1、 AGA Report No. 7 Measurement of Natural Gas by Turbine Meters Revised February 2006 Prepared by Transmission Measurement Committee Copyright 2006 American Gas Association 400 North Capitol Street, NW, 4th Floor, Washington, DC 20001, U.S.A. Phone: (202) 824-7000 Fax: (202) 824-7082 Web: www.aga.org
2、 Catalog # XQ0601 . . iiDISCLAIMER AND COPYRIGHT The American Gas Associations (AGA) Operating Section provides a forum for industry experts to bring collective knowledge together to improve the state of the art in the areas of operating, engineering and technological aspects of producing, gathering
3、, transporting, storing, distributing, measuring and utilizing natural gas. Through its publications, of which this is one, the AGA provides for the exchange of information within the gas industry and scientific, trade and governmental organizations. Each publication is prepared or sponsored by an A
4、GA Operating Section technical committee. While AGA may administer the process, neither the AGA nor the technical committee independently tests, evaluates, or verifies the accuracy of any information or the soundness of any judgments contained therein. The AGA disclaims liability for any personal in
5、jury, property or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on AGA publications. The AGA makes no guaranty or warranty as to the accuracy and completeness of any informa
6、tion published therein. The information contained therein is provided on an “as is” basis and the AGA makes no representations or warranties including any express or implied warranty of merchantability or fitness for a particular purpose, In issuing and making this document available, the AGA is not
7、 undertaking to render professional or other services for or on behalf of any person or entity. Nor is the AGA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advi
8、ce of a competent professional in determining the exercise of reasonable care in any given circumstances. The AGA has no power, nor does it undertake, to police or enforce compliance with the contents of this document. Nor does the AGA list, certify, test, or inspect products, designs, or installati
9、ons for compliance with this document. Any certification or other statement of compliance is solely the responsibility of the certifier or maker of the statement. The AGA does not take any position with respect to the validity of any patent rights asserted in connection with any items which are ment
10、ioned in or are the subject of AGA publications, and the AGA disclaims liability for the infringement of any patent resulting from the use of or reliance on its publications. Users of these publications are expressly advised that determination of the validity of any such patent rights, and the risk
11、of infringement of such rights, is entirely their own responsibility. Users of this publication should consult applicable federal, state, and local laws and regulations. The AGA does not, through its publications intend to urge action that is not in compliance with applicable laws, and its publicati
12、ons may not be construed as doing so. This report is the cumulative result of years of experience of many individuals and organizations acquainted with the measurement of natural gas. However, changes to this report may become necessary from time to time. If changes in this report are believed appro
13、priate by any manufacturer, individual or organization, such suggested changes should be communicated to AGA by completing the last page of this report titled, “Form for Suggestion to Change AGA Report No. 7, Measurement of Natural Gas by Turbine Meters“ and sending it to: Operations all documents s
14、hall be dated: a) A description of the meter, giving technical characteristics and principle of operation. b) A perspective drawing or photograph of the meter c) A list of parts with a description of their constituent materials d) A dimensional drawing e) A drawing showing locations of seals f) A dr
15、awing of the data plate or badge, showing arrangement of inscriptions g) Instructions for installation, operation, and periodic maintenance h) A general description of operation i) A description of available mechanical outputs and electronic output signals, and any adjustment mechanisms j) A descrip
16、tion of available electronic interfaces, wiring points and essential characteristics k) Documentation of compliance with applicable safety codes and regulations l) Test report of meter performance 95. Performance Requirements 5.1 General Performance Tolerances The manufacturer shall specify flow rat
17、e limits for Qmin, Qtand Qmaxfor each meter design and size. Meter performance at atmospheric pressure shall be within the following tolerances (see also Figure 1) after calibration. Repeatability: 0.2% from Qminto Qmax, Maximum peak-to-peak error: 1.0% above Qt, Maximum error: 1.0% from Qtto Qmax,
18、and, 1.5% from Qminto Qt, Transition flow rate: Qtnot greater than 0.2 Qmax. Note 1. The tolerances apply after adjustment of the change gears (if any) and/or setting of K-factors and application of the final meter factor. Note 2. The tolerances apply after any corrections performed within the meter
19、 itself but prior to the application of any linearization algorithms by equipment auxiliary to the meter. Note 3. These tolerances are applicable at atmospheric pressure. As operating gas pressure increases, the performance of the turbine meter can be expected to improve dramatically, with smaller v
20、alues for repeatability and maximum peak-to-peak error, provided the meter is calibrated for the intended operating conditions. Qt 0.2 QmaxQminFlow rate (Qi) Maximum peak-to-peak error 1.0% (Qi Qt) Repeatability +/-0.2% Percent error-1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00
21、1.25 1.50 1.75 Figure 1. Turbine Meter Tolerances at Atmospheric Pressure 105.2 Temperature and Gas Composition Influences The turbine meter shall meet the above performance requirements over the full operating range of temperature and gas composition. 5.3 Pressure Influences Research on the effects
22、 of pressure on turbine meter performance was conducted in 2002 and 2003, and the results published in Reference 3. To minimize error, turbine meters should be calibrated for the applicable operating conditions. Guidance on calibration requirements is provided in Section 6. 5.4 Meter Body Interchang
23、eability Meters with interchangeable measurement cartridges are designed so that the measurement cartridge can be removed from the meter body without removing the body from the installation. This design facilitates in situ inspection and replacement or upgrading of a cartridge. The construction of a
24、 meter with an interchangeable measurement cartridge shall be such that the performance characteristics specified in Section 5.1 are maintained after installation of the cartridge in other meter bodies of the same manufacturer, size and model, or after repeated removal and installation of the measur
25、ement cartridge in the same meter body. However, slight differences in geometry from the body in which the cartridge was calibrated, body wear, cartridge-body misalignment or other influences may affect the performance of the cartridge and result in measurement error. An independent study (Reference
26、 4) was conducted to assess measurement error due to cartridge change-out practices. The study indicates that operating a cartridge in a body other than the one in which it was calibrated can introduce random measurement errors from a negligible amount to as much as 0.35%. Turbine meter users should
27、 bear in mind that calibration of measurement cartridges on a stand-alone basis, while convenient and less expensive than calibrating a cartridge and body as a combination, can add to measurement error. 116. Individual Meter Tests 6.1 Integrity Test The manufacturer shall test the integrity of all p
28、ressure-containing components for every turbine meter. The test shall be conducted in compliance with the appropriate industry standard, (ANSI/ASME B16.1, B16.5, B16.34 or other, as applicable). 6.2 Leakage Test Every turbine meter shall be leak-tested by the manufacturer after final assembly and pr
29、ior to shipment to the customer or flow-calibration facility. The test shall be conducted in compliance with the appropriate industry standard. In the absence of specific standard(s), it is customary for manufacturers to conduct the test as follows: The test medium shall be a gas, such as nitrogen o
30、r air. The leak-test pressure shall be at least 1.10 times the MAOP and held for a minimum of five minutes. To pass this test, the meter must not have detectable leaks. 6.3 Calibration In order to establish satisfactory performance characteristics, every turbine meter should be calibrated under cond
31、itions acceptable to and agreed upon between the parties to the transaction. For best performance, calibration conditions should match the anticipated in-service conditions, including considerations such as fluid characteristics, operating pressure, expected flow rates, the use of a dedicated meter
32、body, inlet and outlet piping characteristics, and other factors that can affect meter performance. However, limitations on the capability and availability of calibration facilities and the costs associated with transportation and testing may result in decisions to calibrate meters under conditions
33、that, while not identical to those expected in service, provide a reasonable approximation thereof. Attention to replication of the crucial in-service parameters described below will ensure adequate performance for most commercial applications. 6.3.1 Calibration Conditions Research (Reference 3) has
34、 shown that the performance of turbine meters varies with changes in flow rate and operating pressure. These variations are related to changes in Reynolds number and, in some cases density, and are particularly significant at low and intermediate operating pressures and flow rates. Attention to thes
35、e issues at the time of calibration is crucial for optimal measurement. The following sections provide further guidance in this regard. 6.3.1.1 Reynolds Number Reynolds number is a dimensionless ratio of inertial to viscous forces in the flow through the meter that takes into account the flow rate a
36、nd physical properties of a moving fluid. Reynolds number can be used to correlate the calibration and operating conditions of a turbine meter under various flow rates, pressures and fluid types. 12The basic equation for Reynolds number is: Re = (D) (V) / (6.1) Reynolds number may also be calculated
37、 from either of the following formulae: Re = 4(Q)/ (D) () (6.2) Re = 4 (Q) () / (D) () (6.3) where Re = Reynolds number (rho) = Density D = Meter diameter V = Bulk (average) velocity of flowing fluid Q = Volumetric flow rate (nu) = Kinematic viscosity (mu) = Absolute viscosity The above quantities m
38、ust all be determined at the same conditions of temperature and pressure. The relationship between bulk velocity and flow rate is: Q = V D 2/ 4 (6.4) The relationship between absolute and kinematic viscosity and density is: = / (6.5) A meter calibration carried out in a test facility over a particul
39、ar range of Reynolds numbers characterizes the meters performance when used to measure gas over the same range of Reynolds numbers when the meter is in service. Therefore, the K-factors established during such a calibration, in most instances, can be used to compute flow measured by the meter in ser
40、vice. 6.3.1.2 Density Research (Reference 3) has shown that the performance of some meters may also be sensitive to variations in gas density. Variations in calibration tend to be larger at lower gas densities. Users with low-pressure, low-flow applications should consult the meter manufacturer for
41、meter performance characteristics and obtain calibration data at the operating density to ensure that no significant measurement errors exist. Additional information on density matching is provided in Appendix E. 6.3.1.3 Calibration Gases The research described in Reference 3 was conducted using nat
42、ural gas and air as test media. In addition, Reference 6 describes research that has been conducted to establish the suitability of other gases for calibration of turbine meters. The data show that turbine meters used in natural gas can be effectively calibrated in different 13gases, and that satisf
43、actory measurement will result provided calibration is conducted over the range of Reynolds numbers and/or density expected at operating conditions. Further information on calibration in alternative gases is provided in Appendix E. 6.3.2 Calibration Guidelines As discussed above, the expected operat
44、ing Reynolds number range and/or density for a meter needs to be taken into account when designing a calibration program. This requires establishing the expected range of flow rates and the properties of the gas to be measured at the intended meter location. The gas properties may be determined dire
45、ctly by measurement or by calculation from empirical equations. Test points should be selected throughout the range of flow rates over which the meter is to be tested. It may be decided to concentrate the majority of the test points in the range of the meters heaviest expected usage. Further informa
46、tion and sample calculations appear in Appendix E. 6.3.3 Calibration Configuration To minimize errors, meters should be calibrated in the same configuration as intended to be installed in service. However, most test facilities routinely perform calibrations in the recommended configuration described
47、 in Section 7.2. Research (Reference 2) has shown that the errors of meters calibrated in this manner will be acceptable when installed in any of the configurations described in Section 7.2. For applications with more severe installation configurations, the user should consult the manufacturer or te
48、st facility operator for experimental data to determine an adequate calibration configuration. 6.3.4 Calibration Facilities Test facilities used for meter calibration shall be able to demonstrate traceability to relevant national primary standards and provide test results that are comparable to thos
49、e from other such facilities. 6.3.5 Calibration Results During calibration, the appropriate K-factor(s), meter factors, change gears ratios and rotor factors will be established. The applicable factors will be established for each output for meters with more than one output. Refer to Appendix D for detailed information and examples of determining and applying these factors. 6.3.5.1 Change Gears For turbine meters with mechanical output(s), internal gear
