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API MPMS 10.7 (2002, Reaffirmed 2011) – Displacement Measurement of Liquid Hydrocarbons Using a Discrete Integrator and Mechanical Prover
Technical guide to the scope, methodology, and compliance requirements of API Manual of Petroleum Measurement Standards Chapter 10.7 for meter proving in custody transfer.
API MPMS Chapter 10.7 (2002, Reaffirmed 2011) provides a standardized test method for determining the meter factor of liquid hydrocarbon meters using a mechanical displacement prover in conjunction with a discrete integrator. The discrete integrator counts electrical pulses generated by a meter-mounted pulse output device (e.g., a turbine meter pickup or a positive displacement meter pulser) and compares them to the known volume of the prover during a proving run. This method is essential for custody transfer applications where high accuracy is required, such as pipeline, terminal, and refinery operations.
The standard forms part of the API Manual of Petroleum Measurement Standards (MPMS), which is widely recognized as the authoritative reference for measurement practices in the hydrocarbon industry. It covers equipment requirements, test procedure, calculation of meter factor, and acceptance criteria. The following sections provide a detailed look at the scope, technical requirements, implementation considerations, and compliance aspects of this standard.
1. Scope and Application
API MPMS 10.7 applies to the proving of turbine and positive displacement meters that are equipped with a pulse output device and used to measure the volume of liquid hydrocarbons. The method requires a mechanical displacement prover (either unidirectional or bidirectional) and a discrete integrator capable of counting pulses with high resolution and zero error. The standard specifically addresses the procedure for determining the meter factor at flowing conditions and correcting it to base conditions using appropriate temperature and pressure corrections. It is intended for meters in clean, single-phase liquid service where the liquid is hydrocarbon based.
Tip: The discrete integrator must have a minimum pulse resolution of 10,000 pulses per prover volume to achieve the accuracy required by the standard. Always verify the integrator’s compatibility with the prover detector switches before testing.
The standard also outlines the required number of proving runs, the acceptable repeatability limits, and how to handle out-of-tolerance results. It is routinely referenced in fiscal metering contracts and regulatory requirements across North America and many other regions.
2. Technical Requirements and Methodology
2.1 Equipment Specifications
The proving system comprises three main components:
- Mechanical Displacement Prover: A calibrated tube that uses a sphere or piston to displace a fixed volume between two detectors. The prover volume must be traceable to national standards and calibrated to an accuracy of ±0.02% or better.
- Meter with Pulse Output: The meter (turbine or positive displacement) must produce an electrical pulse train proportional to the volume passed. The pulse output must have a sufficient frequency and clean signal to avoid missed or extra counts.
- Discrete Integrator: An electronic counter that records the number of pulses between the start and stop detector signals from the prover. The integrator must be verified for accuracy and must not introduce counting errors under operating conditions.
Temperature and pressure measurements are also critical. Temperature sensors must be accurate within ±0.5 °F and pressure sensors within ±1 psi. All instruments should be calibrated regularly and have current traceable certificates.
2.2 Proving Procedure
The proving procedure is carried out as follows:
- Establish stable flow through the meter and prover at the desired flow rate (typically within the meter’s linear range).
- Initiate the proving run by starting the discrete integrator when the prover sphere passes the first detector.
- The integrator stops counting when the sphere passes the second detector, having displaced a known volume of liquid.
- Record the pulse count, temperature, pressure, and prover volume. Correct the prover volume to base conditions using API MPMS Chapter 11.1 volume correction factors.
- Compute the meter factor: Meter Factor = (Prover Volume at Base Conditions) / (Pulse Count).
- Repeat the run a minimum of three times. More runs are required if the repeatability criteria are not met.
Warning: Fluctuations in flow rate, temperature, or pressure during a proving run can invalidate the results. Allow the system to stabilize for at least 60 seconds before initiating each run.
2.3 Repeatability and Acceptance Criteria
The standard defines maximum allowable deviations between consecutive meter factors. The following table summarizes typical repeatability limits based on prover volume:
| Prover Volume (U.S. Gallons) | Acceptable Repeatability (of mean) | Max Deviation Between Any Two Runs |
|---|---|---|
| ≤ 100 | ±0.05% | 0.02% |
| 101 – 500 | ±0.02% | 0.01% |
| > 500 | ±0.02% | 0.01% |
Table 1: Typical repeatability limits for meter proving per API MPMS 10.7 (2002, R2011)
If the repeatability exceeds these limits, the cause must be investigated (e.g., entrapped air, flow instability, instrument error) and the proving run must be repeated after corrective action.
2.4 Corrections to Base Conditions
The prover volume and the meter reading must be corrected to the same base conditions (usually 60 °F and 0 psig). The standard references API MPMS Chapter 11.1 for volume correction factors (VCF) and API MPMS Chapter 12 for calculation procedures. The meter factor is then expressed at base conditions, which is used to convert future meter pulse counts to volumes.
3. Implementation Best Practices
To obtain reliable and consistent meter factors, practitioners should adhere to the following best practices:
- Calibrate the prover at intervals not exceeding 12 months or as mandated by local regulations.
- Install meters with adequate straight-pipe runs upstream (at least 10 pipe diameters) to ensure fully developed flow.
- Use flow conditioners if necessary to stabilize flow profile.
- Monitor the discrete integrator’s background counts (pre- and post-run) to verify that no false pulses are counted.
- Maintain a log of all meter factors to detect long-term drift or meter wear.
- Train proving technicians on the correct interpretation of the standard and the equipment.
Note: A well-maintained proving system operating in accordance with API MPMS 10.7 can achieve overall measurement uncertainty of less than ±0.15%, which is suitable for custody transfer.
4. Compliance and Regulatory Notes
API MPMS 10.7 is not a legal requirement by itself, but it is often incorporated by reference into contracts, tariffs, and government regulations (e.g., in the United States under 49 CFR Part 195 for pipeline measurement). Many international petroleum companies mandate compliance with the MPMS standards for all custody transfer metering.
The 2011 reaffirmation indicates that the technical committee found the 2002 edition still current and valid. However, users should always check for the latest edition or addendum that may have been published since reaffirmation. The MPMS is updated periodically; as of 2026, Chapter 10.7 remains the 2002 edition with reaffirmation in 2011.
Important: Regulatory authorities in some jurisdictions may require the use of specific MPMS chapters or impose additional proving frequency. Always verify local requirements before designing a proving program.
The standard is applicable globally, but users outside North America should also consider that some countries have adopted ISO 7278 or national standards that may differ. In such cases, API MPMS 10.7 can still be used as a mutual agreement between parties.
Frequently Asked Questions
Q: What is the difference between API MPMS 10.7 and API MPMS 10.4?
A: API MPMS 10.7 covers the use of a mechanical displacement prover with a discrete integrator, where the prover provides the reference volume. API MPMS 10.4 describes the master meter method, where a secondary reference meter is used instead of a prover. The choice depends on available equipment, flow rate, and accuracy requirements.
A: API MPMS 10.7 covers the use of a mechanical displacement prover with a discrete integrator, where the prover provides the reference volume. API MPMS 10.4 describes the master meter method, where a secondary reference meter is used instead of a prover. The choice depends on available equipment, flow rate, and accuracy requirements.
Q: How many proving runs are required for a valid meter factor?
A: The standard requires a minimum of three consecutive runs that meet repeatability criteria. If the criteria are not met, additional runs (typically 5 to 10) are performed until the deviation is acceptable. Some operators require a minimum of five runs for added confidence.
A: The standard requires a minimum of three consecutive runs that meet repeatability criteria. If the criteria are not met, additional runs (typically 5 to 10) are performed until the deviation is acceptable. Some operators require a minimum of five runs for added confidence.
Q: Can this standard be used for non-hydrocarbon liquids such as water or chemicals?
A: Although written specifically for liquid hydrocarbons, the principles may be applied to other liquids provided that appropriate volume correction factors (VCF) are used and fluid properties are considered. However, the standard does not cover calibration fluids or chemicals; consult the governing contract or standard for such applications.
A: Although written specifically for liquid hydrocarbons, the principles may be applied to other liquids provided that appropriate volume correction factors (VCF) are used and fluid properties are considered. However, the standard does not cover calibration fluids or chemicals; consult the governing contract or standard for such applications.
Q: Is the discrete integrator the same as a flow computer?
A: No. A discrete integrator is a dedicated counter that accumulates pulses from the meter and is controlled by the prover detectors. A flow computer may also perform this function, but it can introduce additional uncertainties if not properly configured. The standard specifically refers to a discrete integrator for accuracy verification. Many modern proving systems use a flow computer that includes a dedicated proving module.
A: No. A discrete integrator is a dedicated counter that accumulates pulses from the meter and is controlled by the prover detectors. A flow computer may also perform this function, but it can introduce additional uncertainties if not properly configured. The standard specifically refers to a discrete integrator for accuracy verification. Many modern proving systems use a flow computer that includes a dedicated proving module.
Article prepared in 2026 for informational purposes. Always reference the latest official version of API MPMS 10.7 for compliance and application.