IACME MFC-6M-1998 A N AMERICAN NATIONAL STANDARD The American Society of Mechanical Enoinee rs Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale, 03/31/2005 17:15:12 MST --`,,```,`,,````,`,`,`,,``,,`,,-`-`,,`,,`,`,,`--- MEASUREMENT OF FLUID FLOW N I PIPES USING VORTEX FLOWMETERS `.`..`.....`.`...4 The American Society of Mechanical Enaineen A M E R I C A N N A T I O N A L S T A N D A R D MEASUREMENT OF FLUID FLOW N I PIPES USING VORTEX FLOWMETERS ASME MFC-6M-1998 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.````. 03/31/2005 17:15:12 MST --`.`.-`-`.`.`.``.`--- A N ..```. in an electronic retrieval system or otherwise." or "endorse" any item. There will be no addenda or written interpretations of the requirements of this Standard issued to this edition.A. or activity.`.`. Participation by federal agency representative(sl or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard. ASME does not "approve.. Users of a code or standard are expressly advised that determination of the validity of any such patent rights. construction.```.`.``.`.STDmASME MFC-bM-ENGL 1998 I0759670 Ob04052 438 Date of Issuance: July 4. ASME accepts responsibility for only those interpretations issued in accordancewith governing ASME procedures and policies which preclude the issuance of interpretations by individual volunteers." "rate. New York. proprietary device.. 1998 ASME is the registered trademark of The American Society of Mechanical Engineers.. and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable Letters Patent. Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.-`-`.S. . ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document. The proposed code or standard was made available for public review and comment which provides an opportunity for additional public input from industry. without the prior written permission of the publisher. The Standards Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an opportunity to participate.. nor assume any such liability. and the risk of the infringement of such rights.`. No part of this document may be reproduced in any form.`--- This Standard will be revised when the Society approves the issuance of a new edition. 03/31/2005 17:15:12 MST --`. . regulatory agencies.`.`. The American Society of Mechanical Engineers Three Park Avenue. academia. This code or standard was developed under procedures accredited as meeting the criteria for American National Standards.````. NY 10016-5990 Copyright CP 1998 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.... and the public-at-large.. is entirely their own responsibility.`. Vortex shedding flowmeters are also referred to as vortex meters.`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.(This Foreword is not a part of ASME MFC-6M-1998. This Standard was approved by the American National Standards Institute on February 20.``.`.`.````. their design details and associated uncertainty bands cannot be covered in this document. The vortex pairs can be counted over a given period of time to obtain total flow.Vortex Shedding Flowmeters. these devices have in common the shedding of alternating pairs of vortices from some obstruction in the meter. flow of fluids in closed conduits. and equations with which to determine the expected performance characteristics.`.. Meters based on this principle are available for measuring the flow of fluids ranging from cryogenic liquids to steam and high-pressure gases.. 1998. application notes. 03/31/2005 17:15:12 MST .`. f.-`-`.. therefore. test procedures. This Standard contains the relevant terminology...```. iii --`. qv.`.`..) This Standard has been prepared by ASME/MFCC/SC16 ..`. of the fluid in the conduit.`. Their designs are proprietary and. to the volumetric flowrate. The natural laws of physics relate the shedding frequency. However. The vortex shedding principle has become an accepted basis for fluid flow measurement. list of specifications.. It is one of a series of standards covering a variety of devices that measure the. G.`. Keyser. G. E.. Inc. Kansas City. Vice Chair K. Dow Chemical D. Inc. Inc. Nelson. P. M. Storer. Ford Motor Co. Colorado Engineering Experiment Station. Foxboro Co. Missouri Water & Pollution Control Department W. Vignos. H. W. G. Mahieu. Secretary COMMITTEE PERSONNEL N. D. Saudi Aramco T. R. Fritz. H. Williamson. Ullrich. P. D. R. Miller. Turnbow Engineering 2.`. SUBCOMMITTEE 16 PERSONNEL W. Inc.`--- R. Jones. Chair. McHale & Associates. Nepera Inc. Husain. Hiilburn.W. C.`. Inc.ASME STANDARDS COMMITTEE MFFCC Measurement of Fluid Flow in Closed Conduits (The following is the roster of the Committee at the time of approval of this Standard. Inc. Preso Industries S. R. M.. T.. DeBoom. Vignos. M. Corpron. Jones. Miller. Wyatt. E. A. J. R. D. Caron. Inc. E.`.`. Primary Flow Signal. J. Equimeter. W. H.`. H. Micro Motion. Mattar. Skweres. Consultant W.`. Chair E.-`-`. A. Badger Meter. W. Inc. NAWC C.. McHale. Wiklund. Padilla. H. J. P. H. Strobel.`. Nepera Inc. Department of Commerce P. Alston. Barnant Co. Inc. M. D. A. D. Mattingly. Equimeter. Inc. Texaco.. Skweres. E. D. Dow Chemical D. C.F. Foxboro Co.S. Spitzer. Colorado Engineering Experiment Station. Mattingly. H. V Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale. DeBoom. W. E. 03/31/2005 17:15:12 MST . U. Kegel. Ford Motor Co.. Micro Motion.. G. M. S.``. Langford. Mattar. R.) OFFICERS --`. Inc. Inc.```. Nova Research & Technology Corp. Foxboro Co. Measurement & Control. Kegel. Chevron Petroleum Technology T. Seidl.````. R. Inc. I. Rocemount. J. P. G. Blechinger. Consultant J. Rosemount. Corpron. L. Colorado Engineering Experiment Station. Inc. Miller & Associates J.Spitzer. Department of Commerce M. Taha. R. Vortek Instruments J. US. Wiklund. J. W. W.. Foxboro Co. .......`..................... 7....4 New Installations ......... 6..1 Physical Components .. 1 3 Definitions .......`.................1 Sizing ....```.............................................. 6 7 7 7 7 8 Operation ........................................ 6.................... 1 2 References and Related Documents .......................................................................................... 5 Application Considerations ............. 7................................ 4 Table 1 Symbols 2 Factor Determination ....................``..........................................2 Flowmeter Orientation .......`..... Committee Roster ..`.............................................................................................................................2 Equipment Markings ....................................................................................... 4 5 Flowmeter Description ..................3 Safety .... 5..................... 5 5 6 6 7 Installation ......2 Process Influences ..............................................................3 Flowmeter Location .................................................. ...................................`................................................................................................................................................................................`............ 03/31/2005 17:15:12 MST 3 9 ......CONTENTS Foreword .`................................................................`.........................................-`-`........... 7.................................... 111 v 1 Scope .....1 Adjacent Piping ............................. 6.................................... 7................... 1 4 Principle of Measurement ...................................................................................................................................... Appendix A Period Jitter and Its Effect on Calibration .......````.......... 7 9 K 6 5 5 . --`............................. 5.... 2 Vortex Formation ............................................................`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale................................................................ 7 Figures 1 Example of a K Factor Curve .................... . Expressions of the Functional Performance of Electronic Measuring Equipment IEC PUB 381-1 d. mass.Flowrate Measurement by Means of Ultrasonic Flowmeters Publisher: International Organization for Standardization (ISO)..ASME MFC-6M-1998 MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS This Standard: (a) describes vortex shedding flowmeters in which alternating vortices are shed from one or more bluff bodies installed in a closed circular conduit. If) addresses phenomena that may negatively affect vortex detection. 2 REFERENCES AND RELATED DOCUMENTS Unless otherwise indicated. Method for Establishing Installation Effects on Flowmeters Publisher: The American Society of Mechanical Engineers (ASME).Vocabulary and Symbols IS0 4185. (6) describes how the frequency of the vortex pairs is a measure of the fluid velocity. (c) applies only to fluid flow that is steady or varies only slowly with time.```.`. CH-1211 Genevé 20. ASME MFC-lM. and (g) provides calibration guidance. is considered single-phased.. Glossary of Terms Used in the Measurement of Fluid Flow in Pipes ASME MFC-2M. and material traceability. the following definitions are particularly useful in describing the Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.c.`. i rue de Varembé. Assessment of Uncertainty in the Calibration and Use of Flow Measurement Devices .Weighing Method IS0 5168. Three Park Aienue.. and how the total fluid that has Rowed through the meter in a specified time interval can be measured. as well as shift the K factor.Method by Collection of the Liquid in a Volumetric Tank IS0 DIS 9368. how volume. NY 10016-5990 - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS IS0 4006.10M.. Switzerland 3 DEFINITIONS (See Table 1 for Symbols) For the purposes of this Standard.``.. Switzerland IEC PUB 359. and when the closed conduit is full. and describes guidelines for reducing or eliminating their influences.`..c. CH121I Genevé 20. the latest issue of a referenced standard shall apply. Installations for Flowrate Measurement by the Weighing Method .`. Ingress Protection Classification and Testing Procedures Publisher: International Electrotechnical Commission (IEC).Test Methods .Part 1: Linear Calibration Relationships IS0 7066-2.````. Case postale 131.`. Current Transmission IEC PUB 381-2 d.Part 1: Static Weighing Systems IS0 TR 12764. 03/31/2005 17:15:12 MST --`. Measurement of Liquid Flow in Closed Conduits . Measurement of Fluid Flow in Closed Conduits .`. (e) describes the physical components of vortex shedding Rowmeters and identifies the need for inspection. Measurement Uncertainty for Fluid Flow in Closed Conduits ASME MFC-’IM. Measurement of Fluid Flow . Measurement of Fluid Flow in Closed Conduits . (d) provides only generic information on vortex shedding flowmeters. 3 rue de Varembé... Measurement of Liquid Flow in Closed Conduits by Weighing Method ASME MFC. including a glossary and a set of engineering equations useful in specifying performance. Measurement of Fluid Flow in Closed Conduits . certification.`--- 1 SCOPE .`. and standard volume flowrate is determined. Measurement of Gas Flow by Means of Critical Flow Venturi Nozzles ASME MFC-9M.Flowrate Measurement by Means of Vortex Shedding Flowmeters Inserted in Circular Cross-Section Conduits Running Full IS0 DTR 12765.Evaluation of Uncertainty IS0 7066-1. New York.Part 2: Non-Linear Calibration Relationships IS0 8316.. Case postale 56. Voltage Transmission IEC PUB 529.-`-`. Measurement of Fluid Flow in Closed Conduits .`. Assessment of Uncertainty in the Calibration and Use of Flow Measurement Devices . `.`--- refers to reference condition i i = volume units..`....````. reference conditions v = mean = max = min = i= volume units. flowing conditions average of extreme values maximum value minimum value the ith measurement dmin= minimum downstrean value 2 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS m3/s K-1 r1 GENERAL NOTES: (a) Fundamental dimensions: M = mass..`. see above rn = mass unit O = SI Units Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale. L = length.`. 03/31/2005 17:15:12 MST Pa Pa .`.``.```.`.`. 0 = temperature (b) Subscript: b = base conditions flow = flowing fluid conditions D = unobstructed diameter of meter bore....`.-`-`.STD=ASME MFC-bfl-ENGL 1998 m 0359b30 Ob04053 T I T m MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS ASME MFC-6M-1998 TABLE 1 SYMBOLS Symbol Quantity a Dimentions Averaging Time Diameter of meter bore Cross-sectional area of meter bore Frequency of vortex shedding Width of bluff body normal to the flow K factor Number of vortex pulses Volume flowrate Mass flowrate Totalized volume flow Totalized mass flow Reynolds number Strouhal number Average fluid velocity in meter bore Coefficient of linear expansion of material Absolute viscosity (dynamic) Fluid density Temperature % Error in the average period Two-tailed Student‘s t a t 95% confidence Estimate of standard deviation of the average period Average period of vortex shedding Number of period measurements Pressure Minimum downstream pressure limit Empirical constant Overall pressure drop Liquid vapor pressure at the flowing temperature D A f d K N 4 V 4m Q” Qm Re St U a P P T s t l7 7 n P Pdrnin c1I ci AP Pvsp T L S m L2 r1 Hr L m m-3 L-3 dimensionless L~ r1 M T’ 13 M dimensionless dimensionless Lrl 6’ ML-l MLJ kds m3 kg m/s Pds kg/m3 “K e dimensionless dimensionless T S T dimensionless ML-’ r2 S ML-l r2 Pa Pa dimensionless ML-l ML-l r2 r* --`. T = time. response time is the time needed for the indicated flowrate to differ from the true flowrate by a prescribed amount (e.```.. lowest local pressure: the lowest pressure found in the meter.``. Variations in the K factor may be presented as a function of either the meter bore Reynolds number or of the flowrate of a specific fluid at a specific set of thermodynamic conditions (see Fig. and analytical concepts pertaining to measurement uncertainty. which is not dimensionless.. defined either by ReD or qv of a specific fluid at specific thermodynamic conditions (see Fig. In equation form it is defined as: linearity: st =f x d U - In practice the K factor.. cavitation: jashing: Note: Ir is not possible to correct for random error --`.`. pressure loss: the formation of vapor bubbles in a liquid when the local pressure falls to or below the vapor pressure of the liquid.`. 10%).. the implosion of vapor bubbles formed after flashing when the local pressure rises above the vapor pressure of the liquid. which is defined by: component of uncertainty associated with a random error.. in the course of a number of measurements of the same measurand. the K factor that is commonly used is the mean K factor.````. density.A S f l E MFC-bfl-ENGL 1998 m 0759670 Ob04058 956 m MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS ASME MFC-6M-1998 The upper and lower limits of the linear range are specified by the manufacturer..`. 03/31/2005 17:15:12 MST .g. and pipe line velocity. statistical techniques. the Strouhal number is a dimensionless parameter that relates the measured vortex shedding frequency to the fluid velocity and the bluff body characteristic dimension. rundum error: component of the error of measurement which.S T D . often due to local lowering of pressure because of an increase in the liquid velocity. varies in an unpredictable way.`. the difference between the upstream pressure and the pressure downstream of the meter after recovery. It is given by: Strouhal number: where KmaX= the maximum K factor over a designated range Kmin = the minimum K factor over the same range linearity relates to the variations of the K factor over a specified range. random uncertainty: rangeability: flowmeter rangeability is the ratio of the maximum to minimum flowrates or Reynolds number in the range over which the meter meets a specified uncertainty (accuracy). IS0 7066-1 and IS0 7066-2 provide additional definitions. ASME MFC-1M provides a more extensive collection of definitions and symbols pertaining to the measurement of fluid flow in closed conduits. 3 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS (4) Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale. It is defined as: characteristics of vortex shedding flowmeters. i). This is the pressure of concern regarding flashing and cavitation. response time: for a step change in flowrate.. Some of the pressure is recovered downstream of the meter.-`-`. is the ratio of the meter output in number of pulses to the corresponding total volume of fluid passing through the meter during a measured period.`. 1 EXAMPLE OF A K FACTOR CURVE meter bore Reynolds number: the meter bore Reynolds number is a dimensionless ratio of inertial to viscous forces which is used as a correlating parameter that combines the effects of viscosity.`.. in pulses per unit volume. Its effect on mean values can be reduced by taking many measurements.`.. ReD = meter factor: DUP CL (3) the reciprocal of mean K factor. In practice.`.`--- K factor: the K factor. i). Either ReD or qv of a specific fluid at specific thermodynamic conditions FIG. the bluff body characteristic The K Factor for a vortex shedding flowmeter is related to the Strouhal number by: Hence. the Strouhal number remains essentially constant within a large range of Reynolds numbers.``. d. 2). can be determined. The frequency at which pairs of vortices are shed is directly proportional to the fluid velocity.`. This series of vortices is called a von Karmanlike vortex street (see Fig. a boundary layer forms and grows along the surface of the bluff body. Due to insufficient momentum and an adverse pressure gradient.. Le. and the volumetric flowrate at flowing conditions. remains constant or varies in a predictable way. is given by: Note: Uncertainty is also referred to as accuracy.`. 10) and the volumetric flowrate at base conditions..`..-`-`. This means that the Suouhal number is independent of density. For certain bluff body shapes. the volume flowrate. Le.e.`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS f K Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.`.. 4 PRINCIPLE OF MEASUREMENT (7) If a bluff body is placed in a pipe in which fluid is flowing. the mass flowrate (see Eq. Noie: Systematic errors and their causes may be known or unknown. standard volume flowrate (see Eq. pressure. U. 2 VORTEX FORMATION dimension. and other physical parameters.`.. separation occurs and an inherently unstable shear layer is formed. in the course of a number of measurements of the same measurand. viscosity.. 4 --`. Le.`... relates the frequency. and the fluid velocity. systematic uncertainty: uncertainty: an estimate characterizing the range of values within which the true value of a measurement lies.... of generated vortex pairs.`. where 5 is a constant equal to %. This shear layer rolls up into vortices that shed alternately from the sides of the body and propagate downstream. Its effect cannot be reduced by taking many measurements. The Strouhal number.`. ¡.MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS ASME MFC-6M-1998 Shear layer 1 r r Bluffbody Conduit FIG. sysrernatic error: a component of the error of measurement which. to convert the pressure or velocity variations associated with the vortices to electrical signals.f. Sensors are used to detect shedding vortex pairs. replaces the Strouhal number as the significant parameter. a component of uncertainty associated with a systematic error. i l ) . Given this situation. Since the shedding process is repeatable it can be used to measure flow. the flow velocity is directly proportional to the frequency at which the vortex pairs are being shed.````.. St. 03/31/2005 17:15:12 MST . 4" = (9) When the density at flowing temperature and pressure is known.```.. the vortex pulse rate. mean K factor. over that time interval. but the three primary ones are sizing. Pressure loss increases with flowrate but is usually not the limiting factor in sizing a vortex flowmeter. These limits vary by manufacturer.````. ( b ) a digital total flow readout. (c) a pulse or scaled pulse signal. The bluff body is the shedding element positioned in the cross-section of the meter body. The direction of flow shall be permanently indicated by the manufacturer on the meter body. 5. The sensor detects the shedding vortices (see Section 4).`.-`-`.1 Physical Components The vortex shedding flowmeter consists of two elements: the flowtube and the transmitter. Figure 2 shows it as a square cross-section bluff body.. pressure rating. Assuming further that the fluid density remains constant over the measurement time interval. if any. process influences. The flowtube is made up of the meter body. pressure loss resulting from the flowmeter and the associated connections must be considered in system design. over one cycle of period T . or Meter factor. frequency. However. the amount of fluid volume that flows through the meter during one cycle is: 5. or (d) a current proportional to flowrate.. and safety. = rf) x Size the meter according to the desired flow range rather than the nominal pipe size..1. Since K is a constant independent of the flowrate and.STDmASME MFC-bM-ENGL 0759630 Ob04060 504 1998 MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS qv= ACME MFC-6M-1998 intended to imply a preferred shape. If used outside the stated Reynolds number range.`.``. Its shape and dimensions and the ratio of the frontal area in relation to the open area in the meter body cross-section influence the linearity of the K factor..e. the total flow over N cycles is: N Qu =- K where N is the total number of vortex pairs shed.1 Maximum Flow.`. total number of vortex pulses. except possibly in low pressure applications.```.e. ¡.`--- and Q.1 Flowtube. serial number. 5. :i) K - x- 5. Sensor technology and location vary with flowmeter design.2 Transmitter.. N K 5 FLOWMETER DESCRIPTION 6.. then 6 APPLICATION CONSIDERATIONS There are several considerations related to application of vortex meters..`. The flowmeter size shall be selected such that the expected process flowrate falls between the maximum and minimum flowrates within the required uncertainty. the bluff body(s). The maximum flow for a vortex meter is usually limited by the structural integrity of the device.`. I). and the sensor. The transmitter converts sensed signals to one or more of the following: (a) a digital flowrate readout.2 Equipment Markings Meters shall be marked by the manufacturer to identify the manufacturer. hence. The minimum volumetric flowrate depends on the Reynolds number (see Fig..1.2 Minimum Flow. but this is not 6.1. the manufacturer should be consulted for details regarding correction procedures and the expected magnitude of the measurement uncertainty. and hazardous location certification. Assume that the flowrate can be considered constant over the time it takes a vortex pair to shed. 6.`. As the volumetric flowrate i s reduced 5 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.. In this case..1 Sizing --`.`.1. ¡.`. 03/31/2005 17:15:12 MST . The meter body is normally available in two styles: a flanged version that bolts directly to the flanges on the pipeline and a wafer version that is clamped between two adjacent pipeline flanges via bolts. The minimum volumetric flowrate may also be limited by the sensor(s). below a certain value for a given fluid density.1 Mechanical. The manufacturer’s installation instructions should be consulted regarding installation effects. In a liquid. The following 6 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.3 Flashing and Cavitation.2. are the responsibility of the user. and hence depends on temperature and pressure. 6. To handle this situation. and hence.`--- 6. The fluid stream should be steady or slowly varying.2. affect the K factor of the meter.2.`.. Measurement accuracy is directly related to K factor uncertainty. and fluid viscosity. this can lead to flashing and cavitation.1 Temperature and Pressure 6.3.`. Operation under conditions of flashing andi or cavitation is beyond the scope of this Standard. The Reynolds number is a function of geometry. The watertightness and hazardous area certification shall be suitable for the intended location. many designs may employ a low flow cutoff point where the meter output is automatically set to zero regardless of whether there is flow in the pipe or not. Requirements for specific location.3.1.3a x (TI- To)] To avoid flashing and cavitation. material traceability. The K factor. Process pressure effects on the K factor are generally negligible. the manufacturer should be contacted for the values of cl and c2.````.`... 6. The fluid density depends on the process temperature and pressure. 6. 6. as described in para.`. 03/31/2005 17:15:12 MST . 7 INSTALLATION Adjacent piping. Pulsations in flowrate or pressure may affect flow measurement. etc.. See IEC PUB 529 (Ingress Protection). it is essential that the instrument be designed and manufactured to meet or exceed industry standards for piping codes. Since vortex flowmeters are an integral part of the process piping (in-line instrumentation). The manufacturer should be consulted for information and relevant correction procedures regarding a specific flowmeter. cleaning requirements. flowmeter Orientation and location may affect flowmeter perforrnance.1. When the bluff body and the meter body are made of the same material. 6.`.```.. depends from a practical viewpoint only on the process temperature. fluid flow disturbances.`.2 Affect on Range. the change in K factor for a given change in temperature is estimated by: K = KOx [I .c2 = empirical constants for each design and size (15) When the bluff body and the meter body are made of different materials. piping codes.(2al+a*)x (q-To)] Because the pressure reduction is dependent on the construction of the meter. 6. fluid density.1.1 Affect on Uncertainty.``.2. Local lowering of pressure occurs when the fluid velocity is increased by the reduced cross-section around the bluff body of the meter.3 Safety 6.MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS ASME MFC-6M-1998 --`. the downstream pressure after recovery must be equal to or greater than Pdmin as given by: where Pdmin= minimum allowable downstream pressure after recovery Pvap= vapor pressure of the liquid at the flowing temperature AP = overall pressure drop CI.2..2 Flow. The range of a vortex meter depends in general on the following parameters: the K factor. and Reynolds number. Process temperatures that differ significantly from those during calibration can affect the geometry of the flowtube.`.2. the change in K factor for a given change in temperature is estimated by: K = K O x [i . (16) where a l = the thermal expansion coefficient of the meter body material cc2 = the thermal expansion coefficient of the bluff body material 6..-`-`.1.2 Electrical.2 Process Influences Note: Hashing and cavitation can lead to measurement errors and/ or structural damage.. The manufacturer should be consulted for specific information regarding these effects. fluid density.`. nondestructive evaluation (NDE). the vortex shedding weakens to the point at which the sensor can no longer distinguish between the vortex signal and noise due to flow or vibration. or density.`..`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale. Pipe reducers may be used upstream and downstream to install such flowmeters. 7. etc.. adjustment of the K factor a n d or uncertainty must be made. (b) The flowmeter must be mounted concentric with the pipe according to the manufacturer’s recommendations. and insufficient signal shielding may also interfere with the measurement. 7. or other pipeline debris. The manufacturer’s recommended startup procedures should be followed to avoid damage to the bluff body(s) or sensor(s) by overrange. The minimum lengths of straight pipe required to obtain the specified accuracy at operating conditions differ depending on flowmeter construction and the nature of the piping configuration. One way to ensure this is to install the meter in a vertical pipe with the flow upwards..4 New Installations New installations require that the line be cleaned to remove any collection of welding beads.`. It is usually good practice to remove the flowmeter before cleaning and prior to pressure testing for leaks.. its sizing and its location relative to the flowmeter. water hammer. temperature.```. 03/31/2005 17:15:12 MST . Common mode electrical noise may interfere with the measurement.~ STD=ASME MFC-bM-ENGL 1998 0759670 Ob04Qb2 387 I MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS are some of the factors to be considered.``. RFI (radio frequency interference).. improper grounding (earthing). The meter manufacturer should be consulted regarding the use of flow conditioners. The manufacturer should be contacted for advice if it is suspected that any of these noise levels is high enough to cause an error. an appropriate flow conditioner or acceptance of higher uncertainties. 7. pipe fittings. EM1 (electromagnetic interference).`. a meter size smaller than the pipe size may have to be used. the joined pipe should be straight. (c) Gaskets must not protrude inside the pipe. (d) The flowmeter should be mounted with straight runs of pipe upstream and downstream. 7. may impact the performance of a vortex flowmeter. Welding rings should be avoided within the required number of straight pipe lengths. If a bypass is installed to facilitate this. ( h ) In order to satisfy the minimum measureable flow requirement. In some cases it may not be possible to check the noise in the output signal with no flow. ( g ) The location of additional process measurements. and other process control elements. ( j ) When a particular meter installation is expected to deviate from the manufacturer’s recommendations. In liquid flow measurement the pipe must be flowing full.. the fittings must ASME MFC-6M-1998 be ahead of the upstream straight length of pipe or flow conditioner and beyond the downstream straight section.`. The straight runs should be free of changes in pipe size or schedule. such as pressure. Flowmeters should be installed with the orientation recommended by the manufacturer.-`-`. The flowmeter manufacturer’s literature should be consulted for recommendations.1 Adjacent Piping A vortex meter is sensitive to distorted or undeveloped velocity profiles and swirl caused by changes in pipe size or schedule and flow through pipe fittings. 9 K FACTOR DETERMINATION The meter manufacturer shall supply the meter’s mean K factor and the expected uncertainty under --`. Pipe schedule should be the same as that of the pipe used in calibration unless appropriate corrections are applied. (i) In some applications it may be desirable to periodically inspect and/or clean the flowmeter.`. valves. (e) If more than one pipe section is used within the minimum length of straight pipe. Ifl The required length of straight pipe may be reduced through the use of known correction factors.`. When pipe reducers are installed without sufficient straight length of pipe. valves and other internal obstructions.. la) The diameter of the adjacent pipe should be the same nominal diameter as the flowmeter.````. The valve(s) used to shut off main flow should be positive closing. Procedures for eliminating these effects are as follows..3 Flowmeter Location The flowmeter shall be properly supported to reduce any effects of vibration and pipe stress.`.`. the user may desire to perform in situ calibration. 8 OPERATION Flowmeters shall be operated within the manufacturer’s recommended operating limits to achieve the stated uncertainty and normal service life. with minimal misalignment. This includes the type of flow conditioner. rust particles.2 Flowmeter Orientation Proper orientation of the flowmeter in the pipe may depend on the nature of the fluid. 6.. or volumetric techniques are used.`. it is possible..`. (d) The K factor depends upon geometric changes in the meter body produced by temperature and pressure on the meter material (see para.````. 03/31/2005 17:15:12 MST .`..```.2).`. to derive the factor from dimensional measurements.`.`--- 8 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.`. or critical flow nozzles. The following considerations apply: ( a ) The mean K factor is usually established by flow calibrations with a suitable fluid. The method employed must be stated. weighing. For liquid flows. ( b ) Where possible.. volumetric tank with pressure and temperature corrections. --`. measurement uncertainty can be improved by in situ calibration. ( c ) All calibrations should be performed according to acceptable standards (see Section 2)..MEASUREMENT OF FLUID FLOW IN PIPES USING VORTEX FLOWMETERS ACME MFC-6M-1998 stated reference conditions and provide a certificate of calibration on request. the reference flow measurement device is usually a transfer device.`. but at reduced accuracy. For gas flows..-`-`. transfer..``..`. Once u has been determined. if severe. They range from the physical phenomena on which the measurement depends to the electronic signai processing techniques used to process the basic measurement.```.`.E N G L 1998 P1 0 7 5 9 b 7 0 Ob04064 L 5 T APPENDIX A . increasing that number would no longer significantly affect the standard deviation. period) between vortices to vary in a manner called “period jitter. 9 --`.. There are several influences that affect the vortex shedding characteristics of flowmeters..5 where where T = st si - = .Strouhai number U f = vortex shedding frequency U = flow velocity in the meter bore n t = student’s t with n-1 degrees of freedom for a d = width of the face of the bluff body(s) normal to the flow 95% confidence level (equal to 2. random variations may occur in the vortex shedding period from one cycle to another even though the flowrate is held constant.`.b l . The meter manufacturer should be contacted if vortices can differ from their mean values. Amplitude variations. is given by: Note: Period jitter and the associated frequency jitter is of no concern for most applications.-`-`. As a result. this “noise” causes the time (Le. a = N x is related to the flowrate by: N x d or equivalently 100xtxa 7 (ny3. particularly at low Rowrates.... Frequency jitter can affect the response time of a the turbulence level is such that it causes concern about these phenomena.`. 03/31/2005 17:15:12 MST . O X ? ) The time required to obtain this average.``.0 for 30 or more measurements) ’ It is known that the strength and relative positions of successive meter. by causing dropped counts or pulses.PERIOD JITTER AND ITS EFFECT O N CALIBRATION (This Appendix is not a part of ASME MFC-6M-1998 and is included for information purposes only.`. N. a determination of the period would invariably lead to an average period ( 7 ) and a standard deviation (u) for that average. The following discussion is confined to the physical principle of vortex shedding.. If a sufficiently large number of period measurements is obtained.) n = the number of period measurements Ali methods of on-line measurement of fluid flow are affected more or less by the fluctuations associated with turbulent flow (often referred to as “flow noise”). The random uncertainty of the average period to 95% confidence would then be given by: 6 = = ith period measurement 6 = error in the average period in percent 100xtxo2 N=( T.’ it is generally known that small.````.`. These changes are associated with the nature of the turbulent flow phenomena and can cause frequency jitter and amplitude variations in the output of a detector.`.`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale. Regarding period jitter.” T. In the case of vortex measurement.... can affect the performance of a meter.`.STD-ASIE I F C .. the number of pulses that must be counted in order to determine a flowrate to within a pre-assigned uncertainty of IC 816..`. 0 0.```.24 and if the standard deviation for period measurements is given by: looxu -- 0604065 O96 .-`-`..27.A S M E MFC-bM-ENGL L99B m 0757670 K = mean K factor qv = volumetric flowrate a = averaging time r Velocity.25% It can therefore be seen that if St does not vary with flowrate (not necessarily a good assumption).0 1. if a meter has a Strouhal number of 0. the averaging time of the meter associated with only the period uncertainty of vortex shedding is inversely proportional to the fluid velocity or the volumetric flowrate.`..6 3.`.24 x U d D = 6 0 0 ~ -= 1 6 0 ~ U U The calculated averaging times for 25 mm and 145 mm meters having these characteristics are given in Table A-1. becomes: IO Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS D=145mm Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.. a.0 7.5 13. 03/31/2005 17:15:12 MST --`.``..then the time.`..5) x d 1.`. m/r D=25mm 0. which. The manufacturer should be consulted for details regarding the effect of this phenomena on hisher meter.. NEEDED FOR A FLOWRATE UNCERTAINTY OF 0. the times in the above table must be multiplied by 4.31 3.S T D .`.`.5% a = and if dlD = 0. Note that.51 0. a.1 6.`--- Meter Size Flow I - m TABLE A-1 TIME. required to obtain an average flowrate with an uncertainty of 0.````. For example.35 63.. upon substituting the above mentioned values and assuming N is large.051 76.25% is given by: - 12 0. the averaging time for low velocity flows in large conduits is large enough to require a considerable integration time to obtain high accuracy after upsets in the flowrate.30 GENERAL NOTE: a = sec [&x 1.`. Thus. if 100 x y = 3%.`..3 0. fax.`--- Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Instituto Mexicano Del Petroleo/3139900100 Not for Resale.`.I7 17 973-882-5 155 Infocentral @asme. we make every effort to answer your questions and expedite your orders.. All technical inquiries must be submitted in writing to the staff secretary. Additional procedures for inquiries may be listed within. phone. New Jersey 07007-2900 * Call To11 Free US & Canada: 800-THE-ASME (800-843-2763) Mexico: 95-800-THE-ASME (95-800-843-2763) Universal: 973-882. Mail ASME 22 Law Drive.````..`. Box 2900 Fairfield.`. or E-mail us and an Information Central representative will handle your request..```...`. 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At ASME’s Infomation Central. --`.org Information Central staff are not permitted to answer inquiries about the technical content of this code or standard.`..`.`. 03/31/2005 17:15:12 MST .``.`.