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इंटरनेट मानक Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. “जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ” Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru “The Right to Information, The Right to Live” “Step Out From the Old to the New” IS 15674 (2006): Flow measurement of natural gas by ultrasonic meter [PGD 26: Weights and Measures] “!ान $ एक न’ भारत का +नम-ण” Satyanarayan Gangaram Pitroda ““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee”” “!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै” Bhartṛhari—Nītiśatakam “Knowledge is such a treasure which cannot be stolen” IS 15674:2006 I Indian Standard FLOW MEASUREMENT OF NATURAL GAS BY ULTRASONIC METER I ICS 75.160.30;75.180.30 I CJBIS2006 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 June 2006 Price Group 7 I -. Weights and Measures Sectional Committee, PG 26 FOREWORD This Indian Standard wasadopted bythe Bureau ofIndian Standards, afterthedrafl finalized bythe Weights and Measures Sectional Committee hadbeen approved bytheProduction andGeneral Engineering Division Council. This standard istaken for measuring the gasconsumption atthebulk suppliers aswell asatthe users’ end, when the gas is supplied through the pipelines. In order to meet the requirement of bulk supplier and large consumer, Bureau of Indian Standards has formulated standard for accuracy of metering system and regulation of gas at different delivery point to fulfil the consumer satisfaction as well as financial help of the organization. This standard isbasically aperformance-based specification ofIvMtipathUltrasonic Meters andshouldmeet‘orexceed the accuracy, functional and testing requirements. The users should follow the applicable installation recommendations as indicated inthis standard. In preparing this standard considerable of assistance has been taken tlom the following publications: ISO/CD 17089 Measurement of fluid flow inclosed conduits — Ultrasonic meters for gas ISO/TR 12765: 1997(E) Measurement of fluid flow in closed conduits — Methods using transit time ultrasonic flow-meters AGA 8American gas authority report for compressibility and super compressibility I AGA 9 American gas authority report for ultrasonic meters AGA 10 American gas authority report for speed of sound in natural gas and other related hydrocarbon gases OIML R6 General provisions of gas volume meters OIML D11General requirements for electronic measuring instruments I IS 15674:2006 Indian Standard FLOW MEASUREMENT OF NATURAL GAS BY ULTRASONIC METER 1 SCOPE metering facilities and purchases multipath ultrasonic meters. This standard covers multipath ultrasonic transit-time flow-meters, used for custody transfer measurement of 3.3 Inspector — Representative of the designer who natural gas for gas temperature between –10°to 55°C. visitsthemanufacturer’s facilities forquality assurance Multipath ultrasonic meters shall have at least two purposes. independent pairs of measuring transducers (acoustic 3.4 Manufacturer — Company that designs, paths). manufactures, sells and delivers multipath ultrasonic 2 PRINCIPLE OF MEASUREMENT meters. Company that operates multipath ultrasonic meters and performs normal maintenance. Multipath ultrasonic meters are inferential meters that derive the gas flowrate by measuring the transit times 3.5 ‘Flowrate — Volume per unit oftime atmetering of high-frequency sound pulses. Transit times are conditions. measured forsoundpulsestraveling diagonally across 3.6 Indication —Theflowrate indicated bythemeter. the pipe, downstream with the gas flow and upstream againstthegasflow.Thedifference inthesetransittimes 3.7 Working ‘Range — Range of flowrates of gas is related to the average gas flow velocity along the limitedbythemaximumflowrateq~~,and$e minimum acoustic paths. Numerical calculation techniques are flowrate qMin,for which the meter error lies within thenusedtocompute theaverageaxialgasflowvelocity specified limits, sometimes also called rangeability. andthe gasvolume flowrate atlineconditions through 3.8 Metering Pressure —Absolute gaspressu~ ina the meter. meter at flowing conditions to which the indicated The accuracy of an ultrasonic gas meter depends on volume of gasisrelated. several factors, such as, 3.9 Average Velocity — Flowrate per unit of cross- a) precise geometry of the meter body and sectional area. ultrasonic transducer locations; b) integration technique inherent in the design 3.10 Meter Body –-Pressure-containing structure of ofthe meter; the meter. c) quality ofthe flow profile, levels ofpulsation 3.11 Acoustic Path — Path travelled .byan acoustic that exist in the flowing gas stream and gas wave between a.pair ofultrasonic transducers. uniformity; and 3.12 Deviation — The difference between the actual d) accuracy ofthe transit-time measurements. volumeflowrate(forexample, flowrates inengineering Theaccuracy ofthetransit:time measurements depends units)measured bythe meter under test and the actual onthe electronic clock stability, volume flowrate measured by a reference meter. a) consistent detection of sound pulse wave Corrections shallbemadeforthedifferences inflowing gaspressure, temperature andcompressibility between reference positions; and the two meters. The deviation is also measured as a b) proper compensation for signal delays of differencebetweenthemassflowratethrough themeter electronic components and transducers. under test andthemassflowrate through the reference 3 TERMINOLOGY meter. T~ically, three or more test runs are averaged to establish the deviation at each nominal flowrate. For the purpose of this standard, the following These test runs can be used t.o determine the definitions shall apply: repeatability asdefined below. 3.1 Auditor —Representative oftheoperator orother 3.13 Error — The observed deviation of a meter interested party that audits operation of multipath calculated as:Percent error shallbe divided by [(Test ultrasonic meter. meter reading — Reference meter reading)/Reference 3.2 Designer — Company thatdesigns andconstru cts meter reading] x 100. 1 1S15674:2006 3.14 Maximum Error—The allowable error iimit mixture, (c) the total sulphur level exceeds 320 ppm within the specified operational range ofthe meter. approximately including mercaptans hydrogen sulphide and elemental sulphur compounds. 3.15 Maximum Peak-to-Peak Error — The largest . allowable difference between the upper-most error Deposits due to normal gas pipeline conditions (for point and the lower-most error point. example, condensates or traces ofoilmixed with mill- seal, dirt or sand) may affect the meter’s accuracy by 3.16 q~,X— The maximum gas flowrate through the reducing the meter’s cross-sectional area. Deposits USM that can he measured within the error limits. shall also attenuate or obstruct the ultrasonic sound 3.17 qt— The transition gasflowmte belowwhichthe waves emitted from and received by the ultrasonic expanded error limit is applicable, and where transducers, and in some designs reflected by the q,~ :0.1 qM,,. internal wall ofthe meter. 3.18 qMin— The minimum gas flowrate through the 4.2 Pressures USM that can be measured within the expanded error Ultrasonic transducers used in USM require a limits. minimumgasdensity(atlmction ofpressure) toensure 3.19 qi — The actual measured gas flowrate passing acoustic coupling ofthe sound pulses to and from-the through aUSM under aspecific set oftest conditions. gas.Therefore, thedesigner shallspeci~ the expected minimum operating pressure aswel1asthe maximum 3.20 Reference Meter — A meter or measurement # operating pressure. device of proven flow measurement accuracy. 3.21 Repeatability — The closeness of agreement 4.3 Temperatures, Gas and Ambient among a number of consecutive measurements of The USM should operate over a flowing gas the output of the test meter for the same reference temperature range of–10° to 55”C.Themanufacturer flowrate under the same operating conditions, shall specify the expected operating gas temperature approaching from the same direction, for full scale range. traverses. The repeatability shallcorrespond tothe 95 percent confidence interval ofthe deviation based on The operating ambient air temperature range shall the assumption of anormal distribution. be –10° to 55”C. This ambient temperature range applies to the meter body with and without gas flow, 3.22 Resolution — The smallest step by which the field-mounted electronics, ultrasonic transducers, change of the flow velocity is indicated by the meter. cabling, etc. 3.23 SPU — Signal processing unit. The manufacturer shall state the flowing gas and 3.24 USM — Ultrasonic meter. ambientairtemperature specifications forthemultipath ultrasonic meter, ifthey differ fromthe above. 3.25 Velocity Sampling Interval —Thetimeinterval between two succeeding gas velocity measurements 4.4 Metering Conditions by the full set of transducers or acoustic paths. Conditions, prevailing at the point of measurement, Typically, between 0.05 and0.5 s,depending onmeter for example, gas, composition, temperature and size. pressure. 3.26 Zero-Flow Reading —Themaximum allowable NOTE—Notpreferredalternativea:ctualconditions. flow-velocity reading when the gas is at rest; that is, both the axial and the non-axial velocity components 4.5 Baseconditions towhichthe measured volume of are essentially zero. thegasisconverte~ forexample,basetemperatureand base pressure. 4 OPERATING CONDITIONS NOTE—Notpreferredalternatives:reference-,standard-, 4.1 Gas Quality normalconditionse,tc. 4.1.1 The meter shall, as a minimum requirement, 4.6 Gas Flow Considerations operate with any of the normal range natural gas The flowrate limitsIhat may be measured by a USM composition mixtures. This includes relative densities are determined by the actual velocity of the flowing of pure methane between 0.55 and 0.87. gas. The designer should determine the expected gas The manufacturer shall be consulted if any of the flowrates and veri~ that these values are within the following are expected: (a) acoustic wave attenuation qMi”!9~and q~,Xspecified by the manufacturer. The carbon dioxide levels are above 10 percent, accuracy requirement for operation within qM,n,qtand (b) operation nearthecritical density ofthenatural gas qMax. The designer should examine carefully the 2 IS 15674:2006 maximum velocityfornoiseandpipingsafety(erosion, overall face-to-face length of the meter body with thermowave vibrations, etc) concerns. flanges, foreachANSI flange classand diameter. The designer, asan option, may specify a different length USM have the inherent capability of measuring flow to match existing piping requirements. in either direction with equal accuracy; that is, they are hi-directional. The designer should specifi if bi- The USM bore and the adjacent upstream pipe along directional measurement is required so that the with flanges should have the same insidediameter to manufacturer may properly configure the SPU within 1 percent of each other. For hi-directional parameters. applications, bothendsofthemetershallbeconsidered upstream. 4.7 Upstream Piping and Flow-Profiles 5.1.4 Ultrasonic Transducer Ports Upstream piping configurations may adversely affect the gas velocity profile entering a USM to such an As natural gas may contain some impurities (for extent that measurement error occurs. The magnitude example, light oils or condensates), transducer ports ofthe error, ifany, should beaiimction ofthemeter’s shallbe designed inawaythat reduces the possibility ability to correctly compensate for such conditions. of liquids or solids accumulating in the transducer ports. 5 METER REQUIREMENTS If specified by the designer and available from the 5.0 The meter body and all other parts, including the manufacturer, themeter shallbeequipped with valves pressure-containing structures and external electronic and necessary additional devices, mounted on the components, shall be designed and constructed of transducer ports inorder tomake itpossible toreplace materials suitable forthe service conditions forwhich the ultrasonic transducers without repressurizing the the meter is rated, and in accordance with any codes meter run. Inthat case, ableed valve maybe required and regulations applicable to each specific meter in addition to the isolation valve to ensure that no installation, asspecified bythe designer. pressure exists behind a transducer before releasing the extraction mechanism. 5.1 Meter Body 5.1.1 Maximum Operating Pressure 5.1.5 Pressure Tap Meters shall be manufactured to meet one of the At least one pressure tap shall be provided for common pipeline flange classes — ANSI Class 300, measuring the static pressure in the meter. Each 600,900, etc.Themaximum designoperating pressure pressure tap hole shall be between 3mm and 10mm ofthemetershallbethe lowestofthemaximum design nominal in diameter and cylindrical over a length at operating pressure of the following: meter body, least 2.5 times the diameter of the tapping measured flanges,transducer connections, transducer assemblies. from theinner wall of the meter body. The tap hole edges at the internal wall of themeter body shall be The required maximum operating pressure shall be free of burrs and wire edges, and have minimum determined using the applicable codes for the rounding. jurisdiction in which the meter will be operated and for the specified environmental temperature range. For.ameterbodywithawallthickness lessthan 8mm, The designer should provide the manufacturer with the hole shall be 3mm nominal indiameter. information onallapplicable codes fortheinstallation Femalepipethreads shallbeprovided ateachpressure site and any other requirements specific to the tappreferably fora“6mmor 12mmthread forisolation operator. valve. Turning radius clearance shall be provided to allow a valve body to be screwed directly into the 5.1.2 Corrosion Resistance pressure tap. Pressure taps can be located at the top, Allwetted parts ofthe meter shallbemanufactured of Ietlside,and/orrightsideofthemeterbody. Additional materialscompatible withnaturalgasandrelatedfluids. taps may provide the designer with flexibility in Allexternal parts ofthe meter shallbe made ofanon- Iocating pressure transducers for maintenance access corrosive material or sealed with acorrosion-resistant and proper drainage of gauge line condensates back coating suitable foruseinatmospheres typically found into the meter body. inthe natural gas industry, andlor as specified by the 5.1.6 Miscellaneous designer. The meter shall be designed in such a way that the 5.1.3 Meter Body Lengths and Bores body will not roll when resting on a smooth surface The manufacturers should publish their standard with a slope of up to 10 percent. This is to prevent 3 I 1S15674:2006 damage to the protruding transducers and SPU when data, calibration method used and characterization the USM is temporari Iy set on the ground during parameter(s). installation or maintenance work. 7 ELECTRONICS The meter shall be designed to permit easy and safe handling of the meter during transportation and 7.1 General Requirements installation. Hoisting eyesorclearance forliftingstraps The USM electronics system, including power shall be provided. supplies, micro computer, signal processing I components and ultrasonic transducer excitation 6 ULTRASONIC TRANSDUCERS circuits, may be housed in one or more enclosures 6,1 General mounted as per the agreement between the supplier and theusers. Themanufacturers shallstatethegeneralspecifications of their ultrasonic transducers, such as critical Optionally,aremoteunitcontaining thepower supplies dimensions, maximum allowable operating pressure, and the operator interface may be installed in a non- operating pressure range, operating temperature range hazardous area and connected to the SPU by mtilti- and gas composition limitations. conductor cable. Themanufacturer shallspeci$ theminimumoperating The SPU shall operate over its entire specified pressure based on the ultrasonic transducer model, environmental conditions within the meter USM size and expected operating conditions. This performance requirements. It shall alsobe possible to minimum pressure shall be marked or tagged on the replacetheentire SPUorchangeanyfieldreplacement USM toalert the operator’s field personnel that the module withnut a.significant change in meter I meter may not register flow at reduced pipeline performance ‘Significant change’. pressures. The system shall contain a watch-dog-timer fhnction 6.2 Rate of Pressure Change toensure automatic restart ofthe SPU inthe eventofa program fault or lock-up. Sudden depressurization of an ultrasonic transducer maycause damage ifatrapped volume ofgasexpands The meter shall operate from a power supply of inside the transducer. If necessary, clear instructions nominal 120V a.c. or 240V a.c. at 50 Hz or from shall be provided by the manufacturer for nominal 12V d.c. or 24V d.c. power supply/batte~ repressurization and pressurization of the meter and systems, as per the agreement between the supplier transducers during installation, start-up, maintenance andthe user. and operation. 7.2 Output Signal Specifications It shall be possible to replace or relocate transducers The SPU shall be equipped with at least one of the without a significant change in meter performance. following outputs: This means that after an exchange of transducers and apo&ible change of SPU software constants directed a) serial data interface; and bythe manufacturer, the resulting shift inthe meter’s b) frequency, representing flowrate at line performance shall not be outside the limits of the conditions. pe~formance. The meter may also be equipped with an analog The manufacturer shall specify procedures to beused (4-20mA,.d.c.) output for flowrate at line conditions. when transducers have to be exchanged, andpossible Flowrate signalshallbescaleable upto 120percent of mechanical, electrical or other measurements and the meter’s maximum flowrate, q~,x. adjustments have to be made. Alow-flow cut-off timction shallbeprovided that sets 6.3 Transducer Tests the flowrate output to zerowhen the indicate flowrate Each transducer or pair of transducers shall be tested isbelowaminimumvalue(notapplicable toserialdata bythemanufacturer andtheresults documented aspart output). of the USM quality assurance programme. Each Two separate flowrate outputs and a directional state transducer shallbemarked ortagged withapermanent output or serial data values shall be provided for b~ serial number and be provided with the general directional applications to facilitate the separate transducer. If the SPU requires specific transducer accumulation of volumes by the associated flow characterization parameters, each transducer or computer(s) and directional state output signal. transducer pair shall also be provided with test documentation thatcontainsthespecificcalibrationtest Alloutputs shallbe isolated from.ground andhave the 4 IS 15674:2006 necessary voltage protection to meet the electronics to view andprint the flow measurement configuration design testing requirements. parameters used by the SPU; for example, calibration constants,meterdimensions,timeaveraging period and 7.3 Electrical Safety Design Requirements sampling rate. The design of the USM, including the SPU, shall be Provisions shall be made to prevent an accidenhl or analyzed, tested and certified by an applicable undetectable alteration ofthose parameters that affects laboratory, and then each meter shall be labelled as the performance of the meter. Suitable provisions approved foroperation inaNational Electric Codeand include a sealable switch or jumper, a permanent Hazardous Area, at a minimum. Intrinsically safe programmable read-only memory chip or a password designs and explosion proof enclosure designs are inthe SPU. generally certified andlabelled. Themanufacturer shall specify the more location requirement to achieve a 8.2.2 Optional Requirement more conservative installation design. It shall be possible for the auditor to veri~ that all Cablejackets, rubber, plastic and other exposed parts algorithms, constants and configuration parameters shallberesistant toultraviolet light,flames,andgrease. being used, in any specific meter, are producing the same or better performance as when the meter design 8 COMPUTER PRQGRAMMES was originally flow-tested or when the specific meter was last flow-calibrated and any calibration factors 8.1 Firmware were changed. The auditor may have to rely on the Computer codes responsible for the control and manufacturer for portions ofthis-verification because operation ofthe meter shallbe stored inanon-volatile of the proprietary nature of some USM algorithms. memory. All flow-calculation constants and the operator-entered parameters shallalsobestoredinnon- 8.3 Alarms volatile memory. The following alarm-status outputs shall be provided For auditing purposes, itshallbepossible to verify all inthe form of fail-safe, dry, relay contacts or voltage- flow-calculation constants and parameters which the free solid-state switches isolated from ground: meter is inoperation. a) Output Invalid when the indicated flowrate The manufacturer should maintain a record of all at line conditions isinvalim firmware revisions, including revision serial number b) Trouble (Optional): when any of several dateofrevision, applicable metermodels, circuitboard monitored parameters fall outside of normal revisions andadescription ofchanges tothefirmware. operation forasignificant period oftime; and The firmware revision number, revision date, serial c) Partial Failure (Optiona~: whenoneormore number and/or checksum shall be available to the of the multiple ultrasonic path results is not auditor by visual inspection of the firmware chip, usable, display or digital communications port. 8.4 Diagnostic Measurements The manufacturer may offer firmware upgrades from Themanufacturer shallprovide thefollowing andother time to time to improve the performance of the meter diagnostic measurements via a serial data interface. or add additional features. The manufacturer shall noti@the operator ifthe firmware revision will affect a) Average axial flow velocity through the the accuracy of aflow-calibrated meter. meter; The meter shall be supplied with acapability forlocal b) Flow velocity for each acoustic path (or or remote configuring of the SPU and for monitoring equivalent for evaluation of the flowing theoperation ofthemeter. Asaminimum,thesoftware velocity profile); shall be able to display and record the following c) Speed of sound along each acoustic path; measurements: flowrate at line conditions, mean d) Average speed of sound; velocity, average speed ofsound,speedofsoundalong e) Velocity sampling interval; eachacousticpathandultrasonic acousticsignalquality f-) Averaging time interval; received by each transducer. As an option, the ‘d Percentage of accepted pulses for each manufacturer may provide these software functions as acoustic path; part of the meter’s embedded software. h) Status and measurement quality indicators; 8.2 Inspection and Auditing Functions and 8.2.1 Itshallbepossible fortheauditorortheinspect or Alarm and failure indicators. 5