Standards for electronic flow metering systems

Within the pipeline industry, measurement specialists have long recognized the important ways in which automation and information technology affect the volumetric and energy flow measurement function. When discussing these topics, the issue of relevant industry standards becomes increasingly important.

The applicable United States industry standard for the electronic equipment and systems used to acquire, process, and store natural gas pipeline flow measurement data in an electronic form is Chapter 21.1 of the American Petroleum Institute (API) Manual of Petroleum Measurement Standards (MPMS). Chapter 21.1 is entitled Flow Measurement Using Electronic Metering Systems. As stated in its scope, Chapter 21.1 describes the minimum specifications for electronic gas measurement systems used in the measurement and recording of flow parameters of gaseous phase hydrocarbons. Topics covered in the standard include definitions, calculation algorithms, data availability, audit and reporting requirements, equipment installation, calibration, and verification and security.

Chapter 21.1 of the API MPMS was originally published in August 1993, when electronic recording of measurement data began to be implemented industry-wide. Around that time, microprocessor technology began to replace the chart (i.e., pen and paper) method of recording flow measurement parameters, such as differential pressure across the plate of an orifice flow meter. Between 1993 and now, the development of electronic metering systems has proceeded at a rapid pace. However, Chapter 21.1 has remained unchanged that entire time.  Now, however, the API is about to release a new, updated version of this standard.  The revised Chapter 21.1 has been balloted by the API membership and is undergoing final revision before release.  Watch for the posting soon of the revised document on the API website (www.api.org).

Newly revised chapter

The revised Chapter 21.1 will address the technology advancements that have occurred since the original version was published. The original document primarily focused on the use of electronic metering systems for orifice and turbine flow meters. The new version, which is over twice the length of the original, will address orifice, turbine, ultrasonic, Coriolis, rotary, and diaphragm flow meters, among others.

Compliance test protocols

One of the shortcomings of the original version of Chapter 21.1 was the lack of testing protocols for assessing whether or not electronic metering systems provided accurate output data and complied with the requirements specified in the document. This has resulted varying interpretation of compliance and lack of consistency in assessing compliance by those who manufacture electronic metering systems. The new version of Chapter 21.1 will include protocols designed to test the accuracy of flow computer averaging, integral value, and flow time calculation algorithms. Also included in the new document will be a checklist to be used during the on-site commissioning of new electronic metering systems. This will help operators ensure that new equipment installations operate correctly and reliably from the outset.

Future needs

In the future, we will see changes that are even more significant in the way measurement data are electronically acquired, stored, transmitted, processed, and utilized. In the not-too-distant future, the “standard” flow meter configuration could be an integrated package including the flow element, all secondary measurement instrumentation (e.g., pressure, temperature, gas composition, etc.); onboard computing power sufficient to not only perform the required engineering calculations, but also diagnose the operational health of the package (and self-correct any identified problems); and communication gear capable of transmitting the data elsewhere. Today’s conventional flow meter installation – a flow element, externally-mounted secondary instrumentation, and a “flow computer” used to acquire, store, process, and transmit the measurement data – may no longer be the norm. Another revision of API MPMS Chapter 21.1 will be required at that time to stay current with the technology of the day. n