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TagsGases Density Fluid Dynamics Natural Gas Accuracy And Precision
File Size4.3 MB
Total Pages85
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Page 84

It is the intention to publish the results of this work in a report as an
alternate to the present table. This work will be coordinated with AGA-3
revision since super-compressibility gets into the definition of base conditions
and of specific gravity as presently used in AGA-3.

AGA-3 has become an American National Standards Institute standard ANSI/API 2530
with its publication in 1978. The basic document is the same, but it has been
reprinted with the introductory paragraph change to reflect that it is now a
standard and not just a committee report as it was in the past. This gives the
report additional legal standing.

In passing, it may be of interest to those of you that are familiar with another
publication of the AGA Transmission Measurement Committee, The Gas Measurement
Manual, that this is progressing and shortly Chapters 1 through 11A will be
available. The original intention was to put this out as a complete reference,
but because of the problems of getting all of the chapters ready at once the
decision was made to publish each chapter as a separate entity. These can be
added to a loose leaf binder so that eventually you could purchase all chapters
and have a complete book. This also eases the job of updating the work. For
those of you who are not familiar with this manual, it is a detailed write-up of
all aspects of gas measurement (i.e., primary elements, secondary elements,
station design, auxiliary equipment, testing procedures, etc.) that are not
covered in the basic standard and yet are required to obtain proper measurement.
The new book is being written by a combined committee of the Transmission and
Distribution Measurement Committees of the AGA and will cover both areas of
measurement—transmission and distribution.

There is one special application of an orifice meter that may be of interest in
that it represents a blending of the technology of the liquid and gas
measurement people. Tests are being run on orifice and turbine meters tested in
place with a mechanical displacement prover. The particular purpose is to try to
improve the accuracy of a meter system to a few tenths of a percent in a
critical measurement application on ethylene, which is roughly five times as
expensive as natural gas. The philosophy is that there is enough money involved
so that an in-place throughput test against a known standard (the volume of the
prover) is justifiable. The meter, then, would have a factor applied as
indicated by the test. The significance of the test is that it breaks away from
the philosophy that, if mechanical requirements are met, then the orifice meter
is accurate. It gets into factoring a meter to a standard that has been used for
years by the liquid measurement people. The facility is by no means inexpensive,
but it will be interesting to watch the results since it would afford an
in-place throughput test that could define errors that might not be known
otherwise. It bears watching, and within the next year or so there should be
test results published in industry publications and papers presented at meter
schools on the subject. Whether it affects AGA-3 or not, it may affect testing
procedures for gas meters.


In summary, there is continued work being done to further improve the ability to
get accurate measurement in the following areas: basic test work, data handling,
manufacturing and special applications. The overall goal is to develop an
orifice meter installation that will provide for measurement within a precision
limit of plus or minus 0.2%. suitable for computer application. The milestones
or objectives that must be achieved in attainment of this goal include:

1. Re-derivation of the basic coefficient (present work).

Page 85

2. Redefining super-compressibility, including both basic structures add general
3. Redefinition of expansion factor.
4. Interference studies to determine tube configuration and the impact of both
interference and correcting devices.
5. Mathematical interpretation.
6. Industry acceptance and revision of AGA-3.
This work is in various degrees of completion and will be affecting the manner
in which the standards are revised and the way we apply orifice meters. We
should stay aware of the work as it is completed to be able to plan on its
implementation to our use of orifice meters.

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