godok.id

2. PRINCIPLE. OF OPERATIONThe principle of operation of the clamp-on transit-time flowmeter Is described in conjunction withFigure 1. Shown Is the high precision system that uses the patented Wide Beam clamp-ontransducer.AXIALBEAMINJECTIONFLOW -DOWNSTREAMTRANSDUCERFigure 1: Wide Beam Transit-Time PrincipleAs shown, the Wide Beam transducer excites a natural acoustic waveguide mode of the pipe soas to induce a sonic wave which travels axially down the pipe wall. As it travels it 'rains' sonicenergy through th liquid in the form of a wide beam. This beam arrives at the far wall and travelsdown toward the receive transducer, where It Is collected. Note that Figure 1 shows what is called'Direct' transducer mounting. An alternate 'Reflect' mounting is available, in which bothtransducers are mounted on the same side of the pipe.The advantage of the Wide Beam is that the angle of refraction of the beam is a function of theliquid sonic propagation velocity, hich varies from about 600 meters per second for very lightcompressed gasses, to about 1500 meter per second for heavy crude oils. The wide beamassures that no matter what liquid Is In the pipe, and what its refraction angle is, the beam willstill cover the receive transducer and permit continuous operation of the system. In fact, thismeter can operate on sequential batches of compressed gas, followed by oil, without requiringany human intervention or readjustment.Sonic energy Is injected alternately in the 'downstream' and 'upstream' directions. When sentupstream, the travel time required to reach the opposite transducer is longer than when sentdownstream, proportional to the actual flow velocity. Thus the meter's ability to measure the flowrate is based on measurement of this time difference.Note that the meter also measures the actual time required for the beam to travel across thepipe, and thus It can measure the actual sonic propagation velocity of the liquid. The sonicvelocity of the liquid Is a function of Its density, and therefore the transit-time meter can identifythen correlate to the API number of the liquid In the pipe at all times, with a resolution of 1 partin over 200,000. Since the meter takes approximately 1000 measurements per second, it isalways aware of what liquid Is in the pipe. It can therefore detect the interface between differentbatches of liquid, and can detect the presence of water in oil.Page3

Since the presence of free gas 'scatters' the sonic beam to some degree, It affects the amplitudeof the received sonic signal. This Is very useful in that It permits the detection of 'Aeration· th term applied to the presence of free gas. whether Included in the source product, or derived fromdepressurization or cavitation. A numeric value Is assigned to the degree of aeration, which Isreported as output data.If a pipe empties. the sonic beam is completely interrupted. This loss of signal is monitored bythe meter which issues an Empty Alarm if such a condition occurs.3. APPLICATIONREQUIREMENTS3.1 PIPE & LIQUID SONIC PROPERTIESThe Clamp-on Transit-time Ultrasonic meter Is among the most widely applicable of all flowmetertypes. This is because the only thing that Is required for operation is that the pipe wall be sonlcatlyconductive, and that the liquid also be sonically conductive. All common pipe materials aresonically conductive. as are all liquids.3.2 STRAIGHT RUN REQUIREMENTSMost ffowmeters require Installation with at least 1O diameters upstream, and 5 diametersdownstream. straight run. In addition, some flowmeters require upstream straighteners to defeatswirl effects. While substantial straight run, and avoidance of swirl, are desirable for an flowmeter, In the pipeline industry accessible pipe is frequently of limited length, and ofter severely populated with bends and elbows.·Fortunately, where long straight runs are simply not available, mounting directly adjacent tobends and elbows is permitted for clamp-on transit-time flowmeter transducers. This Is becausethe process of optimization reveals any calibration effects due to these conditions, and permitsthem to be counteracted at all flow rates, and tor all liquids. even If of highly variable viscosity.This process also reduces the need for frequent proving, since the behavior ot a given type ofliquid is 'remembered' and the correct calibration is automatically Installed. In addition, the factthat the transducers are clamp-on permits the Installer to try several different locations, andsimply select the one which shows the minimum evidence of flow profile dlstonion.Where flow profile Is severely aberrated due to nearby bends and elbows. or Intrusive elementssuch as pumps and valves, It Is recommended that a multi-path transducer Installation beemployed to average out the profile distortions. They are available in dual. trlple or four pathmodels. In general, dual path systems are sufficient for all but the most severely distorted profileconditions. In addition, the use of a transducer mount configuration where the transducersreceive a reflection of the transmit signal (Reflect mode) completely eliminates any error due tonon-axial flow. Swirl, other than Its effect in flattening the flow profile, has absolutely no effecton clamp-on flowmeter calibration.3.3 TRANSDUCER MOUNTING LOCATION ENVIRONMENTClamp-on transit-time transducers are available for any conceivable environment. They can beInstalled above or below ground, and can be installed under water. In addition, transducers ofthis type are capable of operation at very high and low temperatures, such as at 450"F in nuclearpower plants, and as installed on the Trans-Alaska Plpellne.3.4 VIBRATIONClamp-on transit-time transducers are completely immune to vibration, other than the need touse the appropriate mounting accessory.Page4

4. FUNCTIONS & OUTPUT DATA PROVlDEDOnce per minute, clamp-on transit-time site stations provide the master station with the followingdata: Flow Rate (Average over the last minute for each path) Flow Total Liquid Temperature Ambient Temperature Liquid Sonic Properties:- Sonic Propagation Velocity, Vs- Sonic Signal Strength, Vale- Liquid Aeration, Vaer Timed-Stamped Maximum Rate of Change of Vs Site Station Diagnostic Data:- Empty Pipe Alarm- Flow Direction- Operation Fault- Aeration AlarmIn addition to providing data to the leak detector master station, each site station Is capable ofproviding local site control, flow rate alarms and empty pipe alarms, etc. The same data as isprovided to the master station can be fed to the pipeline SCADA system in parallel. Output datais available in every standard data format, such as 4 to 20 mA, O to 1O Volts, and RS-232.5. PERFORMANCE PARAMETERSIt is surprising to some that the performance parameters of the clamp-on transit-time meter aresuperior to those of the conventional Intrusive flowmeters, since there is an intuitive 'feeling' thatsomething that is in actual contact with the liquid 'must' be superior to a meter whose sensingis non-intrusive. However, when one considers that the intrusive meter calibration suffers fromwear, coulomb and viscous friction, and residual flow profile distortion, it becomes fairly obviousthat the intrusive meter derives Its reputation for accuracy primarily from periodic proving, andprover repeatabillty.When proving is done at least once for a batch of uniform produ t. and the flow rates and otherconditions remain stable, the accuracy obtained for the total batch volume can be excellent.However, on many occasions, batches of product are not uniform, .and flow rates and liquidtemperatures can vary significantly. Under these conditions, unless proving is done frequently,the calibration factor obtained for Infrequent proving will not provide accurate meter factors.In addition, it is essential to recognize that periodic proving is quite adequate for custody transferpurposes. However, periodic proving of leak detection meters is not adequate. This is becausethe accuracy of a batch is determined on the scale of many hours or even days. The accuracyof a leak detection system must be maintained for periods as short as 1 minute, to assuredetection of a leak In the fastest possible time, and to avoid false alarms which defeat operatorconfidence in the system. Periodic proving, no matter how precise at the time it is performed,cannot protect a conventional intrusive meter leak detection system from inaccuracy at the 1and 5 minute Interval level, since batches of product are frequently non-uniform, and physicalconstraints prevent such frequent cycling.On the other hand, the clamp-on transit-time leak detection system identifies the product onceper minute. Even a small batch non-uniformity cannot escape detection. And through the processof optimization, subsequently described in detail, the correct meter calibration factor is alwaysprovided.Pages

.··The performance parameters and functions provided by the clamp-on transit-time site stationInclude:·Pt:RFO .1t:NCE ptull.ll - TER5Flow RanaeFrom o to 60 ft/sec flow velocltv (bl-directional)Flow Sensitivity0.001 ft/sec at anv flow rate lncludina 2eroLiquid Br. AmbientTemperature Accuracv0.1 FCalibration Reoeatabilltv0.02 to 0.1%Revnold's NumberFrom 1to109Flow Change Bandwidth10 HzFlow Slew Rateeo ft/sec2Temperature Rating- Flow Computer from -40 to 1ss F- Transducers from - eo to 450 FSafety RatingsClass 1, Div 1 & Div 2· NEMA 4X & NEMA 7Site Station Power Reaulrement15 wattsInterface Detection Resolution1 part in 200,000 tIFUNCTIONSBuilt-in Oatalogger with Site Identification and Time Stamp9600 Baud, RS-232 1/0 Serial Data CommunicatloriBuilt-in Diagnostics alerts user to liquid/system conditionsBuilt-in Pig detection6. INSTAUATIONLOGISTICSInstallation of a clamp-on transit-time flowmeter is quite simple, taking from 1 /2 to t 1/2 hours.It generally follows the procedure below:a)Installation site selection based on site survey, with a portable clamp-on transit-time .flowmeter to check actual flow characteristics of several candidate transducer locations, or from site drawings, a particular location is selected. The preferences willbe for as much straight run as convenient, in combination with avoidance of locationImmediately downstream of cavitation sources.b)Identify pipe outer diameter. material and wall thicknessc)d)Install mounting tracks plus flow and temperature transducers.e)Start up flow computer, and then set Initial adjustmentst)Check basic flow operation of installed meter.g)Print out Site Setup and System Diagnostic parameters for future referenceMount flow computer and connect cables to transducers- Page6

. . . '7. CLAMP-ON TRANSIT-TIME LEAK DETECTION SYSTEM DESCRIPTIONSince substantial literature describing the clamp-on transit-time leak detection system In greatdetail is available, this paper will, in the Interests of space, limit itself to a broad description ofthe system. Additional information can be obtained by writing or calling the author:Master StationCoMO!e'Deta StorageleakAnnunciatorColor PrinterDual PathFlow-Detectian.,,S iteStation1r:::--lt---- Modem ---tE::::::::::JData Link AmbientTemperatureClamp-OnLiquidTemperatureSensor- SiteStation\.-2SenaorClamp-OnAowTransducets n Figure 2: Transit-Time Leak Detection System SchematicReferring to Figure 2, It Is seen that the clamp.on transiMlme leak detection system consists ofa number of site stations, Installed at various distances from each other along the pipeline. Theseparation between site stations Is chosen dependent on the risk factor of the interveningsegment. The maximum segment length recommended is about 30 miles. although test casesinvolving segments over 100 miles have been successful.As shown, each site station Includes a single, dual or triple path clamp-on transit-time flowcomputer, plus clamp-on temperature sensors to measure both the liquid and ambienttemperature, as required by the type of system specified. Also Included at each site station iscommunication equipment, for either phone line, radio or satellite communication, as required.Page7

. The master station Is also equipped with a communication port. the master station Is the contro.J.center of the system, and processes all Incoming data to provide both alarms and pipelln.operations data, dependent on which type of system has been specified. The master station alsoarchives all incoming data Into dally data flies, which can subsequently be analyzed to permitsystem optimization, and to provide a playback capability in order to show due diligence, whennecessary.Master stations are available to handle any and all pipeline configurations, so that expensive andtime consuming custom leak detection system design is avoided. Instead, provision is made forthe actual physical configuration of any pipeline to be described in a generic topology file, whichIs prepared for installation Into the master station. Thus the master station interprets all sitestation data by referring to the topology file, which tells the standard master station operatingsystem how to handle this data to provide for accurate and reliable leak detection performance.The master station polls all site stations once per minute simultaneously. Some models canhandle as many as 64 site stations, which can be on any number of Independent individualpipeline systems as desired, up to the capacity of the master station. Upon receipt of the data,It proceeds to compute the temperature and line pack corrected volume balance for eachsegment of each pipeline registered. It also computes a number of addltlonal factors which areuseful in determining the validity of a leak alarm, such as the current application and equipmentoperating conditions. It also computes data useful for management of the pipeline, such a ;.Interface detection, batch tracking, liquid type Identification, llquid quality determination, p i detection and many other Important factors.At the completion of this computation, which takes less than one minute, The master stationpublishes all computed data. If there Is a breach of one of four leak detection thresholds, for 1,5, 15 and 60 minute periods, the leak alarm Is activated, generating both audible and visiblealarms. Up to this point, the system need not be actively monitored, unless Its many operationsmanagement screens, such as those for interface detection or batch tracking, are utilized forpipeline management.As detailed In the additional available literature, a complete description of the many data screensare provided. Suffice It to say, master stations can produce a substantial amount of very usefuldata, all of It presented In both graphics and numeric data screen formats. These are displayedby simply.depressing an appropriate master station 'hot key'. The screens are organized in asequence so that the system operator can quickly determine which segment of the pipelinegenerated the leak alarm. Many of these screens are of multi-graph type, which permits theinspection of as many as four different data Items simultaneously. The · operator, or userdesignated staff, can then easily associate various cause and effect relationships, so as toquickly make a decision as to the validity of the leak alarm.In addition, communication links to the leak detection system supplier's headquarters per4experienced system engineers to assist In diagnosis of leak conditions.In order to avoid false alarms, the system should Include an automatic application conditionmonitoring function. If deteriorated liquid or other operating conditions are responslbl e for a leakalarm, there Is an automatic readjustment of the alarm threshold to avoid the false alarm.However, such a condition wlll also trigger the leak warning so as to alert the operating staff ofthe potential of an as yet undeclared leak alarm. In addition, the process of optimization furtherensures against the generation of false alarms, while also enabling the settlng of the minimumpossible alarm threshold.7.1 LINE PACK & THERMAL EXPANSION/CONTRACTION DETECTIONThe clamp-on transit-time flowmeter automatically detects both line pack and, for systems Inwhich temperature gradients are expected, It also determines the effect of liquid and pipelineexpansion or contraction, so as to preclude either false alarms, or failure to detect a leak.Page a

a) Line Pack DetectionThe clamp-on transit-time leak detector has a unique advantage In the detection of line pack, orunpack. This Is because compression of the liquid, as In line pack, also Increases the liquiddensity. This increase In density Is sensed as a sudden increase in Vs, the liquid's sonicpropagation velocity. Thus, by correlating the increase In flow rate with the Increase In Vs, It iseasy to confirm that the current segment volume Imbalance is due to line pack, and not a leak,thus preventing the declaration of a false leak alarm.However, during the process of optimization, a determination Is made as to the amount of liquidwhich is normally packed in each pipeline segment under.various flow conditions. Using thisdata, the leak detection system Is able to sense If the actual liquid unbalance, during line packevents, Is within the historical limit. If It exceeds this limit, as if the pipeline leaked during the linepack event, the system will Immediately declare a leak alarm.b) Correction for Thermal Expansion or ContractionThe clamp-on transit-time leak detector senses both the liquid and ambient temperature at eachsite station. It uses this data, In combination with the thermal model of the pipeline, containedin the master station topology file, to compute the temperature of the liquid and pipe wall at 100points between site stations. This is done for all pipeline segments once per minute. Thesetemperatures are used to compute the Incremental expansion or contraction of both the liquidand the pipeline for each segment registered in the master station. This volumetric data is eitheradded to, or subtracted from, the measured segment volume Imbalance, so as to prevent eithera false alarm, or masking a true alarm condition.Assuring that the thermal model of the pipeline Is working property is relatively simple. One ofthe points whose temperature is computed is at the next site station, where actual measurementof the liquid temperature Is being made. If the parameters of the thermal model were not correct,the computed and measured temperatures would not coincide. If they do not coincide at first,the process of optimization determines the correct thermal model operating parameters toachieve coincidence. Since both the computed and measured temperatures are presented onone screen, the operator can easily confirm that the thermal model is operating properly.7.2 INTERFACE DETECTIONInterface detection Is frequently performed by sampling the product In the pipeline periodically,and physically measuring Its density. Alternatively, expensive and maintenance pronedensitometers are used. But, note that Vs, the sonic propagation velocity of the liquid, Is afunction of liquid density. The clamp-on transit-time flowmeter can sense the change in Vs , andthereby density, with considerably more sensitivity than conventional densitometers. ·The clamp-on transit-time leak detection system uses this Vs data, in combination with themeasured liquid temperature, to compute the 'sonic signature' of each liquid. This uniquelyIdentifies the liquid, enabling computation of Its current density, and its density at 60 F.This leads directly to the API number determination. Both the sonic signature and API numberof the batch are plotted as a function of time. These screens are available for real time interfacedetection, and the data Is also made available as a local output from each site station.7.3 BATCH TRACKINGSince the clamp-on transit-time leak detection system can Identify the liquid in the pipe at alltimes, and has full knowledge of the time history of flow rates, It is a relatively straightforwardmatter to compute the location of all batch Interfaces within each pipeline segment. Marking theInterfaces between batches also permits the system to compute the actual standard volume of'each batch. Thus data screens are available to show the actual volume of each batch, where theInterfaces are at any given time, and to predict the arrival time of all batches at their next targetsite station.Page9

.7.4 CUSTODY TRANSFERClearly, the entire batch tracking function available from clamp-on transit-time leak detecttortlsystems is based on the ablllty of this ultrasonic flowmeter to Identify each batch of liquid, Itsdensity and API number. It Is already well established that clamp-on transit-time meters can bevolumetrically proved, using the conventional API proving method. The only q uestion whichremains to determine Its candidacy for custody transfer service Is to establish Its 'long and shortterm calibration stability. Tests of this

PERFORMANCE OF CLAMP-ON ULTRASONIC FLOWMETER PIPELINE LEAK DETECTION SYSTEMS 1. INTRODUCTION J, BAUMOEL, PRESIDENT CoNTROLOTRON CORPORATION HAUPPAUGE, LONG ISLAND, NEW YORK 11788 PHONE: 51 231-3600 FAX: 51 231-3334 Recent enhanced awareness of th