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Introduction to API MPMS Chapter 22.2
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Introduction to API MPMS Chapter 22.2
API Manual of Petroleum Measurement Standards (MPMS) Chapter 22.2, originally published in 2005 and reaffirmed in 2012, establishes a rigorous testing protocol for differential pressure (DP) flow measurement devices used in petroleum and natural gas applications. This standard is essential for achieving traceable, repeatable, and accurate flow measurements in custody transfer, allocation, and process control. By defining minimum requirements for test facilities, reference standards, data acquisition, and uncertainty analysis, API MPMS 22.2 provides a unified framework that aligns with international standards such as ISO 5167 and ASME MFC-14M.
The standard applies to common DP devices including orifice plates (concentric, eccentric, and segmental), venturi meters, nozzles, and cone meters. It is designed to be used by manufacturers, testing laboratories, end users, and regulatory bodies to ensure consistent performance evaluation across the industry.
Scope and Applicability
API MPMS 22.2 covers the complete lifecycle of DP device testing – from laboratory calibration to field verification. The scope includes:
- Establishment of test facility requirements (flow loops, pressure/temperature instrumentation, fluid properties measurement)
- Specification of reference flow meters and primary standards (gravimetric, volumetric, or master meter traceable to national standards)
- Definition of test procedures, data collection protocols, and rejection criteria
- Guidance on uncertainty analysis in accordance with the ISO Guide to the Expression of Uncertainty in Measurement (GUM)
- Documentation and reporting formats for test results
Tip: API MPMS 22.2 does not replace device-specific standards like ISO 5167 but complements them by providing the overarching testing framework. Always use the current edition of ISO 5167 for dimensional tolerances and discharge coefficient equations.
The standard explicitly covers tests performed with liquid water or dry gases (including air and natural gas) at ambient to moderate conditions. High-pressure or high-temperature testing (e.g., supercritical fluids) is considered an extension and requires additional documentation.
Technical Requirements and Testing Protocol
Test Facility Specifications
The standard imposes strict requirements on the calibration facility to minimize systematic errors. Key requirements include:
- Stable flow conditions achieved through straight upstream piping (lengths as per API MPMS Chapter 14.3 / AGA Report No. 3) and flow conditioners where necessary
- Temperature sensors with ±0.1°C accuracy, pressure transmitters with ±0.05% full-scale accuracy
- Density measurement via inline densitometers or derived from pressure, temperature, and composition (with proper EOS)
Reference Measurement System
A reference flow measurement system with an expanded uncertainty (k=2) of ≤0.10% for liquid and ≤0.20% for gas tests is mandated. This typically requires traceable gravimetric or high-accuracy master meters.
| Parameter | Liquid Test Requirements | Gas Test Requirements |
|---|---|---|
| Reference uncertainty (k=2) | ≤ 0.10 % | ≤ 0.20 % |
| Minimum number of test points | ≥ 21 (over flow range) | ≥ 21 (over flow range) |
| Repeatability per test point | ≤ 0.10 % | ≤ 0.20 % |
| Flow range covered | 10 % to 100 % of max | 10 % to 100 % of max |
| Fluid temperature stability | ± 0.5 °C | ± 1.0 °C |
Data Collection and Uncertainty Analysis
Data must be collected at steady-state conditions with adequate sampling time (minimum 60 seconds for most applications). The standard mandates a full uncertainty budget according to the GUM methodology, including contributions from:
- Reference standard uncertainties (Type A and Type B)
- Device dimensional measurements (bore diameter, beta ratio, edge sharpness, etc.)
- Pressure and temperature measurement
- Fluid property models (density, viscosity, isentropic exponent)
- Data acquisition system resolution
- Repeatability and reproducibility
Important: The standard requires that the combined expanded uncertainty of the device under test shall be stated in the test report. Report all uncertainties at a 95% confidence level (k=2). Failure to provide a full uncertainty budget is a common non-conformance during audits.
Implementation Highlights and Best Practices
Implementing API MPMS 22.2 in a testing program involves several practical considerations:
Facility Qualification
Before formal testing, the facility must undergo a qualification process to verify that all measurement systems meet the required uncertainties. Inter-laboratory comparisons or round-robin tests with accredited partners are strongly recommended.
Device Preparation
All DP devices must be examined for mechanical condition and dimensional compliance with the relevant device standard (e.g., API MPMS Chapter 14.3 for orifice plates). Any damage, wear, or out-of-tolerance dimensions must be documented and may disqualify the test.
Success Factor: Laboratories that implement a robust quality management system (e.g., ISO 17025) alongside API MPMS 22.2 find that audit results improve dramatically. The standard’s testing protocol naturally aligns with accreditation requirements for measurement traceability.
Data Handling and Reporting
The standard provides specific templates for reporting test results, including tabulated discharge coefficients (Cd), Reynolds numbers, and deviation plots. It is considered best practice to include both raw data and corrected values in the final report.
Non-compliance Risk: Incorrect application of the temperature correction for the thermal expansion of the meter body (the ‘thermal expansion coefficient’ of the meter material) is one of the most frequent sources of error in DP meter testing. Ensure that all corrections follow the equations given in Appendix B of the standard.
Additional implementation tips include:
- Use continuous scanning or averaging over the test period rather than single-point readings to reduce random error
- Conduct “as-left” verification after any maintenance or dimensional changes
- Maintain a documented change control process for test loops and instrumentation
Compliance Notes and Industry Relevance
API MPMS 22.2 serves as the fundamental testing protocol for DP flow meters used in custody transfer applications where fiscal metering accuracy is critical. Compliance is often stipulated in contractual agreements between pipeline operators, refineries, and storage terminals. Key compliance considerations:
- Testing must be performed by a laboratory that has been assessed against the requirements of API MPMS 22.2, either by the API itself or by an accredited third party.
- The standard does not mandate recalibration intervals; these are typically defined by regulations, company policy, or API MPMS Chapter 21 (Flow Measurement Using Electronic Metering Systems).
- For orifice meters used in natural gas measurement, the calibration data obtained under API MPMS 22.2 can be used to derive site-specific discharge coefficients, improving accuracy over the generic equation of ISO 5167.
- The 2012 reaffirmation confirmed the original 2005 text, but users should check for any addenda or inline corrections published on the API website.
Adoption of API MPMS 22.2 is also encouraged for non-custody applications (e.g., allocation meters) as it provides a standardized method for quality assurance and uncertainty traceability. The protocol is fully compatible with the broader API MPMS framework, especially Chapters 14.3 (Orifice Metering) and 5 (Metering Assemblies).
Q: Which DP flow measurement devices are covered by API MPMS 22.2?
A: The standard covers all common differential pressure devices, including concentric, eccentric, and segmental orifice plates, venturi meters (classical and truncated), flow nozzles (ISA 1932, ASME long-radius), and cone-type meters. It does not apply to pitot tubes, averaging probes, or variable-area meters.
A: The standard covers all common differential pressure devices, including concentric, eccentric, and segmental orifice plates, venturi meters (classical and truncated), flow nozzles (ISA 1932, ASME long-radius), and cone-type meters. It does not apply to pitot tubes, averaging probes, or variable-area meters.
Q: How does API MPMS 22.2 relate to ISO 5167?
A: ISO 5167 provides the geometry tolerances and discharge coefficient equations for specific DP devices. API MPMS 22.2 complements this by defining the testing protocol — how to calibrate and verify those devices in a controlled laboratory setting. They are meant to be used together.
A: ISO 5167 provides the geometry tolerances and discharge coefficient equations for specific DP devices. API MPMS 22.2 complements this by defining the testing protocol — how to calibrate and verify those devices in a controlled laboratory setting. They are meant to be used together.
Q: What are the minimum requirements for a test facility to be considered compliant with this standard?
A: The facility must have a reference measurement system with expanded uncertainty ≤0.10% (liquid) or ≤0.20% (gas), stable flow conditions, temperature/pressure instrumentation with defined accuracy, and the ability to calculate a full GUM uncertainty budget. Additionally, the facility should have a quality system in place that documents procedures and personnel competence.
A: The facility must have a reference measurement system with expanded uncertainty ≤0.10% (liquid) or ≤0.20% (gas), stable flow conditions, temperature/pressure instrumentation with defined accuracy, and the ability to calculate a full GUM uncertainty budget. Additionally, the facility should have a quality system in place that documents procedures and personnel competence.
Q: Is API MPMS 22.2 recognized by regulatory bodies for custody transfer?
A: Yes. Many jurisdictions either directly require or accept testing per API MPMS 22.2 for fiscal metering applications. It is also referenced in API Ch. 14.3 and is widely adopted by the American Petroleum Institute’s calibration services for flow meters. For cross-border pipelines, adherence to this standard helps satisfy international contractual requirements.
A: Yes. Many jurisdictions either directly require or accept testing per API MPMS 22.2 for fiscal metering applications. It is also referenced in API Ch. 14.3 and is widely adopted by the American Petroleum Institute’s calibration services for flow meters. For cross-border pipelines, adherence to this standard helps satisfy international contractual requirements.
© 2026 — This technical article is for informational purposes only and does not constitute official interpretation of the API MPMS 22.2 standard. Users should refer to the latest published edition of the standard for definitive requirements.
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