the technical content of the 1997 edition. However, later revisions of API MPMS Chapter 19.3E (e.g., 2014 edition, 2022 edition) have introduced new emission factors and methodology improvements. Always confirm with your regulatory authority which edition is acceptable for compliance reporting. Using an outdated edition may lead to inaccurate estimates or non-compliance.
Compliance and Quality Assurance
Regulatory bodies generally accept the API MPMS 19.3E correlation method as a conservative and defensible approach for estimating evaporative losses from storage tanks. To ensure compliance:
- Conduct Sensitivity Analysis: Evaluate how variations in key parameters (especially vapor pressure and wind speed) affect the calculated emissions. This helps identify which inputs require the most accurate measurement.
- Periodic Validation: Compare calculated losses against measured product vapor recovery or inventory reconciliation data when available. Systematic deviations may indicate incorrect input values or the need to update tank configuration records.
- Training: Personnel responsible for emission estimates should be trained on the specific equations and default factors in the standard. Misapplication of seal or fitting factors is a common source of error.
- Third-Party Review: For large facilities or permits with strict emission limits, consider engaging an independent auditor to review the estimation methodology and input data for consistency with the standard.
The standard itself recommends that calculations be performed using consistent units (SI or USC as defined in the chapter) and that all intermediate values be retained for verification.
Frequently Asked Questions
Q: How does API MPMS Chapter 19.3E differ from other parts of Chapter 19?
A: Chapter 19.3E provides a correlation method that uses empirical equations and default factors. Other subsections (e.g., 19.3A for fixed roof tanks, 19.3B for external floating roof tanks, 19.3D for marine vessel loading) can offer more specific procedures or direct measurement protocols for those tank types. However, 19.3E is often used as a unified method covering all atmospheric storage tank configurations when detailed data are limited.
A: Chapter 19.3E provides a correlation method that uses empirical equations and default factors. Other subsections (e.g., 19.3A for fixed roof tanks, 19.3B for external floating roof tanks, 19.3D for marine vessel loading) can offer more specific procedures or direct measurement protocols for those tank types. However, 19.3E is often used as a unified method covering all atmospheric storage tank configurations when detailed data are limited.
Q: Can this correlation method be applied to refrigerated or pressurized storage tanks?
A: No. The correlation method is explicitly intended for atmospheric storage tanks (operating at or near ambient pressure). Refrigerated liquefied gas storage and pressurized spheres require different estimation approaches, such as those described in API MPMS Chapter 19.2 or specialized guidelines for cryogenic tanks.
A: No. The correlation method is explicitly intended for atmospheric storage tanks (operating at or near ambient pressure). Refrigerated liquefied gas storage and pressurized spheres require different estimation approaches, such as those described in API MPMS Chapter 19.2 or specialized guidelines for cryogenic tanks.
Q: How often should input parameters like vapor pressure or tank paint condition be reassessed?
A: The standard does not prescribe a specific update frequency, but best practice is to review parameters whenever there is a change in product service, tank maintenance (e.g., repainting, seal replacement), or at least annually for regulatory reporting. For volatile products, vapor pressure should be verified against current laboratory analysis.
A: The standard does not prescribe a specific update frequency, but best practice is to review parameters whenever there is a change in product service, tank maintenance (e.g., repainting, seal replacement), or at least annually for regulatory reporting. For volatile products, vapor pressure should be verified against current laboratory analysis.
Q: Is the 1997 (reaffirmed 2002) version still accepted by international regulators?
A: Acceptance varies. Many environmental agencies (e.g., US EPA) accept the 1997 edition as a valid methodology, but some may require compliance with the latest edition. It is essential to check with the applicable authority (e.g., EU ETS, local air quality boards) before selecting the edition. The correlation method itself remains scientifically sound, but newer editions include updated emission factors that may affect the results.
A: Acceptance varies. Many environmental agencies (e.g., US EPA) accept the 1997 edition as a valid methodology, but some may require compliance with the latest edition. It is essential to check with the applicable authority (e.g., EU ETS, local air quality boards) before selecting the edition. The correlation method itself remains scientifically sound, but newer editions include updated emission factors that may affect the results.
© 2026 Technical Standards Review. This article provides general guidance; always consult the official API publication for complete requirements.