1、AN AMERICAN NATIONAL STANDARDASME MFC-8M2001FLUID FLOW IN CLOSED CONDUITS:CONNECTIONS FORPRESSURE SIGNALTRANSMISSIONS BETWEEN PRIMARY ANDSECONDARY DEVICESIntentionally left blank FLUID FLOW IN CLOSED CONDUITS: CONNECTIONS FOR PRESSURE SIGNAL TRANSMISSIONS BETWEEN PRIMARY AND SECONDARY DEVICESASME MF
2、C-8M2001AN AMERICAN NATIONAL STANDARDDate of Issuance: September 11, 2001This Standard will be revised when the Society approves the issuance of anew edition. There will be no addenda issued to this edition.ASME will issue written replies to inquiries concerning interpretations oftechnical aspects o
3、f this Standard.ASME is the registered trademark of The American Society of Mechanical Engineers.This code or standard was developed under procedures accredited as meeting the criteria forAmerican National Standards. The Standards Committee that approved the code or standardwas balanced to assure th
4、at individuals from competent and concerned interests have had anopportunity to participate. The proposed code or standard was made available for public reviewand comment that provides an opportunity for additional public input from industry, academia,regulatory agencies, and the public-at-large.ASM
5、E does not “approve,” “rate,” or “endorse” any item, construction, proprietary device,or activity.ASME does not take any position with respect to the validity of any patent rights asserted inconnection with any items mentioned in this document, and does not undertake to insure anyoneutilizing a stan
6、dard against liability for infringement of any applicable letters patent, nor assumeany such liability. Users of a code or standard are expressly advised that determination of thevalidity of any such patent rights, and the risk of infringement of such rights, is entirely theirown responsibility.Part
7、icipation by federal agency representative(s) or person(s) affiliated with industry is not tobe interpreted as government or industry endorsement of this code or standard.ASME accepts responsibility for only those interpretations of this document issued inaccordance with the established ASME procedu
8、res and policies, which precludes the issuanceof interpretations by individuals.No part of this document may be reproduced in any form,in an electronic retrieval system or otherwise,without the prior written permission of the publisher.The American Society of Mechanical EngineersThree Park Avenue, N
9、ew York, NY 10016-5990Copyright 2001 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll Rights ReservedPrinted in U.S.A.FOREWORDThis Standard is based on current industrial and research practices and was prepared bythe ASME Committee on Measurement of Fluid Flow In Closed Conduits (MFC).This Standard
10、 was approved as an American National Standard on May 24, 2001.iiiASME STANDARDS COMMITTEE MFCMeasurement of Fluid Flow In Closed Conduits(The following is the roster of the Committee at the time of approval of this Standard.)OFFICERSZ. D. Husain, ChairR. J. DeBoom, Vice ChairR. L. Crane, SecretaryC
11、OMMITTEE PERSONNELN. A. Alston, Daniel Measurement however, they should not contain proprietary names or information.Requests that are not in this format will be rewritten in this format by the Committeeprior to being answered, which may inadvertently change the intent of the original request.ASME p
12、rocedures provide for reconsideration of any interpretation when or if additionalinformation that might affect an interpretation is available. Further, persons aggrieved byan interpretation may appeal to the cognizant ASME Committee or Subcommittee. ASMEdoes not “approve”, “certify”, “rate”, or “end
13、orse” any item, construction, proprietary device,or activity.Attending Committee Meetings. The MFC Standards Committee regularly holds meetings,which are open to the public. Persons wishing to attend any meeting should contact theSecretary of the MFC Standards Committee.viCONTENTSForeword iiiCommitt
14、ee Roster ivCommittee Correspondence vi1 Introduction 12 Scope 12.1 1Field of Application 2.2 1References and Related Documents 3 General 13.1 1Containment .3.2 1Codes .3.3 1Specification Break .3.4 2Pressure Test .3.5 2Inspection 3.6 2Rod Out .3.7 2Valve Orientation 3.8 2Manifold .3.9 2Installation
15、 .3.10 3Valve Arrangement .4 Horizontal Piping Installations 34.1 3Gas .4.2 3Liquid .4.3 3Condensing Vapor 5 Vertical Piping Installations . 45.1 4Gas .5.2 4Liquids 5.3 4Condensing Vapor Service 6 Piezometer Ring . 47 Special Cases 47.1 4Pressure Taps 7.2 4Impulse Line Size 7.3 5Insulation Figure1 P
16、rimary and Secondary at Same Elevation, Preferred Installation 2viiNonmandatory AppendicesA Impulse Line Dynamics 7B Elevation Head Example Calculation 8C Supplemental Figures . 9viiiASME MFC-8M2001FLUID FLOW IN CLOSED CONDUITS: CONNECTIONSFOR PRESSURE SIGNAL TRANSMISSIONSBETWEEN PRIMARY AND SECONDA
17、RY DEVICES1 INTRODUCTIONThis Standard provides guidance in the design ofthe pressure signal connections between a flowmeterprimary device and the secondary device where theyare physically separate and connected by gauge linesor impulse piping. The primary device or flow elementcreates a pressure dif
18、ference or head at the pressuretaps, which is related to the flow rate. The secondarydevice may display and may convert and transmit theflow signal to another location.2 SCOPEThis Standard describes the practices and meanswhich allow the pressures at a head type primary deviceto be conveyed to the s
19、econdary device in a flowmeasurement system without introducing unnecessarymeasurement uncertainties.2.1 Field Of ApplicationThis Standard is concerned only with the transmissionof the pressure difference developed by a head typeprimary flow element. It does not address the characteris-tics of the p
20、rimary or secondary devices, or transducersor other instruments. Electrical transmission techniquesare not considered.2.2 References and Related DocumentsThe following is a list of publications referenced inthis Standard. Unless otherwise specified, the referencedstandard shall be the most recent is
21、sue at the time oforder placement.ASME Fluid Meters, Their Theory and Application,Sixth Edition, 1971ASME MFC-3M, Measurement of Fluid Flow in PipesUsing Orifice, Nozzle, and Venturi (not an AmericanNational Standard)1ASME PTC 19.2, Instruments and Apparatus: Part 2 Pressure MeasurementPublisher: Th
22、e American Society of Mechanical Engi-neers (ASME), Three Park Avenue, New York, NY10016; Order Department: 22 Law Drive, Box 2300,Fairfield, NJ 07007-23003 GENERAL3.1 ContainmentSafe containment of the fluid requires conformanceto the applicable standards and codes, and requires theselection of the
23、 proper materials of construction; thefabrication methods and practices; fittings; and anyrequired gaskets or sealing materials.3.2 CodesThe pipe or tubing installed between the primaryand secondary devices must comply with applicablerequirements such as national, local and owner codes,standards, an
24、d guidelines. The process piping specifica-tion determines the specifications for the block or thevalve closest to the primary element. The specificationsfor the piping between this valve and the secondarydevice, and any valves in this piping, may differ. Thesmall size, limited flow, and often the m
25、ore limitedtemperatures involved, justifies these differences (seeFig. 1).3.3 Specification BreakThe break (change) in piping specifications betweenprocess and the secondary or instrument side is normallyat the secondary end connection of the process valve(see Fig. 1). If the process piping specific
26、ation requiresflanged connection, then the process end of this valveFLUID FLOW IN CLOSED CONDUITSASME MFC-8M2001Conduit running fullSpecification break, wherethe piping specificationschange between primary andsecondaryPrimary sideSecondary sidePrimary head creating deviceIsolation valvesManifoldSeco
27、ndary deviceBleed valves, typicalAlternate location for manifoldImpulse line, connection pipingFIG. 1 PRIMARY AND SECONDARY AT SAME ELEVATION, PREFERRED INSTALLATIONis flanged and the mating flange on the secondaryside is an instrument connection or may have anotherapproved fitting.3.4 Pressure Test
28、An approved hydrostatic pressure test may be requiredfor piping systems to prove the integrity of the pressurecontaining parts of the piping system.3.5 InspectionA visual inspection of each installation is recom-mended for adherence to safety and measurement re-quirements before putting each flowmet
29、er into operation(see MFC-3M). Install primary per manufacturer instruc-tions.3.6 Rod OutSome installations will require provision for roddingout of the process connections. This is the use of arod or other physical device to remove materialsblocking the free flow of fluid into the impulse lines.Obs
30、erve the applicable safety precautions.3.7 Valve OrientationGlobe style block valves may create a pocket of gasor liquid if they are installed with the stem in thevertical orientation. This pocket may result in a pressuredifference and an error in the indicated measurement.Installation with the stem
31、 at an angle of 90 deg from2the vertical normally solves this problem. Ball valvesand gate valves do not have this problem.3.8 ManifoldValves are often installed to permit calibrating thesecondary device without removing it. These are usedto block the impulse pressure lines from the primarydevice an
32、d to open a path between the high and lowsecondary device pressure taps. Where specified, twoadditional valves are installed to allow draining orventing of the impulse piping to the atmosphere ordrain. The secondary device zero, or no flow signal,can be adjusted at operating pressure with one blockv
33、alve closed and the bypass valve open. Manufacturedvalve manifolds may reduce cost and save space. Mani-folds integrate the required valves and connections intoone assembly and have connection spacing compatiblewith orifice flanges and the standard secondary devices.(see Fig. C1). Install manifolds
34、in the orientation speci-fied by the manufacturer to avoid possible errors causedby pockets of trapped gas or liquid in the body.3.9 InstallationThe preferred design will minimize the separationbetween the primary and secondary devices. In someinstallations, the isolation valves and the bypass mani-
35、fold are omitted. As an alternative (see Fig. 1), thebypass manifold may be installed to the back connec-tions of the secondary to further reduce fittings andobstructions to pressure signal flow. The connectingFLUID FLOW IN CLOSED CONDUITS ASME MFC-8M2001piping is variously referred to as impulse li
36、nes, gaugelines, instrument tubing,orinstrument piping.The detail design for the installation of the flowmetersecondary system should consider instrument trouble-shooting and calibration. Access to the impulse lines, thevalves, manifold and the secondary device is required.Installations providing th
37、is access must not compromisethe measurement accuracy by adding excessive pressuresensing lines and fittings. Longer and more complexpiping may increase uncertainties and provide moreopportunity for plugging. Plugged lines lead to loss ofcontrol and may create hazardous situations.Any difference in
38、elevation between the primarydevice pressure taps and the secondary will result ina pressure difference between the two ends. If thefluids in the two lines are not identical in density, adifference in pressure is generated. Density differenceswill arise if there is a temperature difference betweenth
39、e fluids in the two impulse lines. (See Appendix Bfor an example of a typical calculation.) It is recom-mended that the two impulse lines are fastened togetherand, if insulated, they are insulated together. Non-identical fluids in the two impulse lines can also giverise to density differences.It is
40、also recommended that, where allowable, thesecondary be “bled” or “vented” after installation toclear the impulse lines of fluids left during the construc-tion or after hydrostatic testing or system cleaning.Bleed valves may be included in manifolds or in thesecondary device body, or installed as ne
41、eded.Periodic bleeding may be required if the characteristicsof the fluids in the impulse lines change over timewith fluid aging and with diffusion or leakage into orout of the impulse lines.The general experience in industry is that dirt iseverywhere, and that liquids will have entrained orcondense
42、d liquids. It is good practice to design theinstallation to allow for natural draining of liquids orventing of gases.3.10 Valve ArrangementWhere the primary device uses flange taps in thesmaller size pipes, it is likely that block valves andflanges will physically interfere with each other if theyar
43、e mounted directly in line with the primary devicepressure taps (see Fig. C2). In vertical lines, alternateflange taps can be used to avoid mechanical interference;but this practice is not encouraged. Vertical flow installa-tion of head type meters in vapor service is discouraged.34 HORIZONTAL PIPIN
44、G INSTALLATIONS4.1 GasPressure taps on the primary element shall be onthe horizontal centerline or up to the top of the pipeunless the measured fluid is a vapor which is intendedto condense in the secondary system (see para. 4.3).Liquids or condensate must be free to flow down andout of the measurem
45、ent system (see Fig. C3). Therecommended slope for self draining is a minimum of1in12.4.2 LiquidPressure taps shall be on the horizontal centerline.Taps below the centerline may accumulate solids; tapsabove the centerline will accumulate air or non-condens-able gases. In liquid service, the connecti
46、ng lines fromthe primary device shall slope downward to the second-ary with no up turns or pockets (see Fig. C4). Gasbubbles must be free to flow up and out of themeasurement system. The recommended slope for selfventing is a minimum of 1 in 12.4.3 Condensing VaporThe pressure taps shall be on the h
47、orizontal centerlineof the primary device. In condensing hot vapor service,such as steam, the fluid in the impulse lines is liquidcondensed from the vapor. Follow the arrangementrequirements for liquids with the secondary devicebelow the primary (see Fig. C4). Cryogenic (very lowtemperatures) system
48、s may require special designs. Theliquid in the lines will isolate the secondary devicefrom the temperatures of the primary flowing fluid.The temperature difference may be considerable overa short distance of 100 mm to 200 mm (4 in. to 8 in.).There is a concern that at startup the secondarydevice co
49、uld be exposed to the vapor temperature beforethe lines fill with condensate and cool. A plugged teefitting in the impulse line will permit filling the impulsetubing and secondary with water (for steam service)before startup (see Fig. C5).Where permitted, this problem may be mitigated bya careful commissioning procedure slowly filling thesystem and allowing sufficient time for pressure trans-mitting lines to condense vapors.FLUID FLOW IN CLOSED CONDUITSASME MFC-8M20015 VERTICAL PIPING INSTALLATIONS5.1 GasIn noncondensing service (see para. 4.1), the con-necting lines from the primary
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