API MPMS 9.3-2024
Standard Test Method for Density, Relative Density, and API Gravity of Crude Petroleum and Liquid Petroleum Products by Thermohydrometer Method
- Standard No.
- API MPMS 9.3-2024
- Release Date
- 2024
- Published By
- American Petroleum Institute (API)
- Latest
- API MPMS 9.3-2024
- Introduction
Standard Overview and Technical Background
ASTM D6822-23 is the latest version of Chapter 9.3 of the Manual of Petroleum Measurement Standards (MPMS). It specifies the method for determining the density, relative density, and API gravity of crude oil, petroleum products, and mixtures of petroleum and non-petroleum products using a thermometer. This standard, with its fourth edition released in January 2024, reflects the latest developments in petroleum measurement technology.
The thermometer method evolved from the traditional hydrometer method. By integrating a thermometer and hydrometer into a single instrument, the efficiency and accuracy of field measurements are significantly improved. This integrated design is particularly suitable for use in pipeline transportation, oilfield sites, and other locations with limited laboratory facilities.
Measurement Principle and Technical Requirements
This standard, based on the Archimedean principle, determines density by observing the position of a thermometer in a liquid. There are several correction factors to consider during the measurement process:
Correction type Applicable conditions Correction method Degree of influence Meniscus correction Opaque liquid Measured or standard value (0.5kg/m³) Moderate Correction for thermal glass expansion All measurements Calculation formula correction Significant (when temperature difference is large) Alternative calibration temperature correction Non-standard calibration temperature Temperature difference calculation Depending on temperature difference Reference Temperature Correction All measurements Petroleum meters Required Density calculation formulas are based on international standard tables, obtained by correcting readings at the observed temperature to a standard temperature of 15°C or 60°F. Key calculation formulas include:
API gravity calculation formula: °API = (141.5/relative density) - 131.5
Thermal glass expansion correction factor: HYC = 1.0 - [0.000023(t-15)] - [0.00000002(t-15)²]
Instrument and Equipment Requirements
The standard has strict regulations on the specifications of thermal hydrometers, which are mainly divided into two categories: density hydrometers and API hydrometers:
Instrument Type Measuring Range Graduation Temperature Range Standard No. Density Hydrometer 600-1100kg/m³ 0.5kg/m³ -20~+105°C 300H-309H API Hydrometer -1~+101°API 0.1°API 0~220°F 41H-60H Instrument Verification Requirements: All thermohydrometers must be verified or certified every 24 months, and thermometers every 6 months. Verification can be performed by comparison with a certified instrument or using certified reference materials (CRMs).
Detailed Operational Procedure
The standard specifies a detailed test procedure, the main steps of which include:
Sample Preparation Phase: Different mixing and temperature control strategies are adopted depending on the sample type (volatile, waxy, residual fuel oil). Volatile samples should be mixed in the original closed container, and waxy crude oils need to be heated to 9°C above the pour point or 3°C above the cloud point.
Test Temperature Selection: The optimal test temperature should be as close as possible to the reference temperature (15°C or 60°F), or within ±3°C of the bulk oil temperature. Table 3 specifies the restrictions for different sample types:
Sample type Initial boiling point Other restrictions Test temperature Volatile samples ≤120°C - ≤18°C Volatile viscous samples ≤120°C Viscosity is too high at 18°C Minimum flow temperature Non-volatile samples >120°C - -18~90°C Measurement Procedure: Transfer the sample into the hydrometer cylinder, avoiding air bubbles and loss of light components. After inserting the thermohydrometer, wait 3-5 minutes for it to stabilize before taking a reading. For transparent liquids, read directly at the bottom of the meniscus. For opaque liquids, read at the highest point of the liquid level and apply a meniscus correction.
Calculations and Data Processing
Measurement data processing requires a strict calculation process:
1. Apply the thermometer correction value and record the average temperature to the nearest 0.1°C
2. Record the observed hydrometer reading, either directly for transparent liquids or using a meniscus correction for opaque liquids
3. Apply the correction value from the hydrometer calibration certificate
4. Correct for thermal glass expansion according to the version of the petroleum meter used (1980 or 2004)
5. Correct the reading to the reference temperature using the petroleum meter
Detailed calculation examples are provided to guide the user in correctly performing unit conversions and temperature corrections. The final result should be reported as density at 15°C (accurate to 0.5 kg/m³), relative density at 60/60°F (accurate to 0.0005), or API gravity (accurate to 0.1°API).
Precision Requirements and Quality Control
Precision indicators specified in the standard:
Repeatability: The difference between two measurement results of the same sample performed by the same operator using the same equipment, under normal operating conditions, will exceed 0.6 kg/m³ or 0.2° API only once in 20 times.
Reproducibility: The difference between independent measurement results of the same sample performed by different operators in different laboratories, under normal operating conditions, will exceed 1.5 kg/m³ or 0.5° API only once in 20 times.
It should be noted that these precision figures are based on historical data and are not obtained through interlaboratory comparisons in accordance with ASTM D6300. Users are required to evaluate whether the method meets the precision requirements for their specific application.
Implementation Recommendations and Best Practices
Instrument Selection Recommendations: Select the appropriate thermopycnometer type and range based on your measurement needs. For field applications, a thermopycnometer with an integrated thermometer is recommended for increased efficiency. For laboratory applications, a separate instrument can be selected for higher accuracy.
Sample Handling Considerations: Volatile samples must be handled in a sealed container to avoid loss of light components. Waxy samples require appropriate heating to ensure thorough mixing, but the temperature should not be too high to compromise sample integrity.
Measurement Environment Control: The ambient temperature should not fluctuate by more than 3°C (5°F) during testing to prevent air flow from affecting measurement results. When using a thermostatic bath to control temperature, ensure the temperature stabilizes before taking readings.
Quality Control Measures: Establish a regular instrument verification program and maintain complete calibration records. Each measurement should be repeated to confirm the consistency of the results. The difference between the two corrected density values should not exceed 0.5 kg/m³ or 0.1° API.
Personnel training requirements: Operators should receive professional training and master the meniscus reading techniques, temperature correction methods, and calculation procedures. Especially for the measurement of opaque liquids, special training is required to accurately determine the meniscus correction value.
By strictly implementing the standard requirements and adopting these implementation recommendations, the accuracy and reliability of petroleum density measurement results can be ensured, providing reliable data support for custody transfer measurement, transportation storage, and regulatory compliance.
API MPMS 9.3-2024 history
- 2024 API MPMS 9.3-2024 Standard Test Method for Density, Relative Density, and API Gravity of Crude Petroleum and Liquid Petroleum Products by Thermohydrometer Method
- 2012 API MPMS 9.3-2012 Manual of Petroleum Measurement Standards Chapter 9.3 Standard Test Method for Density@ Relative Density@ and API Gravity of Crude Petroleum and Liquid Petroleum Products by Thermohydrometer Method (Third Edition)
- 2002 API MPMS 9.3-2002 Manual of Petroleum Measurement Standards Chapter 9—Density Determination Section 3—Standard Test Method for Density@ Relative Density@ and API Gravity of Crude Petroleum and Liquid Petroleum Products by Thermohydrometer Method (Second Edition)
- 1994 API MPMS 9.3-1994 Manual of Petroleum Measurement Standards Chapter 9 - Density Determination Section 3 - Thermohydrometer Test Method for Density and API Gravity of Crude Petroleum and Liquid Petroleum Products
