1、 AGA Report No. 9 Measurement of Gas by Multipath Ultrasonic Meters Second Edition April 2007 2006 A i G A i ti All i ht dAGA Report No. 9 Measurement of Gas by Multipath Ultrasonic Meters Second Edition April 2007 Transmission Measurement Committee Copyright 2007, Operating Section, American Gas As
2、sociation 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 Catalog # XQ0701 iDISCLAIMERS AND COPYRIGHT The American Gas Associations (AGA) Operating Section provides a forum for industry experts to bring collective knowl
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14、 Operations i.e., they are bi-directional. The designer should specify if bi-directional measurement is required so that the manufacturer can properly configure the SPU parameters. The designer/operator is cautioned that operating ultrasonic meters at low gas velocities, less than 2 ft/sec, may incu
15、r greater measurement uncertainty due to thermal gradients across the pipe. 73.5 Upstream Piping and Flow Profiles Upstream piping configurations (i.e., various combinations of upstream fittings, valves, regulators, and lengths of straight pipe) may affect the gas velocity profile entering a UM to s
16、uch an extent that significant flow rate measurement error results. The magnitude and sign of the error, if any, will be, in part, a function of the ability of the meter to correctly compensate for such conditions. In general, research results have shown that this effect is dependent on the meter de
17、sign, as well as the type and severity of the flow field distortion produced at the meter. Although a substantial amount of data is available on the effect of upstream piping, the full range of field piping installation configurations has not been studied in detail. Meter station designers/operators
18、 may gain insight into expected meter performance for given upstream piping installation configurations by soliciting available test results from meter manufacturers or by reviewing test data found in the open literature. However, to truly confirm meter performance characteristics for a particular p
19、iping installation configuration, flow calibration of the metering package is usually required. In order to achieve the desired meter accuracy, it may be necessary for a designer/operator to alter the original piping configuration or include a flow conditioner as part of the meter installation. Furt
20、her recommendations are provided in Sections 7.2.2 and 7.2.7 of this report. 3.6 Acoustic Noise The presence of acoustic noise in a frequency range coincident with a UMs operating frequency, may interfere with pulse detection and, therefore, transit time measurement. If the UM cannot detect pulses,
21、their transit times between transducers cant be measured and flow measurement ceases. Acoustic noise interference can also cause pulse “mis-detection” resulting in erroneous transit time measurements that translate into volumetric errors. Users must consider whether interfering acoustic noise is ant
22、icipated at a particular installation and take steps to prevent adverse effects on UM performance during the station design phase. Acoustic noise may be generated from numerous sources related to gas flow turbulence: high gas velocities through piping and/or fittings, protruding probes, flow conditi
23、oners, or pressure and regulating control valves, etc. Since UM manufacturers specify the operating frequencies of their transducers, the frequency range in which a particular meter might be affected by acoustic noise is known. Dynamic operating conditions (flow, pressure and temperature) and the va
24、riety of acoustic noise generators make prediction of offending noise frequencies difficult. Consequently, decoupling a UMs operating frequency from piping system noise can be challenging. Manufacturers recognize the potential for operating problems, and most UMs have diagnostic outputs that indicat
25、e when acoustic noise impairs meter performance. Strategies, as follows, have also been devised by users and manufacturers to estimate and/or limit a UMs susceptibility to noise interference. Enhanced signal processing to improve ultrasonic pulse recognition and detection Signal filtering to narrow
26、the bandwidth surveyed for better/faster pulse recognition Installation of fittings, such as blind tees or filters, to isolate noise source from the UM Development and deployment of specialized silencers that are installed in the piping between UM and noise sources to isolate the meter from the offe
27、nding noise Evaluation of UM response to acoustic noise prior to station installation Additional attenuation between noise source and UM, if required, could include blind tees or other fittings or acoustic filters. (The user should be aware that close-coupling of pipe fittings, such as blind Tee fit
28、tings, may distort velocity profiles.) 8In general, noise sources upstream of UMs have a more adverse impact on meter performance than those installed downstream, although downstream installation of pressure reduction or other noise generating equipment doesnt guarantee interference wont occur. Also
29、, greater separation between a noise source and the UM equipped with an increased number of fittings, provides more attenuation than if meter and source are installed in close proximity to one another. When considering installation of a UM, particularly in the vicinity of pressure or flow regulators
30、, the following factors should be assessed during the station design phase. The valves (i.e., noise source) installed position relative to the meter upstream or downstream, distance between meter and source, number and type of fittings between meter and source. Operating frequency of the meters ultr
31、asonic transducers and the range of frequencies generated by the noise source (noise reduction trim valves are of particular concern since the design generates noise exceeding audible frequencies, which are often times in the ultrasonic range). Whether additional attenuation between noise source and
32、 UM is required, which could include blind tees or other fittings or acoustic filters. Whether enhanced filtering of digital signal processing should be applied, and if so, whether it slows signal processing time beyond acceptable limits (limits prescribed for a linear measuring device are in API MP
33、MS Chapter 21.1). When installation of a UM near a potential noise source is anticipated, it is recommended users contact manufacturers for recommendations specific to their products prior to finalizing station design. Cooperation between users and manufacturers during facilities design can avoid th
34、e need for potentially expensive remedial actions at a completed meter installation. 94. Meter Requirements 4.1 Codes and Regulations The meter body and all other parts, including the pressure-containing structures and external electronic components, shall be designed and constructed of materials su
35、itable for the service conditions for which the meter is rated and in accordance with any codes and regulations applicable to each specific meter installation, as specified by the designer. Unless otherwise specified by the designer, the meter shall be suitable for operation in a facility subject to
36、 the U.S. Department of Transportations (DOT) regulations in 49 C.F.R. Part 192, Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards. 4.2 Quality Assurance The manufacturer shall establish and follow a written comprehensive quality-assurance program for the producti
37、on, assembly and testing of the meter and its electronic system (e.g., ISO 9000, API Specification Q1, etc.). This quality-assurance program should be available to the inspector. 4.3 Meter Body 4.3.1 Maximum Operating Pressure Meters should be manufactured to meet one of the common pipeline flange c
38、lasses ANSI Class 150, 300, 600, 900, etc. The maximum design operating pressure of the meter should be the lowest of the maximum design operating pressure of the following: meter body, flanges, transducer connections, transducer assemblies. The required maximum operating pressure shall be determine
39、d using the applicable codes for the jurisdiction in which the meter will be operated and for the specified environmental temperature range. The designer should provide the manufacturer with information on all applicable codes for the installation site and any other requirements specific to the oper
40、ator. 4.3.2 Corrosion Resistance All wetted parts of the meter shall be manufactured of materials compatible with natural gas and related fluids. All external parts of the meter should be made of a non-corrosive material or sealed with a corrosion-resistant coating suitable for use in atmospheres ty
41、pically found in the natural gas industry and/or as specified by the designer. 4.3.3 Meter Body Lengths and Bores The manufacturer shall publish standard its overall face-to-face length of the meter body with flanges, for each ANSI flange class and diameter. For meters without flanges, the manufactu
42、rer shall publish its standard overall length of the measurement section for each diameter size and schedule. The meter inside diameter in the measurement section shall be of constant diameter to within 0.5% of the average internal diameter of the measurement section. The measurement section average
43、 internal diameter shall be determined by a minimum of four equally-spaced individual internal diameter measurements made in a plane at the meter measurement section entry, middle, and exit. 10For a meter having a bore diameter different from the associated metering package piping a transition taper
44、 is allowed as long as it conforms to the meter performance requirements outlined in this document. The designer shall specify requirements, such as pinning or companion flanges, for ensuring alignment of the meter and the associated metering package piping. Alignment is necessary to ensure that met
45、er performance in-situ is not degraded from that during calibration because of changes in the alignment of upstream and downstream components, such as conditioners and probes. 4.3.4 Ultrasonic Transducer Ports Because natural gas may contain some impurities (e.g., light oils, glycols, amines, inhibi
46、tors or condensates), transducer ports should be designed in a way that reduces the possibility of liquids or solids accumulating in the transducer ports. If specified by the designer and available from the manufacturer, the meter should be equipped with valves and necessary additional devices, moun
47、ted on the transducer ports in order to make it possible to replace the ultrasonic transducers without depressurizing the meter run. In that case, a bleed valve may be required in addition to the isolation valve to ensure that no pressure exists behind a transducer before releasing the extraction me
48、chanism. 4.3.5 Pressure Tap At least one pressure tap shall be provided for measuring the static pressure in the meter body. This pressure tap is designated for use in determining corrected volume. Each pressure-tap hole should be between 1/8“ and 3/8“ nominal inside diameter and cylindrical over a
49、length at least 2.5 times the diameter of the tapping, measured from the inner wall of the meter body. The tap hole edges at the internal wall of the meter body should be free of burrs and wire edges, and have square edges. For a meter body with a wall thickness less than 5/16“, the hole should be 1/8“ nominal in diameter. Female pipe threads should be provided at each pressure tap for a 1/4“ NPT or 1/2“ NPT isolation valve. Turning radius clearance should be provided to allow a valve body to be screwed directly into the pressure tap. Pressure taps ca
