Updates to API 21.1

ByBrian Sowell

October 16, 2019

Did you know that API 21.1 underwent some massive updates in 2013? Here’s a rundown of the latest version.

Natural gas measurement operations must comply with API MPMS Chapter 21, Section 1 (also known as “API 21.1”), Flow Measurement Using Electronic Metering Systems—Electronic Gas Measurement. Updated in 2013, the second edition includes substantial revisions to the original version.

API 21.1 is further described, here. It is essentially a minimum requirements specification for gas measurement systems and focuses primarily on digital flow computers.

While a digital flow computer is typically installed at the meter site, API 21.1 2nd edition has added descriptions of “off-site” calculations that could be performed, instead, by a PC or other computer system.

Although digital flow computers provided the driving force for API 21.1, the standard encompasses the entire gas measurement system. This includes a centralized measurement application such as FLOWCAL by Quorum Software, plus all the communications avenues for transfer of measurement information from meters, analyzers, chromatographs, and testing laboratories to the measurement application.

API 21.1 broadly defines three stages of measurement: primary, secondary, and tertiary.

The primary stage is the physical meter such as a Coriolis meter, orifice meter, turbine meter, or ultrasonic meter.

The secondary stage includes sensors, transducers, or transmitters that measure live variables such as differential pressure across an orifice plate, static pressure in the meter tube, temperature of the gas in the meter tube, and pulse count or frequency from primary devices such as turbine meters.

The tertiary stage includes one or more devices or systems that perform flow computations. API 21.1 2nd edition further describes measurement computer systems that make corrections to input data and re-run flow calculations.

API MPMS Chapter 21.1 contents include the following:

  • Scope – gas measurement system overview
  • Normative References – references to publications such as AGA reports and API MPMS standards
  • Descriptions, Definitions, and Symbols – descriptions of system components with an update particularly including data management, plus an extensive glossary and symbols list, which were not in the original version
  • Electronic Gas Measurement Algorithms – describes algorithms for differential and linear meters
  • Audit and Record Requirements – the data log is notably called the “quantity transaction record” (QTR) and a newly-described, corrected QTR is included; alarm, event and configuration logs are also described
  • Data Availability – describes onsite and off-site data requirements
  • Commissioning – describes documentation requirements and commissioning of primary, secondary, and tertiary devices
  • Equipment Verification and Calibration – defines maintenance practices and the verification/calibration process for primary devices and other gas measurement equipment
  • Security and Data Integrity – description of data integrity is new; defines access protection and algorithm protection

Among all-new appendices are:

  1. Rans Methodology for Estimating Sampling Frequency and Calculation Algorithm Errors
  2. Averaging Techniques
  3. Correction Methodology
  4. Calculation of Normal Operating Range and Percent Fluctuation
  5. Example Flow Computer Variable Input Type Testing – Differential Meters
  6. Example Commissioning Checklist
  7. Examples of Configuration Log Data
  8. Calculation of Differential Pressure “As-Found”
  9. Example of a Redundancy Verification Report
  10. Examples of Applying Linear Meter Equations
  11. Example of Using DPIV and DPY and a Volumetric Flow Rate Calculator to Recalculate a QCP or QTR

Note that those measurement departments, which are tracking both natural gas and liquid hydrocarbons, must comply with API 21.2 as well as API 21.1. API MPMS Chapter 21, Section 2, Electronic Liquid Volume Measurement Using Positive Displacement and Turbine Meters, was released in 1998. An addendum, Flow Measurement Using Electronic Metering Systems, Inferred Mass, followed in 2000.

If you want to see how FLOWCAL by Quorum Software can help you manage API measurement requirements, schedule a demo with our measurement experts.

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