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API TR 2568-2007: Technical Report on Measurement of Liquid Hydrocarbons by Coriolis Meters
Comprehensive guidance for design, installation, operation, and compliance of Coriolis flowmeters in hydrocarbon custody transfer
Scope and Applicability
API TR 2568-2007, titled Measurement of Liquid Hydrocarbons by Coriolis Meters, provides a comprehensive technical framework for the evaluation, selection, installation, and operation of Coriolis mass flowmeters in the petroleum industry. The report is part of the API Manual of Petroleum Measurement Standards (MPMS) and serves as a complement to the more prescriptive standard API MPMS Chapter 5.6. It addresses practical aspects that are often outside the scope of the standard specification, including fluid property effects, installation sensitivities, and uncertainty analysis.
The technical report applies to the measurement of liquid hydrocarbons such as crude oil, refined products (gasoline, diesel, jet fuel), and liquefied petroleum gases (LPG) in custody transfer and allocation applications. It covers meter sizes from 1 inch (DN25) to 12 inches (DN300) and flow ranges typically from 0.1 m/s to 15 m/s. It explicitly excludes gas measurement applications and non-hydrocarbon fluids.
Tip: API TR 2568-2007 should be used in conjunction with API MPMS Chapter 5.6 and any relevant national or local metrological regulations. It is intended to reduce discrepancies between meter manufacturers and end users by providing a common reference for performance evaluation.
Technical Requirements
2.1 Meter Selection and Performance Criteria
The report specifies key performance parameters for Coriolis meters used in liquid hydrocarbon service, including base accuracy, zero stability, turndown ratio, and repeatability. Special emphasis is placed on the influence of fluid density and viscosity on the meter’s performance envelope. Table 1 summarizes typical performance specifications for meters meeting the requirements of API TR 2568.
| Parameter | Specification | Remarks |
|---|---|---|
| Base accuracy (mass flow) | ±0.10% of rate | Over 10:1 turndown at reference conditions |
| Zero stability | ±0.005% of maximum flow rate | May degrate at low flows if not properly zeroed |
| Repeatability | ±0.05% of rate | Under steady flow and temperature conditions |
| Turndown ratio | ≥20:1 | Can be extended beyond 50:1 for some designs |
| Density accuracy | ±0.5 kg/m³ | When equipped with integrated densitometer |
| Temperature effect on zero | ≤ 0.0002% of max flow per °C | Requires compensation in electronics |
| Pressure effect on meter factor | ≤ 0.005% per bar (for liquid streams) | Important for high-viscosity fluids |
2.2 Installation Requirements
API TR 2568 details installation criteria to minimize measurement error. Coriolis meters are sensitive to installation stresses, vibration, and improper support. Key requirements include:
- Pipework alignment: The meter must be installed with concentric pipework to avoid mechanical stress on the flow tubes.
- Straight pipe runs: Although Coriolis meters are largely insensitive to flow profile disturbances, a minimum of 5 pipe diameters upstream and 2 pipe diameters downstream is recommended to avoid severe swirl or two-phase flow.
- Vibration isolation: The meter should be mounted on stable supports that do not transmit pipeline or equipment vibration.
- Wiring and grounding: Signal cables must be shielded and grounded according to manufacturer’s instructions to prevent electromagnetic interference.
Warning: Failure to properly support the meter or eliminate vibration can lead to zero drift and significant measurement errors in custody transfer applications. Post-installation zero verification is mandatory.
2.3 Fluid Property Considerations
The report provides guidance on how changes in fluid density, viscosity, and composition affect the meter’s accuracy and zero stability. For instance, high-viscosity fluids may reduce the effective turndown and increase pressure drop. The report suggests using empirical correction factors or manufacturer-supplied correlations to adjust the meter factor when fluid properties deviate significantly from calibration conditions.
Implementation Highlights
3.1 Prover Loop Design and Calibration
API TR 2568 recommends that Coriolis meters be calibrated using a conventional prover loop (bidirectional or small volume) whenever possible. The report provides guidance on prover-to-meter valving, temperature equilibrium, and flow conditioning to ensure a valid traceable calibration. For meters with internal densitometers, a separate density calibration using a pycnometer or reference densitometer is advised.
3.2 Zeroing and Verification
Correct zeroing is critical for Coriolis meter performance. The report outlines a procedure for zeroing under no-flow conditions, with the meter isolated from the pipeline and filled with the fluid at operating temperature and pressure. It also describes periodic verification using a separate check meter or a small-volume prover. Table 2 shows recommended verification frequencies based on service criticality.
| Application | Verification Frequency | Method |
|---|---|---|
| Custody transfer (crude oil) | Every 6 months | Prover or master meter |
| Allocation measurement | Annually | Prover or master meter |
| Refined product transfer | Every 12 months | Small-volume prover |
| LPG measurement | Every 6 months | Master meter with pressure control |
Good practice: Keep a digital log of all zeroes and verification results. Trend analysis of zero offset and meter factor can reveal incipient issues such as tube erosion or coating build-up.
3.3 Density Measurement Integration
When Coriolis meters are used with integrated density measurement, the report provides criteria for verifying the density accuracy. It recommends that the density reading be stable within ±0.3 kg/m³ at constant conditions. Temperature compensation algorithms must be validated by comparing against laboratory analysis of fluid samples.
Compliance Notes
4.1 Legal and Regulatory Compliance
API TR 2568-2007 itself is not a mandatory standard, but it is often referenced by regulatory bodies for custody transfer applications. Compliance with its recommendations can help demonstrate due diligence in metering practices. Important regulatory frameworks that may require alignment include OIML R117 (for dynamic measurement systems) and EU Measuring Instruments Directive (MID) for relevant applications. The report encourages users to consult legal metrology authorities for any additional requirements.
Caution: Implementing Coriolis meters without adhering to the technical recommendations of API TR 2568 may result in non-acceptance by regulatory authorities, leading to fines, retroactive adjustment of measured quantities, or invalidation of custody transfer contracts.
4.2 Quality Management and Audit
The report outlines a quality assurance framework consistent with ISO 10012 and API Q1/Q2. It includes requirements for meter traceability, calibration intervals, uncertainty budget, and documentation. Regular audits should cover installation compliance, zero history, maintenance log, and training records of operators.
4.3 Documentation and Record Keeping
API TR 2568 emphasizes the importance of keeping detailed records of meter configuration, calibration certificates, software versions, and any deviation from manufacturer recommendations. The report suggests maintaining a meter file that includes:
- Manufacturer’s data sheet and commissioning report
- Calibration certificates (initial and subsequent)
- Record of zero checks and adjustments
- Fluid property changes and corrections applied
- Maintenance and repair history
The minimum retention period recommended is the service life of the meter plus five years, to support potential retroactive auditing.
Frequently Asked Questions
Q: What is the difference between API TR 2568-2007 and API MPMS Chapter 5.6?
A: API MPMS Chapter 5.6 is the normative standard that defines the minimum requirements for Coriolis meters used in hydrocarbon measurement. API TR 2568-2007 is a supporting technical report that provides additional guidance on installation, fluid effects, verification, and uncertainty analysis, without imposing mandatory requirements. Both documents should be used together for a complete understanding.
A: API MPMS Chapter 5.6 is the normative standard that defines the minimum requirements for Coriolis meters used in hydrocarbon measurement. API TR 2568-2007 is a supporting technical report that provides additional guidance on installation, fluid effects, verification, and uncertainty analysis, without imposing mandatory requirements. Both documents should be used together for a complete understanding.
Q: Can Coriolis meters be used for mass measurement of LPG with high accuracy?
A: Yes. When properly sized and installed, Coriolis meters can achieve mass flow accuracy better than ±0.25% for LPG service. However, care must be taken to maintain single-phase flow (avoid flashing or cavitation) and to apply appropriate pressure and temperature corrections for density measurement if the meter is used to derive volumetric quantities. API TR 2568 specifically addresses LPG challenges.
A: Yes. When properly sized and installed, Coriolis meters can achieve mass flow accuracy better than ±0.25% for LPG service. However, care must be taken to maintain single-phase flow (avoid flashing or cavitation) and to apply appropriate pressure and temperature corrections for density measurement if the meter is used to derive volumetric quantities. API TR 2568 specifically addresses LPG challenges.
Q: Is a flow prover required for initial calibration of a Coriolis meter under API TR 2568?
A: The report strongly recommends calibration against a primary prover or a master meter that is traceable to national standards. For custody transfer meters, a calibration every two years is considered the minimum best practice, with verification checks in between. The report also accepts calibration by the manufacturer using a recognized facility, provided a suitable certificate is provided.
A: The report strongly recommends calibration against a primary prover or a master meter that is traceable to national standards. For custody transfer meters, a calibration every two years is considered the minimum best practice, with verification checks in between. The report also accepts calibration by the manufacturer using a recognized facility, provided a suitable certificate is provided.
Q: How often should the density reading from a Coriolis meter be validated?
A: API TR 2568 suggests that the integrated density function be validated at least annually against a laboratory-certified fluid sample, or whenever the fluid composition changes significantly. Validation should confirm stability and accuracy within the specified limits for custody transfer applications.
A: API TR 2568 suggests that the integrated density function be validated at least annually against a laboratory-certified fluid sample, or whenever the fluid composition changes significantly. Validation should confirm stability and accuracy within the specified limits for custody transfer applications.
Article published in 2026. This content is provided for informational purposes and does not substitute the original standard document. For official implementation, always refer to the latest version of API TR 2568 and applicable local regulations.